从零开始理解Android下View（一）----学习笔记（参考郭霖大神博客）

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我是靠谱客的博主勤奋板栗，这篇文章主要介绍从零开始理解Android下View（一）----学习笔记（参考郭霖大神博客），现在分享给大家，希望可以做个参考。

参考链接：郭神博客

Android下Activity中加载布局一般是通过setContentView()方法实现的，而setContentView()其实是通过调用LayoutInflater实现的。
要研究LayoutInflater原理，首先就要获取它的实例，有两种方法可以拿到LayoutInflater的实例:

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//第一种方法
LayoutInflater inflater = LayoutInflater.from(context);
//第二种方法
LayoutInflater inflater = context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

其中方法一相当于对方法二进行了一次封装。
inflater的基本使用就不在详细说，直接放通过LayoutInflater加载按钮的代码：

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public class MainActivity extends Activity {
 
	private LinearLayout mainLayout;
 
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		mainLayout = (LinearLayout) findViewById(R.id.main_layout);
		LayoutInflater layoutInflater = LayoutInflater.from(this);
		View buttonLayout = layoutInflater.inflate(R.layout.button_layout, null);
		mainLayout.addView(buttonLayout);
	}
 
}

可以看到LayoutInflater是通过调用inflater实现功能的，那么inflater()是如何实现的呢？
inflater()其实有多个重载，不过最终都会调用到下面这个实现：

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public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
    synchronized (mConstructorArgs) {
        final AttributeSet attrs = Xml.asAttributeSet(parser);
        mConstructorArgs[0] = mContext;
        View result = root;
        try {
            int type;
            while ((type = parser.next()) != XmlPullParser.START_TAG &&
                    type != XmlPullParser.END_DOCUMENT) {
            }
            if (type != XmlPullParser.START_TAG) {
                throw new InflateException(parser.getPositionDescription()
                        + ": No start tag found!");
            }
            final String name = parser.getName();
            if (TAG_MERGE.equals(name)) {
                if (root == null || !attachToRoot) {
                    throw new InflateException("merge can be used only with a valid "
                            + "ViewGroup root and attachToRoot=true");
                }
                rInflate(parser, root, attrs);
            } else {
                View temp = createViewFromTag(name, attrs);
                ViewGroup.LayoutParams params = null;
                if (root != null) {
                    params = root.generateLayoutParams(attrs);
                    if (!attachToRoot) {
                        temp.setLayoutParams(params);
                    }
                }
                rInflate(parser, temp, attrs);
                if (root != null && attachToRoot) {
                    root.addView(temp, params);
                }
                if (root == null || !attachToRoot) {
                    result = temp;
                }
            }
        } catch (XmlPullParserException e) {
            InflateException ex = new InflateException(e.getMessage());
            ex.initCause(e);
            throw ex;
        } catch (IOException e) {
            InflateException ex = new InflateException(
                    parser.getPositionDescription()
                    + ": " + e.getMessage());
            ex.initCause(e);
            throw ex;
        }
        return result;
    }
}

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public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
    synchronized (mConstructorArgs) {
        final AttributeSet attrs = Xml.asAttributeSet(parser);
        mConstructorArgs[0] = mContext;
        View result = root;
        try {
            int type;
            while ((type = parser.next()) != XmlPullParser.START_TAG &&
                    type != XmlPullParser.END_DOCUMENT) {
            }
            if (type != XmlPullParser.START_TAG) {
                throw new InflateException(parser.getPositionDescription()
                        + ": No start tag found!");
            }
            final String name = parser.getName();
            if (TAG_MERGE.equals(name)) {
                if (root == null || !attachToRoot) {
                    throw new InflateException("merge can be used only with a valid "
                            + "ViewGroup root and attachToRoot=true");
                }
                rInflate(parser, root, attrs);
            } else {
                View temp = createViewFromTag(name, attrs);
                ViewGroup.LayoutParams params = null;
                if (root != null) {
                    params = root.generateLayoutParams(attrs);
                    if (!attachToRoot) {
                        temp.setLayoutParams(params);
                    }
                }
                rInflate(parser, temp, attrs);
                if (root != null && attachToRoot) {
                    root.addView(temp, params);
                }
                if (root == null || !attachToRoot) {
                    result = temp;
                }
            }
        } catch (XmlPullParserException e) {
            InflateException ex = new InflateException(e.getMessage());
            ex.initCause(e);
            throw ex;
        } catch (IOException e) {
            InflateException ex = new InflateException(
                    parser.getPositionDescription()
                    + ": " + e.getMessage());
            ex.initCause(e);
            throw ex;
        }
        return result;
    }
}