看完郭神的解析后，我打算做一些简单的总结。一开始了解到的东西是LayoutInflate，既然是源码分析，那就得先能查看源码，查看源码的方法是打开你的Android Studio点击File -》Setting -》搜索框中搜索Android SDK -》Show Package Details -》下载source for Android 23（因为我手机是安卓6.0版本我就习惯性的下了6.0的源码，最好还是下最新版本的源码）
先来研究的东西是LayoutInflate：
不管你用哪个inflate方法的重载你都会转到inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)中
public View inflate(XmlPullParser parser, @Nullable ViewGroup root,boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW,"inflate");
final Context inflaterContext =mContext;
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context)mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
View result = root;
try {
// Look for the root node.
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+": No start tag found!");
}
final String name = parser.getName();
if (DEBUG) {
System.out.println("**************************");
System.out.println("Creating root view: "
+ name);
System.out.println("**************************");
}
if (TAG_MERGE.equals(name)) {
if (root ==null || !attachToRoot) {
throw new InflateException(" 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) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// 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);
}
}
if (DEBUG) {
System.out.println("-----> start inflating children");
}
// Inflate all children under temp against its context.
rInflateChildren(parser, temp, attrs,true);
if (DEBUG) {
System.out.println("-----> done inflating children");
}
// 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) {
final InflateException ie =new InflateException(e.getMessage(), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
}catch (Exception e) {
final InflateException ie =new InflateException(parser.getPositionDescription()
+": " + e.getMessage(), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
}finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] =null;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
return result;
}
}
可以看到他先用pull解析方式来解析xml文件，再通过createViewFromTag()把参数传给他，你要是在点进去查看该方法你就可以知道它是用createView()来创建并返回一个View的实例的，再通过rInflate()查找view下的子元素并逐一添加进父布局中，随着版本更新迭代，源码中多了一个rInflateChildren()，实际上他也调用了rInflate()，这样做的目的是填充所有子布局。
我们在调用setContentView()时，Android会自动在布局文件的最外层再嵌套一个帧布局，如果没有外面套着的这一层布局就无法设置该布局的width和height