走了一遍 LayoutInflater的流程，特此记录
获取 LayoutInflater --- LayoutInflater.from(context)
获取LayoutInflater对象实例
public static LayoutInflater from(Context context) {
//获取 layoutInflater，注意这是一个IPC的过程，获取的实例是PhoneLayoutInflater，与LayoutInflater 区别不大，重写了protected View onCreateView(String name, AttributeSet attrs) 函数，具体可以去看源码，位置是frameworks/base/core/java.com.android.internal.policy.impl
LayoutInflater LayoutInflater =
(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
//如果为空抛出错误
if (LayoutInflater == null) {
throw new AssertionError("LayoutInflater not found.");
}
//返回值
return LayoutInflater;
}
调用Inflate -- LayoutInflater.from(context).inflate(R.layout.activity_layout,null,false)
public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
//获取resource对象
final Resources res = getContext().getResources();
...
//把R.layout.activity_layout 放入，获取整个 Xml的Parser
final XmlResourceParser parser = res.getLayout(resource);
try {
// 开始真正的inflate
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)是整个inflate的核心部分
整体流程：
找到最外层的父级布局 ===》 处理merge节点情况 ===》实例化父级布局 ===》根据父级布局，调用rInflate函数去实例化子级view ===> 根据实例化结果，以及外部参数，进行view的添加以及结果的返回
public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
//同步进入
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
// 解析返回 attrs
final AttributeSet attrs = Xml.asAttributeSet(parser);
//
Context lastContext = (Context)mConstructorArgs[0];
mConstructorArgs[0] = mContext;
// 传入的 viewgroup 是 null
View result = root;
try {
// 此处尝试寻找开始和结束节点，即找到整个layout的最外层 view
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
// 如果 type != 开始节点抛出错误，也就是说没找到开始节点
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
* ": No start tag found!");
}
// 获取当前节点的名字，也就是当前layout的根节点的名字
final String name = parser.getName();
...
//处理 merge 节点
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, false, false);
} else {// 不是merge的情况下
// createViewFromTag 该方法是根据前面获取的 tag 的名字，创建具体的view对象
// 此处特殊的地方时，Temp 就是根节点，也就是整个layout的根节点，因为 name 是前面获取的根节点的名字
final View temp = createViewFromTag(root, name, attrs, false);
// 初始化 params
ViewGroup.LayoutParams params = null;
if (root != null) {// root != 空，会初始化出一个 params
...
// 如果提供了root，会根据 root 创建 layout params
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);
}
}
...
// 此处，会进行所有的 temp 的子 view 的 inflate
rInflate(parser, temp, attrs, true, 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) {
...
} catch (IOException e) {
...
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
return result;
}
}
其中整个流程中，核心部分分两点
1.实例化父级布局，
2.实例化子级view。
而对于merge节点的处理情况是将其当做子view进行处理，调用的都是rInflate函数，所以，我们讨论子view实例化的时候可以一起讨论。
首先是看第一部分，父布局temp的实例化。
他是直接调用createViewFromTag，我们进入该函数。这个函数整体的流程是
处理特殊节点view ===》 对当前view的context进行初始化 ====》 特殊节点blink处理 ===》根据几个工厂对象(默认情况下，工程类都为null)实例化view ===》 工厂类创建失败，view == null，调用onCreateView()或者createView()对view进行实例化
View createViewFromTag(View parent, String name, AttributeSet attrs, boolean inheritContext) {
// 特殊处理 `view` 节点
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
// 设置当前 view 的 context
Context viewContext;
if (parent != null && inheritContext) {
// 如果父级 view 不为空 并且要求从父级 view 那里获取 context
viewContext = parent.getContext();
} else {
// 否则 当前 view 的 context 等于 LayoutInflater.fromt(context) 中传入的 context
viewContext = mContext;
}
// 如果有主题切换，那么就应用对应的主题
final TypedArray ta = viewContext.obtainStyledAttributes(attrs, ATTRS_THEME);
final int themeResId = ta.getResourceId(0, 0);
if (themeResId != 0) {
viewContext = new ContextThemeWrapper(viewContext, themeResId);
}
ta.recycle();
// blink 处理
if (name.equals(TAG_1995)) {
// Let's party like it's 1995!
