详解Android布局加载流程源码

206 阅读 0 评论 136 点赞

我是靠谱客的博主清爽中心，这篇文章主要介绍详解Android布局加载流程源码，现在分享给大家，希望可以做个参考。

一.首先看布局层次看这么几张图

我们会发现DecorView里面包裹的内容可能会随着不同的情况而变化，但是在Decor之前的层次关系都是固定的。即Activity包裹PhoneWindow，PhoneWindow包裹DecorView。接下来我们首先看一下三者分别是如何创建的。

二.Activity是如何创建的

首先看到入口类ActivityThread的performLaunchActivity方法:

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {      
		...
        ContextImpl appContext = createBaseContextForActivity(r);
        Activity activity = null;
        try {
            java.lang.ClassLoader cl = appContext.getClassLoader();
            activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            StrictMode.incrementExpectedActivityCount(activity.getClass());
            r.intent.setExtrasClassLoader(cl);
            r.intent.prepareToEnterProcess();
            if (r.state != null) {
                r.state.setClassLoader(cl);
            }
        } catch (Exception e) {
            ...
        }

有句特别关键的代码，即

复制代码

1
activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);

所以activity是Instrumentation类的newActivity方法创建的，追踪过去，源码如下

复制代码

1
2
3
4
5
6
7
8
public Activity newActivity(ClassLoader cl, String className,
            Intent intent)
            throws InstantiationException, IllegalAccessException,
            ClassNotFoundException {
        String pkg = intent != null && intent.getComponent() != null
                ? intent.getComponent().getPackageName() : null;
        return getFactory(pkg).instantiateActivity(cl, className, intent);
    }

追踪源码，可知getFactory方法返回一个AppComponentFactory对象，然后调用AppComponentFactory的instantiateActivity方法，继续追踪

复制代码

1
2
3
4
5
public @NonNull Activity instantiateActivity(@NonNull ClassLoader cl, @NonNull String className,
            @Nullable Intent intent)
            throws InstantiationException, IllegalAccessException, ClassNotFoundException {
        return (Activity) cl.loadClass(className).newInstance();
    }

到这里就结束了，我们可以发现Activity是通过反射创建的。

三.PhoneWindow的创建

我们还是回到ActivityThread的performLaunchActivity方法，在刚刚展示的那一段的下面有如下部分代码

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Window window = null;
        if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
            window = r.mPendingRemoveWindow;
            r.mPendingRemoveWindow = null;
            r.mPendingRemoveWindowManager = null;
        }

        // Activity resources must be initialized with the same loaders as the
        // application context.
        appContext.getResources().addLoaders(
                app.getResources().getLoaders().toArray(new ResourcesLoader[0]));

        appContext.setOuterContext(activity);
        activity.attach(appContext, this, getInstrumentation(), r.token,
                r.ident, app, r.intent, r.activityInfo, title, r.parent,
                r.embeddedID, r.lastNonConfigurationInstances, config,
                r.referrer, r.voiceInteractor, window, r.configCallback,
                r.assistToken);

在activity.attach这个方法中，传入了一个Window对象，追踪这个attach方法，里面有一句关键代码

复制代码

1
mWindow = new PhoneWindow(this, window, activityConfigCallback);

此时就创建了PhoneWindow。所以我们可以知道，在Activity创建完之后，会为当前的Activity创建一个PhoneWindow对象。

四.DecorView的创建

DecorView的创建就不是performLaunchActivity方法里面了，这次我们从Activity的setContentView的源码开始分析。下面的Activity的setContentView方法的内容。

复制代码

1
2
3
4
public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }

我们发现，Activity的setContentView实际是调用了PhoneWindow的setContentView方法，跟踪源码。我们会首先进入Window抽象类，然后我们找其子类PhoneWindow，在里面找到setContentView方法

复制代码

1
2
3
4
5
6
7
public void setContentView(int layoutResID) {
        if (mContentParent == null) {
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }
		...

当mContentParent为null时，会调用installDecor方法，追踪进入

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1);
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            mDecor.setWindow(this);
        }
        ...

