一种无需留坑为页面动态添加View方案

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我是靠谱客的博主纯真飞机，最近开发中收集的这篇文章主要介绍一种无需留坑为页面动态添加View方案，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

在Activity或Fragment页面动态添加View，有其应用场景，比如配合运营在首页动态插入H5活动页（如下图手淘的雪花例示[1]）,在页面头部插入通知View等。本文结合ActivityLifecycleCallbacks[2]及DecorView使用，为类似需求提供一种解决方案。

方案概述

本文方案监听Activity生命周期，在拿到指定Activity后，获取PhoneWindow.mContentParent，并在mContentParent中addView。

监听Activity生命周期

在android API 14+ ,Application.registerActivityLifecycleCallbacks(ActivityLifecycleCallbacks callback)提供了一套回调方法，用于对Activity的生命周期事件进行集中处理。我们可用ActivityLifecycleCallbacks玩出很多花样，比如页面埋点，router预处理，限制Activity实例个数，swipeback等等。在本文它keep当前activity引用。

public interface ActivityLifecycleCallbacks {
    void onActivityCreated(Activity activity, Bundle savedInstanceState);
    void onActivityStarted(Activity activity);
    void onActivityResumed(Activity activity);
    void onActivityPaused(Activity activity);
    void onActivityStopped(Activity activity);
    void onActivitySaveInstanceState(Activity activity, Bundle outState);
    void onActivityDestroyed(Activity activity);
}

PhoneWindow.mContentParent获取

Android的页面组成[3]如下图（注:在sdk 14+或在19+AppCompat，mContentParent不包含Actionbar，既标题栏[4]），我们关心如何获取mContentParent。

在此简单例出mContentParent的相关代码

    /**
     *Activity.setContentView，此处的getWindow返回PhoneWindow,在
     *activity.attach方法中实例化
     **/
    public void setContentView(@LayoutRes int layoutResID) {
                    getWindow().setContentView(layoutResID);
                    initWindowDecorActionBar();
    }
    
    /**
     *PhoneWindow.setContentView
     **/    
    public void setContentView(int layoutResID) {
               ...
               if (mContentParent == null) {
                mContentParent = generateLayout(mDecor);
                }
                ...
     }
    
    /**
     * mContentParent 从DecorView中ID为ID_ANDROID_CONTENT中赋值；ID_ANDROID_CONTENT在PhoneWindow中是一个int常量
     * public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
     **/   
    protected ViewGroup generateLayout(DecorView decor) {
     ...
       ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
            if (contentParent == null) {
                throw new RuntimeException("Window couldn't find content container view");
            }
      ...
      return contentParent;
    }
  
/**
 *Activity.findViewById
 **/  
public View findViewById(@IdRes int id) {
        return getWindow().findViewById(id);
    }
/**
 *PhoneWindow.findViewById
**/
public View findViewById(@IdRes int id) {
        return getDecorView().findViewById(id);
    }

从上述代码我们可以发现，mContentParent可以通过activity.findViewById(android.R.id.content)获取。

方案实现

此方案两个关键：keep Activity实例和获取id为android.R.id.content的View。下面列出核心代码。

public class Background implements Application.ActivityLifecycleCallbacks {

    /**
     * 用于检测当前APP是否运行于前台
     */
    private int appCount = 0;

    private WeakReference<Activity> mActivity;


    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {

    }

    @Override
    public void onActivityStarted(Activity activity) {
        appCount++;
    }

    @Override
    public void onActivityResumed(Activity activity) {
        mActivity = new WeakReference<>(activity);
    }

    @Override
    public void onActivityPaused(Activity activity) {

    }

    @Override
    public void onActivityStopped(Activity activity) {
        appCount--;
    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

    }

    @Override
    public void onActivityDestroyed(Activity activity) {

    }

    /**
     * 判断当前APP是否在后台
     *
     * @param context
     * @return
     */
    public boolean inBackRunning(final Context context) {

        PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
        boolean isScreenOn = true;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT_WATCH) {
            isScreenOn = pm.isInteractive();
        } else {
            isScreenOn = pm.isScreenOn();
        }
        boolean isOnForeground = appCount > 0;
        return !isScreenOn || !isOnForeground;
    }

    /**
     * 获取当前页面的Fragment
     *
     * @return
     */
    public Fragment getCurFragment() {
        if (mActivity == null ||mActivity.get()==null|| !(mActivity.get() instanceof FragmentActivity)) {
            return null;
        }
        FragmentManager fragManager = ((FragmentActivity) mActivity.get()).getSupportFragmentManager();
        if (fragManager.getFragments() != null) {
            List<Fragment> fragments = fragManager.getFragments();
            for (Fragment fragment : fragments) {
                if (fragment != null && fragment.isVisible())
                    return fragment;
            }
            return null;
        }
        return null;
    }

