`上一节:安卓 - 源码分析 - LayoutInflater(一)
inflate方法的重载:
inflate方法有很多重载,而最终将会进入:
/*
* 3个参数分别为:
* parser : 已经包含xml布局的xml解析器
* root : 可选参数,生成的布局的根视图,作用取决于attachToRoot参数
* attachToRoot : 当为true时,生成的View作为子控件添加到根视图root;
当为false时,root仅为生成的View提供外部的LayoutParams;
*/
public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)
当调用参数为xml资源id的重载方法时:
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot)
则会使用getResources().getLayout(resource)将xml布局资源转换为XmlResourceParser:
final XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
默认的attachToRoot由root参数是否null决定:
public View inflate(XmlPullParser parser, @Nullable ViewGroup root){
return inflate(parser, root, root != null);
}
inflate的过程:
解析过程,只需要关注最终使用的inflate方法。去掉Debug和Trace,取出关键的源码先大概了解:
public View inflate(XmlPullParser parser, @Nullable 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 {
int type;
//Look for the root node.
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, 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);
}
}
// Inflate all children under temp against its context.
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 (Exception e) {
...
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
}
return result;
}
}
应该已经很明显了,然后我们一步步分析:
/*
* 这里主要做了一些关键对象的配置和临时保存。
*/
final Context inflaterContext = mContext;
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
View result = root;
/*
* 这里主要检索xml是否能够被解析。
* 查找第一个标签,直到文件结束。
* 一个标签都找不到时,抛出异常,结束解析。
*/
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!");
}
/*
* 这里主要是为xml布局文件创建一个根节点,
*/
if (TAG_MERGE.equals(name)) {
/*
* 当标签是merge时,必须有父布局及需要添加到父布局,否则异常
*/
if (root == null || !attachToRoot) {
throw new InflateException("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
/*
* 当第一个标签是<merge/>时,调用rInflate方法解析xml并填充到参数给出的root
* rInflate方法后面介绍
*/
rInflate(parser, root, inflaterContext, attrs, false);
} else {
/*
* 当第一个标签不是merge时,使用这个标签创建一个根节点temp,
* 调用createViewFromTag方法创建View,这个方法后面介绍
*/
final String name = parser.getName();
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
/* 这里的流程下面介绍 */
...
}
/*
* 根据root和attachToRoot,为根节点temp配置合适的LayoutParams。
*/
ViewGroup.LayoutParams params = null;
if (root != null) {
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
temp.setLayoutParams(params);
}
}
/*
* 通过rInflateChildren方法,将剩余的子节点解析并填充到根节点temp
* rInflateChildren方法后面介绍
*/
rInflateChildren(parser, temp, attrs, true);
/*
* 这时根节点temp已经解析完毕,并已正确添设置LayoutParams,
* 如果参数root非空,且参数attachToRoot为true,则将temp添加到root上
*/
if (root != null && attachToRoot) {
root.addView(temp, params);
}
/*
* 在开始的时候,result被设置为root,
* 当root为空,或者attachToRoot为false,即temp没有被添加到root时
* 应该将temp作为结果返回,即把result设置为temp
*/
if (root == null || !attachToRoot) {
result = temp;
}
/* 清空context引用 */
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
/* 返回结果 */
return result;
inflate过程调用的几个重要方法:
rInflate方法:
例行先源码,删减部分
void rInflate(XmlPullParser parser, View parent, Context context,
AttributeSet attrs, boolean finishInflate)
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, 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 (finishInflate) {
parent.onFinishInflate();
}
}
进一步分析:
/*
* 这里获取了xml的当前层,用于后面的层次校验,
* 保证while循环于当前节点内,例如:
* 当前层为1,当循环到层1时,表示当前节点的子节点全部解析完成
*/
final int depth = parser.getDepth();
int type;
/*
* 循环条件为:
* 层次深于当前层的节点的结尾(即不为当前节点的结尾)并且不为文件结尾
* 这样确保了解析所有子节点,直到文件结尾,或子节点解析完成
*/
while (((type = parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > depth)
&& type != XmlPullParser.END_DOCUMENT) {
/*
* 确保从节点开始解析节点
*/
if (type != XmlPullParser.START_TAG) {
continue;
}
/* 这里的流程下面介绍 */
...