它调用了generateDecor方法，追踪进入

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
protected DecorView generateDecor(int featureId) {
        // System process doesn't have application context and in that case we need to directly use
        // the context we have. Otherwise we want the application context, so we don't cling to the
        // activity.
        Context context;
        if (mUseDecorContext) {
            Context applicationContext = getContext().getApplicationContext();
            if (applicationContext == null) {
                context = getContext();
            } else {
                context = new DecorContext(applicationContext, this);
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context, featureId, this, getAttributes());
    }

会发现generateDecor方法会创建一个DecorView对象，并且作为返回值返回。再追踪DecorView

复制代码

1
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks

会发现DecorView其实是一个FrameLayout 。到这就介绍完DecorView是如何创建的了

五.布局加载流程

我们回到PhoneWindow的installDecor方法，再刚刚看的部分的下面，有（2692行）

复制代码

1
if (mContentParent == null) {mContentParent = generateLayout(mDecor);

追踪进入

复制代码

protected ViewGroup generateLayout(DecorView decor) {
        // Apply data from current theme.

TypedArray a = getWindowStyle();

if (false) {
            System.out.println("From style:");
            String s = "Attrs:";
            for (int i = 0; i < R.styleable.Window.length; i++) {
                s = s + " " + Integer.toHexString(R.styleable.Window[i]) + "="
                        + a.getString(i);
            }
            System.out.println(s);
        }

mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);
        int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
                & (~getForcedWindowFlags());
        if (mIsFloating) {
            setLayout(WRAP_CONTENT, WRAP_CONTENT);
            setFlags(0, flagsToUpdate);
        } else {
            setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
            getAttributes().setFitInsetsSides(0);
            getAttributes().setFitInsetsTypes(0);
        }

if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
            requestFeature(FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
            // Don't allow an action bar if there is no title.
            requestFeature(FEATURE_ACTION_BAR);
        }

if (a.getBoolean(R.styleable.Window_windowActionBarOverlay, false)) {
            requestFeature(FEATURE_ACTION_BAR_OVERLAY);
        }

if (a.getBoolean(R.styleable.Window_windowActionModeOverlay, false)) {
            requestFeature(FEATURE_ACTION_MODE_OVERLAY);
        }

if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
            setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
        }

if (a.getBoolean(R.styleable.Window_windowTranslucentStatus,
                false)) {
            setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS
                    & (~getForcedWindowFlags()));
        }

if (a.getBoolean(R.styleable.Window_windowTranslucentNavigation,
                false)) {
            setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION
                    & (~getForcedWindowFlags()));
        }

if (a.getBoolean(R.styleable.Window_windowShowWallpaper, false)) {
            setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
        }

if (a.getBoolean(R.styleable.Window_windowEnableSplitTouch,
                getContext().getApplicationInfo().targetSdkVersion
                        >= android.os.Build.VERSION_CODES.HONEYCOMB)) {
            setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));
        }

a.getValue(R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);
        a.getValue(R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);
        if (DEBUG) Log.d(TAG, "Min width minor: " + mMinWidthMinor.coerceToString()
                + ", major: " + mMinWidthMajor.coerceToString());
        if (a.hasValue(R.styleable.Window_windowFixedWidthMajor)) {
            if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedWidthMajor,
                    mFixedWidthMajor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedWidthMinor)) {
            if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedWidthMinor,
                    mFixedWidthMinor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedHeightMajor)) {
            if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedHeightMajor,
                    mFixedHeightMajor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedHeightMinor)) {
            if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedHeightMinor,
                    mFixedHeightMinor);
        }
        if (a.getBoolean(R.styleable.Window_windowContentTransitions, false)) {
            requestFeature(FEATURE_CONTENT_TRANSITIONS);
        }
        if (a.getBoolean(R.styleable.Window_windowActivityTransitions, false)) {
            requestFeature(FEATURE_ACTIVITY_TRANSITIONS);
        }

mIsTranslucent = a.getBoolean(R.styleable.Window_windowIsTranslucent, false);

final Context context = getContext();
        final int targetSdk = context.getApplicationInfo().targetSdkVersion;
        final boolean targetPreL = targetSdk < android.os.Build.VERSION_CODES.LOLLIPOP;
        final boolean targetPreQ = targetSdk < Build.VERSION_CODES.Q;

if (!mForcedStatusBarColor) {
            mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
        }
        if (!mForcedNavigationBarColor) {
            mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
            mNavigationBarDividerColor = a.getColor(R.styleable.Window_navigationBarDividerColor,
                    0x00000000);
        }
        if (!targetPreQ) {
            mEnsureStatusBarContrastWhenTransparent = a.getBoolean(
                    R.styleable.Window_enforceStatusBarContrast, false);
            mEnsureNavigationBarContrastWhenTransparent = a.getBoolean(
                    R.styleable.Window_enforceNavigationBarContrast, true);
        }

WindowManager.LayoutParams params = getAttributes();