    /**
     * 获取当前运行的Activity
     *
     * @return
     */
    public Activity getCurActivity() {
        return mActivity.get();
    }
}

/**
 *  页面顶部显示通知View实例 `[5]`
 **/
public class MessageBar extends FrameLayout {
    
        private Runnable mDismissRunnable = new Runnable() {
            @Override
            public void run() {
                dismiss();
            }
        };
    
    
        private AppMessage mAppMessage = new AppMessage.Builder().build();
    
        public MessageBar(Context context) {
            super(context);
        }
    
        public MessageBar(Context context, AttributeSet attrs) {
            super(context, attrs);
        }
    
        public MessageBar(Context context, AttributeSet attrs, int defStyle) {
            super(context, attrs, defStyle);
        }
    
        public static MessageBar with(Context context) {
            return new MessageBar(context);
        }
    
        public MessageBar setAppMessage(AppMessage appMessage) {
            if (appMessage != null) {
                mAppMessage = appMessage;
            }
            return this;
        }
    
        public void dismiss() {
            finish();
        }
    
        private void finish() {
            clearAnimation();
            ViewGroup parent = (ViewGroup) getParent();
            if (parent != null) {
                parent.removeView(this);
            }
        }
    
        /**
         * Displays the {@link MessageBar} at the bottom of the
         * {@link Activity} provided.
         *
         * @param targetActivity
         */
        public void show(Activity targetActivity) {
            ViewGroup root = (ViewGroup) targetActivity.findViewById(android.R.id.content);
            MarginLayoutParams params = init(targetActivity, root);
            showInternal(targetActivity, params, root);
            MediaUtil.getInstance(targetActivity).playSound(R.raw.im_notification, targetActivity);
            VibratorUtil.vibrator(targetActivity);
        }
    
        private MarginLayoutParams init(Activity targetActivity, ViewGroup parent) {
    
            FrameLayout layout = (FrameLayout) LayoutInflater.from(targetActivity)
                    .inflate(R.layout.mercury_template, this, true);
            customUI(layout);
            MarginLayoutParams params;
            params = createMarginLayoutParams(
                    parent, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
            return params;
        }
    
        private void customUI(FrameLayout layout) {
             //TODO init custom view 
        }
    
        private static MarginLayoutParams createMarginLayoutParams(ViewGroup viewGroup, int width, int height) {
            if (viewGroup instanceof FrameLayout) {
                LayoutParams params = new LayoutParams(width, height);
                params.gravity = TOP;
                return params;
            } else if (viewGroup instanceof RelativeLayout) {
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(width, height);
                params.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);
                return params;
            } else if (viewGroup instanceof LinearLayout) {
                LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(width, height);
                params.gravity = TOP;
                return params;
            } else {
                throw new IllegalStateException("Requires FrameLayout or RelativeLayout for the parent of Snackbar");
            }
        }
    
    
        private void showInternal(Activity targetActivity, MarginLayoutParams params, ViewGroup parent) {
    
            parent.removeView(this);
    
            // We need to make sure the MessageBar elevation is at least as high as
            // any other child views, or it will be displayed underneath them
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                for (int i = 0; i < parent.getChildCount(); i++) {
                    View otherChild = parent.getChildAt(i);
                    float elvation = otherChild.getElevation();
                    if (elvation > getElevation()) {
                        setElevation(elvation);
                    }
                }
            }
            parent.addView(this, params);
    
            bringToFront();
    
            // As requested in the documentation for bringToFront()
            if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) {
                parent.requestLayout();
                parent.invalidate();
            }
            focusForAccessibility(this);
            startTimer();
    
        }
    
        private void startTimer() {
            postDelayed(mDismissRunnable, 3000);
        }
    
    
        private void focusForAccessibility(View view) {
            final AccessibilityEvent event = AccessibilityEvent.obtain(AccessibilityEvent.TYPE_VIEW_FOCUSED);
    
            AccessibilityEventCompat.asRecord(event).setSource(view);
            try {
                view.sendAccessibilityEventUnchecked(event);
            } catch (IllegalStateException e) {
                // accessibility is off.
            }
        }
    
    
    }

参考

[1] 利用动态加载实现手机淘宝的节日特效：http://www.jianshu.com/p/195e...
[2] ActivityLifecycleCallbacks： https://developer.android.com...
[3] setContentView 背后那些事儿：http://www.jianshu.com/p/0219...
[4] android.R.id.content指什么以及一个实例：http://lingnanlu.github.io/20...
[5] snackbar：https://github.com/nispok/sna...