本文主要是自己对LayoutInflater 使用的相关总结

我们经常实用的LayoutInflater这样用：

View view = LayoutInflater.from(context).inflate(R.layout.resource,root,flase);

进入inflate进行源码解析

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public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
    final Resources res = getContext().getResources();
    if (DEBUG) {
        Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
                + Integer.toHexString(resource) + ")");
    }
    final XmlResourceParser parser = res.getLayout(resource);
    try {
        return inflate(parser, root, attachToRoot);
    } finally {
        parser.close();
    }
}

主要做了一件事：
建立XmlResourceParser为后面解析xml文件做准备
XmlResourceParser的解析原理可以去这里看看

继续进入inflate(为方便阅读删除一些调试代码和异常捕获代码，只保留了核心代码)

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public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
    synchronized (mConstructorArgs) {
        final Context inflaterContext = mContext;
        final AttributeSet attrs = Xml.asAttributeSet(parser);
        Context lastContext = (Context) mConstructorArgs[0];
        mConstructorArgs[0] = inflaterContext;
        View result = root;
        try {
            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, inflaterContext, attrs, false);
            } else {
                // Temp is the root view that was found in the xml
                final View temp = createViewFromTag(root, name, inflaterContext, attrs);
                ViewGroup.LayoutParams params = null;
                if (root != null) {
                    // Create layout params that match root, if supplied
                    params = root.generateLayoutParams(attrs);
                    if (!attachToRoot) {
                        // Set the layout params for temp if we are not
                        // attaching. (If we are, we use addView, below)
                        temp.setLayoutParams(params);
                    }
                }
                rInflateChildren(parser, temp, attrs, true);
                // We are supposed to attach all the views we found (int temp)
                // to root. Do that now.
                if (root != null && attachToRoot) {
                    root.addView(temp, params);
                }
                // Decide whether to return the root that was passed in or the
                // top view found in xml.
                if (root == null || !attachToRoot) {
                    result = temp;
                }
            }
        } catch (XmlPullParserException e) {...}

这段源码中看出主要逻辑为：

1、判断xml局中标签是否为merge,如果是则走rInflate直接去遍历创建xml所有的View对象

2、进入非merge的逻辑里面，会创建根View，主要的过程在createViewFromTag创建View

3、rInflateChildren创建子View

3、接下来如果传入的root不为null,并且attachToRoot==false，则对创建好的View的ViewGroup.LayoutParams是通过generateLayoutParams生成的。

4、如果root不为null,attachToRoot==true，那么则将整个View作为一个子View加入到父布局中，否则直接返回这个View

继续进入createViewFromTag源码（为方便理解去除异常彩蛋和ignoreThemeAttr属性的代码）

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View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
        boolean ignoreThemeAttr) {
    if (name.equals("view")) {
        name = attrs.getAttributeValue(null, "class");
    }
    try {
        View view;
        if (mFactory2 != null) {
            view = mFactory2.onCreateView(parent, name, context, attrs);
        } else if (mFactory != null) {
            view = mFactory.onCreateView(name, context, attrs);
        } else {
            view = null;
        }
        if (view == null && mPrivateFactory != null) {
            view = mPrivateFactory.onCreateView(parent, name, context, attrs);
        }
        if (view == null) {
            final Object lastContext = mConstructorArgs[0];
            mConstructorArgs[0] = context;
            try {
                if (-1 == name.indexOf('.')) {
                    view = onCreateView(parent, name, attrs);
                } else {
                    view = createView(name, null, attrs);
                }
            } finally {
                mConstructorArgs[0] = lastContext;
            }
        }
		……

这段源码中看出主要逻辑为：

1、标签为view时获取view的class属性作为要创建的View的name(注意View和view的区别)

2、主要通过不同的Factory通过**createView() **去创建View

3、其中有个逻辑需要在onCreateView执行之前判断是否存在“.”，存在点则表示不是系统的View,需要单独处理，在后面createView的代码可以看到有这样一段加入了“android.view.”，后面会讲这句的用途。

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protected View onCreateView(String name, AttributeSet attrs)
        throws ClassNotFoundException {
    return createView(name, "android.view.", attrs);
}