// Non-floating windows on high end devices must put up decor beneath the system bars and
        // therefore must know about visibility changes of those.
        if (!mIsFloating) {
            if (!targetPreL && a.getBoolean(
                    R.styleable.Window_windowDrawsSystemBarBackgrounds,
                    false)) {
                setFlags(FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS,
                        FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS & ~getForcedWindowFlags());
            }
            if (mDecor.mForceWindowDrawsBarBackgrounds) {
                params.privateFlags |= PRIVATE_FLAG_FORCE_DRAW_BAR_BACKGROUNDS;
            }
        }
        if (a.getBoolean(R.styleable.Window_windowLightStatusBar, false)) {
            decor.setSystemUiVisibility(
                    decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);
        }
        if (a.getBoolean(R.styleable.Window_windowLightNavigationBar, false)) {
            decor.setSystemUiVisibility(
                    decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR);
        }
        if (a.hasValue(R.styleable.Window_windowLayoutInDisplayCutoutMode)) {
            int mode = a.getInt(R.styleable.Window_windowLayoutInDisplayCutoutMode, -1);
            if (mode < LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT
                    || mode > LAYOUT_IN_DISPLAY_CUTOUT_MODE_ALWAYS) {
                throw new UnsupportedOperationException("Unknown windowLayoutInDisplayCutoutMode: "
                        + a.getString(R.styleable.Window_windowLayoutInDisplayCutoutMode));
            }
            params.layoutInDisplayCutoutMode = mode;
        }

if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
                >= android.os.Build.VERSION_CODES.HONEYCOMB) {
            if (a.getBoolean(
                    R.styleable.Window_windowCloseOnTouchOutside,
                    false)) {
                setCloseOnTouchOutsideIfNotSet(true);
            }
        }

if (!hasSoftInputMode()) {
            params.softInputMode = a.getInt(
                    R.styleable.Window_windowSoftInputMode,
                    params.softInputMode);
        }

if (a.getBoolean(R.styleable.Window_backgroundDimEnabled,
                mIsFloating)) {
            /* All dialogs should have the window dimmed */
            if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) {
                params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
            }
            if (!haveDimAmount()) {
                params.dimAmount = a.getFloat(
                        android.R.styleable.Window_backgroundDimAmount, 0.5f);
            }
        }

if (params.windowAnimations == 0) {
            params.windowAnimations = a.getResourceId(
                    R.styleable.Window_windowAnimationStyle, 0);
        }

// The rest are only done if this window is not embedded; otherwise,
        // the values are inherited from our container.
        if (getContainer() == null) {
            if (mBackgroundDrawable == null) {

if (mFrameResource == 0) {
                    mFrameResource = a.getResourceId(R.styleable.Window_windowFrame, 0);
                }

if (a.hasValue(R.styleable.Window_windowBackground)) {
                    mBackgroundDrawable = a.getDrawable(R.styleable.Window_windowBackground);
                }
            }
            if (a.hasValue(R.styleable.Window_windowBackgroundFallback)) {
                mBackgroundFallbackDrawable =
                        a.getDrawable(R.styleable.Window_windowBackgroundFallback);
            }
            if (mLoadElevation) {
                mElevation = a.getDimension(R.styleable.Window_windowElevation, 0);
            }
            mClipToOutline = a.getBoolean(R.styleable.Window_windowClipToOutline, false);
            mTextColor = a.getColor(R.styleable.Window_textColor, Color.TRANSPARENT);
        }

// Inflate the window decor.

int layoutResource;
        int features = getLocalFeatures();
        // System.out.println("Features: 0x" + Integer.toHexString(features));
        if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleIconsDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_title_icons;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
            // System.out.println("Title Icons!");
        } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
                && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
            // Special case for a window with only a progress bar (and title).
            // XXX Need to have a no-title version of embedded windows.
            layoutResource = R.layout.screen_progress;
            // System.out.println("Progress!");
        } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
            // Special case for a window with a custom title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogCustomTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_custom_title;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
        } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
            // If no other features and not embedded, only need a title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
                layoutResource = a.getResourceId(
                        R.styleable.Window_windowActionBarFullscreenDecorLayout,
                        R.layout.screen_action_bar);
            } else {
                layoutResource = R.layout.screen_title;
            }
            // System.out.println("Title!");
        } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
            layoutResource = R.layout.screen_simple_overlay_action_mode;
        } else {
            // Embedded, so no decoration is needed.
            layoutResource = R.layout.screen_simple;
            // System.out.println("Simple!");
        }

mDecor.startChanging();
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
            ProgressBar progress = getCircularProgressBar(false);
            if (progress != null) {
                progress.setIndeterminate(true);
            }
        }