return new BlinkLayout(viewContext, attrs);
}
...
try {
// 用工厂类创建真正的 view 对象
// 默认两个工厂类都为 null
// 所以 view 是 null
View view;
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, viewContext, attrs);
} else if (mFactory != null) {
view = mFactory.onCreateView(name, viewContext, attrs);
} else {
view = null;
}
// 在 view 用前面两个工厂类创建为 null
// 同时私有工厂类不为空的情况下，调用私有的工厂类创建 view 对象
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, viewContext, attrs);
}
// 私有工厂创建依旧为 null 时
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = viewContext;
try {
if (-1 == name.indexOf('.')) {// 如果是 Android 自带 view
view = onCreateView(parent, name, attrs);
} else {// 如果不是 Android 自带 view
view = createView(name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
...
return view;
} catch (InflateException e) {
...
} catch (ClassNotFoundException e) {
...
} catch (Exception e) {
...
}
}
其中这个函数的核心部分则是onCreateView()和createView()，因为默认情况下，几个factory都是null，所以都会进入这两个函数中的一个。
if (-1 == name.indexOf('.')) {// 如果是 Android 自带 view
view = onCreateView(parent, name, attrs);
} else {// 如果不是 Android 自带 view
view = createView(name, null, attrs);
}
两个函数调用条件是，-1 == name.indexOf('.')，而其效果则是，判断是否为Android自带 view，如果是，则调用onCreateView(),否则当做自定义view处理，调用createView()
先看onCreateView，该部分主要是对sClassPrefixList进行迭代，拼凑出整个view的路径，然后调用createView()，注意这个函数，和上面说的处理自定义view的createView()，是同一个函数，所以也就明白，为什么要有上面的判断了
private static final String[] sClassPrefixList = {
"android.widget.",
"android.webkit.",
"android.app."
};
....
....
@Override protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
for (String prefix : sClassPrefixList) {
try {
View view = createView(name, prefix, attrs);
if (view != null) {
return view;
}
} catch (ClassNotFoundException e) {
...
}
}
return super.onCreateView(name, attrs);
}
然后我们看真正的动态创建出view对象的函数createView(String name, String prefix, AttributeSet attrs)，该函数的作用就是，通过反射创建出真正的对象
其过程也很简单，直接在已经存在的sConstructorMap中找，是不是有这个名字，如果有就开始创建，没有就把前缀拼上去，再创建，然后放入sConstructorMap中
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
Constructor<? extends View> constructor = sConstructorMap.get(name);
Class<? extends View> clazz = null;
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);
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);
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[] args = mConstructorArgs;
args[1] = attrs;
constructor.setAccessible(true);
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]));
}
return view;
} catch (NoSuchMethodException e) {
...
} catch (ClassCastException e) {
...
} catch (ClassNotFoundException e) {
...
} catch (Exception e) {
...
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
然后是子布局的实例化
该部分内容，主要是对当前节点的所有view 进行遍历，然后调用createViewFromTag()(该方法上面已经有解释了)方法创建实例。如果遍历到某一个view，他是有子节点的，则递归调用函数rInflate()对该子节点进行遍历。该部分参考下面的流程图，看起来更加清晰。
void rInflate(XmlPullParser parser, View parent, final AttributeSet attrs,
boolean finishInflate, boolean inheritContext) throws XmlPullParserException,
IOException {
final int depth = parser.getDepth();
int type;
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)) {
parseRequestFocus(parser, parent);
} 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, parent, attrs, inheritContext);
} else if (TAG_MERGE.equals(name)) {
throw new InflateException("<merge /> must be the root element");
} else {
final View view = createViewFromTag(parent, name, attrs, inheritContext);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
rInflate(parser, view, attrs, true, true);
viewGroup.addView(view, params);
}
}
if (finishInflate) parent.onFinishInflate();
}
===========================
以上就是 inflate 整个核心部分。
对于整体的流程，我画了流程图，如下
LayoutInflater流程.png
原稿是mind node做的，需要的私信，或者留言