继续进入onCreateView源码

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public final View createView(String name, String prefix, AttributeSet attrs)
        throws ClassNotFoundException, InflateException {
    Constructor<? extends View> constructor = sConstructorMap.get(name);
    if (constructor != null && !verifyClassLoader(constructor)) {
        constructor = null;
        sConstructorMap.remove(name);
    }
    Class<? extends View> clazz = null;
    try {
        if (constructor == null) {
            // Class not found in the cache, see if it's real, and try to add it
            clazz = mContext.getClassLoader().loadClass(
                    prefix != null ? (prefix + name) : name).asSubclass(View.class);

            if (mFilter != null && clazz != null) {
                boolean allowed = mFilter.onLoadClass(clazz);
                if (!allowed) {
                    failNotAllowed(name, prefix, attrs);
                }
            }
            constructor = clazz.getConstructor(mConstructorSignature);
            constructor.setAccessible(true);
            sConstructorMap.put(name, constructor);
        } else {
            // If we have a filter, apply it to cached constructor
            if (mFilter != null) {
                // Have we seen this name before?
                Boolean allowedState = mFilterMap.get(name);
                if (allowedState == null) {
                    // New class -- remember whether it is allowed
                    clazz = mContext.getClassLoader().loadClass(
                            prefix != null ? (prefix + name) : name).asSubclass(View.class);

                    boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
                    mFilterMap.put(name, allowed);
                    if (!allowed) {
                        failNotAllowed(name, prefix, attrs);
                    }
                } else if (allowedState.equals(Boolean.FALSE)) {
                    failNotAllowed(name, prefix, attrs);
                }
            }
        }
        Object lastContext = mConstructorArgs[0];
        if (mConstructorArgs[0] == null) {
            // Fill in the context if not already within inflation.
            mConstructorArgs[0] = mContext;
        }
        Object[] args = mConstructorArgs;
        args[1] = attrs;
        final View view = constructor.newInstance(args);
        if (view instanceof ViewStub) {
            // Use the same context when inflating ViewStub later.
            final ViewStub viewStub = (ViewStub) view;
            viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
        }
        mConstructorArgs[0] = lastContext;
        return view;
    }

​
这段源码虽然很复杂，但主要做的事就是 通过反射的方式去加载一个View类

这段代码就能解释上面为什么要加“android.view.”，这段代码会将系统的View的路径拼起来，把类加载进来；

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clazz = mContext.getClassLoader().loadClass(prefix != null ? (prefix + name) : name).asSubclass(View.class)

到现在，我们讲完了对于xml根view的创建逻辑，还有个很重要的流程没有讲：

子View创建 的逻辑在inflate中的rInflateChildren

进入rInflateChildren，这里依然会进入到rInflate()

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 void rInflate(XmlPullParser parser, View parent, Context context,
        AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {

    final int depth = parser.getDepth();
    int type;
    boolean pendingRequestFocus = false;
    while (((type = parser.next()) != XmlPullParser.END_TAG ||
            parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
        if (type != XmlPullParser.START_TAG) {
            continue;
        }
        final String name = parser.getName();
        if (TAG_REQUEST_FOCUS.equals(name)) {
            pendingRequestFocus = true;
            consumeChildElements(parser);
        } else if (TAG_TAG.equals(name)) {
            parseViewTag(parser, parent, attrs);
        } else if (TAG_INCLUDE.equals(name)) {
            if (parser.getDepth() == 0) {
                throw new InflateException("<include /> cannot be the root element");
            }
            parseInclude(parser, context, parent, attrs);
        } else if (TAG_MERGE.equals(name)) {
            throw new InflateException("<merge /> must be the root element");
        } else {
            final View view = createViewFromTag(parent, name, context, attrs);
            final ViewGroup viewGroup = (ViewGroup) parent;
            final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
            rInflateChildren(parser, view, attrs, true);
            viewGroup.addView(view, params);
        }
    }
    if (pendingRequestFocus) {
        parent.restoreDefaultFocus();
    }
    if (finishInflate) {
        parent.onFinishInflate();
    }
}

这段源码的大致可以总结为：

1、总的逻辑为获取xml文档的层级数，解析每一层级的数据

2、解析过程首先进行View的合理性校验，include、merge等标签；

3、最后还是会走到createViewFromTag 创建出 View 对象，如果是 ViewGroup则递归调用rInflateChildren

到这里基本上所有的流程讲完了，这里总结一下加载流程：

1、拿到Xml解析对象，为后续解析做准备

2、对整个Xml中的布局控制处理由 root、attachToRoot这两个参数控制

3、解析子View，通过createViewFromTag创建实例对象**