// Remaining setup -- of background and title -- that only applies
        // to top-level windows.
        if (getContainer() == null) {
            mDecor.setWindowBackground(mBackgroundDrawable);

final Drawable frame;
            if (mFrameResource != 0) {
                frame = getContext().getDrawable(mFrameResource);
            } else {
                frame = null;
            }
            mDecor.setWindowFrame(frame);

mDecor.setElevation(mElevation);
            mDecor.setClipToOutline(mClipToOutline);

if (mTitle != null) {
                setTitle(mTitle);
            }

if (mTitleColor == 0) {
                mTitleColor = mTextColor;
            }
            setTitleColor(mTitleColor);
        }

mDecor.finishChanging();

return contentParent;
    }

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
protected ViewGroup generateLayout(DecorView decor) {
        // Apply data from current theme.

        TypedArray a = getWindowStyle();

        if (false) {
            System.out.println("From style:");
            String s = "Attrs:";
            for (int i = 0; i < R.styleable.Window.length; i++) {
                s = s + " " + Integer.toHexString(R.styleable.Window[i]) + "="
                        + a.getString(i);
            }
            System.out.println(s);
        }

        mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);
        int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
                & (~getForcedWindowFlags());
        if (mIsFloating) {
            setLayout(WRAP_CONTENT, WRAP_CONTENT);
            setFlags(0, flagsToUpdate);
        } else {
            setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
            getAttributes().setFitInsetsSides(0);
            getAttributes().setFitInsetsTypes(0);
        }

        if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
            requestFeature(FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
            // Don't allow an action bar if there is no title.
            requestFeature(FEATURE_ACTION_BAR);
        }

        if (a.getBoolean(R.styleable.Window_windowActionBarOverlay, false)) {
            requestFeature(FEATURE_ACTION_BAR_OVERLAY);
        }

        if (a.getBoolean(R.styleable.Window_windowActionModeOverlay, false)) {
            requestFeature(FEATURE_ACTION_MODE_OVERLAY);
        }

        if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
            setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowTranslucentStatus,
                false)) {
            setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS
                    & (~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowTranslucentNavigation,
                false)) {
            setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION
                    & (~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowShowWallpaper, false)) {
            setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowEnableSplitTouch,
                getContext().getApplicationInfo().targetSdkVersion
                        >= android.os.Build.VERSION_CODES.HONEYCOMB)) {
            setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));
        }

        a.getValue(R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);
        a.getValue(R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);
        if (DEBUG) Log.d(TAG, "Min width minor: " + mMinWidthMinor.coerceToString()
                + ", major: " + mMinWidthMajor.coerceToString());
        if (a.hasValue(R.styleable.Window_windowFixedWidthMajor)) {
            if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedWidthMajor,
                    mFixedWidthMajor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedWidthMinor)) {
            if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedWidthMinor,
                    mFixedWidthMinor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedHeightMajor)) {
            if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedHeightMajor,
                    mFixedHeightMajor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedHeightMinor)) {
            if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedHeightMinor,
                    mFixedHeightMinor);
        }
        if (a.getBoolean(R.styleable.Window_windowContentTransitions, false)) {
            requestFeature(FEATURE_CONTENT_TRANSITIONS);
        }
        if (a.getBoolean(R.styleable.Window_windowActivityTransitions, false)) {
            requestFeature(FEATURE_ACTIVITY_TRANSITIONS);
        }

        mIsTranslucent = a.getBoolean(R.styleable.Window_windowIsTranslucent, false);

        final Context context = getContext();
        final int targetSdk = context.getApplicationInfo().targetSdkVersion;
        final boolean targetPreL = targetSdk < android.os.Build.VERSION_CODES.LOLLIPOP;
        final boolean targetPreQ = targetSdk < Build.VERSION_CODES.Q;

        if (!mForcedStatusBarColor) {
            mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
        }
        if (!mForcedNavigationBarColor) {
            mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
            mNavigationBarDividerColor = a.getColor(R.styleable.Window_navigationBarDividerColor,
                    0x00000000);
        }
        if (!targetPreQ) {
            mEnsureStatusBarContrastWhenTransparent = a.getBoolean(
                    R.styleable.Window_enforceStatusBarContrast, false);
            mEnsureNavigationBarContrastWhenTransparent = a.getBoolean(
                    R.styleable.Window_enforceNavigationBarContrast, true);
        }

        WindowManager.LayoutParams params = getAttributes();

        // Non-floating windows on high end devices must put up decor beneath the system bars and
        // therefore must know about visibility changes of those.
        if (!mIsFloating) {
            if (!targetPreL && a.getBoolean(
                    R.styleable.Window_windowDrawsSystemBarBackgrounds,
                    false)) {
                setFlags(FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS,
                        FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS & ~getForcedWindowFlags());
            }
            if (mDecor.mForceWindowDrawsBarBackgrounds) {
                params.privateFlags |= PRIVATE_FLAG_FORCE_DRAW_BAR_BACKGROUNDS;
            }
        }
        if (a.getBoolean(R.styleable.Window_windowLightStatusBar, false)) {
            decor.setSystemUiVisibility(
                    decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);
        }
        if (a.getBoolean(R.styleable.Window_windowLightNavigationBar, false)) {
            decor.setSystemUiVisibility(
                    decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR);
        }
        if (a.hasValue(R.styleable.Window_windowLayoutInDisplayCutoutMode)) {
            int mode = a.getInt(R.styleable.Window_windowLayoutInDisplayCutoutMode, -1);
            if (mode < LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT
                    || mode > LAYOUT_IN_DISPLAY_CUTOUT_MODE_ALWAYS) {
                throw new UnsupportedOperationException("Unknown windowLayoutInDisplayCutoutMode: "
                        + a.getString(R.styleable.Window_windowLayoutInDisplayCutoutMode));
            }
            params.layoutInDisplayCutoutMode = mode;
        }

        if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
                >= android.os.Build.VERSION_CODES.HONEYCOMB) {
            if (a.getBoolean(
                    R.styleable.Window_windowCloseOnTouchOutside,
                    false)) {
                setCloseOnTouchOutsideIfNotSet(true);
            }
        }

        if (!hasSoftInputMode()) {
            params.softInputMode = a.getInt(
                    R.styleable.Window_windowSoftInputMode,
                    params.softInputMode);
        }

        if (a.getBoolean(R.styleable.Window_backgroundDimEnabled,
                mIsFloating)) {
            /* All dialogs should have the window dimmed */
            if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) {
                params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
            }
            if (!haveDimAmount()) {
                params.dimAmount = a.getFloat(
                        android.R.styleable.Window_backgroundDimAmount, 0.5f);
            }
        }

        if (params.windowAnimations == 0) {
            params.windowAnimations = a.getResourceId(
                    R.styleable.Window_windowAnimationStyle, 0);
        }

        // The rest are only done if this window is not embedded; otherwise,
        // the values are inherited from our container.
        if (getContainer() == null) {
            if (mBackgroundDrawable == null) {

                if (mFrameResource == 0) {
                    mFrameResource = a.getResourceId(R.styleable.Window_windowFrame, 0);
                }

                if (a.hasValue(R.styleable.Window_windowBackground)) {
                    mBackgroundDrawable = a.getDrawable(R.styleable.Window_windowBackground);
                }
            }
            if (a.hasValue(R.styleable.Window_windowBackgroundFallback)) {
                mBackgroundFallbackDrawable =
                        a.getDrawable(R.styleable.Window_windowBackgroundFallback);
            }
            if (mLoadElevation) {
                mElevation = a.getDimension(R.styleable.Window_windowElevation, 0);
            }
            mClipToOutline = a.getBoolean(R.styleable.Window_windowClipToOutline, false);
            mTextColor = a.getColor(R.styleable.Window_textColor, Color.TRANSPARENT);
        }

        // Inflate the window decor.

        int layoutResource;
        int features = getLocalFeatures();
        // System.out.println("Features: 0x" + Integer.toHexString(features));
        if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleIconsDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_title_icons;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
            // System.out.println("Title Icons!");
        } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
                && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
            // Special case for a window with only a progress bar (and title).
            // XXX Need to have a no-title version of embedded windows.
            layoutResource = R.layout.screen_progress;
            // System.out.println("Progress!");
        } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
            // Special case for a window with a custom title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogCustomTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_custom_title;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
        } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
            // If no other features and not embedded, only need a title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
                layoutResource = a.getResourceId(
                        R.styleable.Window_windowActionBarFullscreenDecorLayout,
                        R.layout.screen_action_bar);
            } else {
                layoutResource = R.layout.screen_title;
            }
            // System.out.println("Title!");
        } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
            layoutResource = R.layout.screen_simple_overlay_action_mode;
        } else {
            // Embedded, so no decoration is needed.
            layoutResource = R.layout.screen_simple;
            // System.out.println("Simple!");
        }

        mDecor.startChanging();
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

        if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
            ProgressBar progress = getCircularProgressBar(false);
            if (progress != null) {
                progress.setIndeterminate(true);
            }
        }

        // Remaining setup -- of background and title -- that only applies
        // to top-level windows.
        if (getContainer() == null) {
            mDecor.setWindowBackground(mBackgroundDrawable);

            final Drawable frame;
            if (mFrameResource != 0) {
                frame = getContext().getDrawable(mFrameResource);
            } else {
                frame = null;
            }
            mDecor.setWindowFrame(frame);

            mDecor.setElevation(mElevation);
            mDecor.setClipToOutline(mClipToOutline);

            if (mTitle != null) {
                setTitle(mTitle);
            }

            if (mTitleColor == 0) {
                mTitleColor = mTextColor;
            }
            setTitleColor(mTitleColor);
        }

        mDecor.finishChanging();

        return contentParent;
    }

分析源码和源码注释可以看出generateLayout方法的核心功能是完成DecorView的布局加载，而且根据不同的主题样式会加载不同的系统默认布局。那么比如有FrameLayout布局，它如何加载到DecorView中呢？
在generateLayout方法中，有这么一句

复制代码

1
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

追踪进入

复制代码

void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
        if (mBackdropFrameRenderer != null) {
            loadBackgroundDrawablesIfNeeded();
            mBackdropFrameRenderer.onResourcesLoaded(
                    this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
                    mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
                    getCurrentColor(mNavigationColorViewState));
        }

mDecorCaptionView = createDecorCaptionView(inflater);
        final View root = inflater.inflate(layoutResource, null);
        if (mDecorCaptionView != null) {
            if (mDecorCaptionView.getParent() == null) {
                addView(mDecorCaptionView,
                        new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
            }
            mDecorCaptionView.addView(root,
                    new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
        } else {

// Put it below the color views.
            addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
        }
        mContentRoot = (ViewGroup) root;
        initializeElevation();
    }

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
        if (mBackdropFrameRenderer != null) {
            loadBackgroundDrawablesIfNeeded();
            mBackdropFrameRenderer.onResourcesLoaded(
                    this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
                    mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
                    getCurrentColor(mNavigationColorViewState));
        }

        mDecorCaptionView = createDecorCaptionView(inflater);
        final View root = inflater.inflate(layoutResource, null);
        if (mDecorCaptionView != null) {
            if (mDecorCaptionView.getParent() == null) {
                addView(mDecorCaptionView,
                        new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
            }
            mDecorCaptionView.addView(root,
                    new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
        } else {

            // Put it below the color views.
            addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
        }
        mContentRoot = (ViewGroup) root;
        initializeElevation();
    }

关键在这里

复制代码

1
2
3
4
5
6
7
mDecorCaptionView = createDecorCaptionView(inflater);
final View root = inflater.inflate(layoutResource, null);
if (mDecorCaptionView != null) {
    ...
    mDecorCaptionView.addView(root,
            new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
}

可以看到layoutResource作为参数，通过inflate方法进行解析加载。然后作为参数，传入addView方法，将布局挂载到上面。至此完成了DecorView的默认布局加载。如果是我们自己编写的布局是如何加载呢？再回到generateLayout的

复制代码

1
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

，在此之后，有这么一句

复制代码

1
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);

在DecorView执行onResourcesLoaded方法加载完默认布局后，会查找Id为ID_ANDROID_CONTENT的控件(默认布局中的FrameLayout控件)并作为generateLayout方法的返回值，我们回到setContentView方法中，可观察到以下代码：

复制代码

1
mLayoutInflater.inflate(layoutResID, mContentParent);

所以，我们自己编写的布局是被加载到DecorView中Id为ID_ANDROID_CONTENT的控件上

六.总结

当Activity创建后会创建出一个PhoneWindow对象，当在Activity中调用setContentView时，实际上是调用了PhoneWindow的setContentView方法，此时PhoneWindow会创建根布局DecorView，并根据主题样式，为DecorView加载对应的默认系统布局，在默认的系统布局中包含了一个Id为ID_ANDROID_CONTENT的控件，而我们自己编写的布局就是加载到这个控件中的。

以上就是详解Android布局加载流程源码的详细内容，更多关于Android布局加载流程源码分析的资料请关注靠谱客其它相关文章！