}
/*
* 根据不同的标签进行不同的处理,主要针对几个特殊标签:
* <requestFocus/>:使用在非容器View内,能使View获取焦点
* <tag/> :能在xml进行Tag设置,相当于setTag(id, value)
* <include/> :include只能作为子节点使用
* <merge/> :merge只能作为根节点使用
* 具体的parse相对简单,可以自行了解
* 而不是这几个特殊标签时,进入正常解析流程
*/
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, context, parent, attrs);
} else if (TAG_MERGE.equals(name)) {
throw new InflateException("<merge /> must be the root element");
} else {
/*
* 正常解析流程,看得出这个流程使用了递归算法
* 调用createViewFromTag,生成当前标签对应的View对象,
* 然后通过其父容器得到LayoutParams,
* 然后调用rInflateChildren对该节点下的子节点进行解析填充,
* 最后,将这个View添加到父容器中。
*/
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);
}
rInflateChildren方法:
/*
* 不做过多解析,看得出,rInflateChildren只是对rInflate的简单封装
*/
final void rInflateChildren(XmlPullParser parser, View parent,
AttributeSet attrs,boolean finishInflate)
throws XmlPullParserException, IOException {
rInflate(parser, parent, parent.getContext(), attrs, finishInflate);
}
createViewFromTag方法:
View createViewFromTag(View parent, String name, Context context,
AttributeSet attrs, boolean ignoreThemeAttr) {
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
if (!ignoreThemeAttr) {
final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
final int themeResId = ta.getResourceId(0, 0);
if (themeResId != 0) {
context = new ContextThemeWrapper(context, themeResId);
}
ta.recycle();
}
if (name.equals(TAG_1995)) {
return new BlinkLayout(context, attrs);
}
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;
}
}
return view;
} catch (Exception e) {
...
}
}
这里就涉及到分析一提及到的Factory了,继续慢慢分析:
/*
* 对于<view/>标签,取出其class属性替代标签名称
*/
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
// 这里会产生一个问题,什么是view标签,class属性又是什么
// 其实view标签是为内部类View使用的,例如:
// 在com.example.A.class里,有一个自定义View:ViewB.class,
// 在编译后,ViewB类名则变成了com.example.A.class$ViewB,
// 而<com.example.A$ViewB/>标签是不能定义的,所以就要使用到<view/>标签
// 即<view class="com.example.A$ViewB"/>
// 当然你也可以对普通的View使用同样的定义方法如<view class="Button"/>
// 注意,使用<view/>标签必须定义class,否则会抛空指针异常
/*
* 处理主题相关
*/
if (!ignoreThemeAttr) {
final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
final int themeResId = ta.getResourceId(0, 0);
if (themeResId != 0) {
context = new ContextThemeWrapper(context, themeResId);
}
ta.recycle();
}
/*
* 这个TAG_1995其实就是<blink/>标签
* 会为这个标签创建一个BlinkLayout直接返回
* 这个BlinkLayout,会对内部的控件提供一种闪烁的功能
* 然而是没什么卵用的,其实就是内部维护了一个handler,
* 每0.5秒进行一次更新,根据mBlinkState去选择性绘制子控件
* 这个0.5秒是个final值,不能改变
*/
if (name.equals(TAG_1995)) {
return new BlinkLayout(context, attrs);
}
/*
* 这里就是View的创建位置,调用优先级为:
* 自定义Factory > 系统Factory > LayoutInflater默认
*/
try {
View view;
if (mFactory2 != null) {
/*
* 优先使用Factory2
*/
view = mFactory2.onCreateView(parent, name, context, attrs);
} else if (mFactory != null) {
/*
* 然后再是Factory
*/
view = mFactory.onCreateView(name, context, attrs);
} else {
view = null;
}
/* 这里的流程下面介绍 */
...
}
/*
* 没有设置自定义Factory时,尝试使用系统添加的Factory进行创建
*/
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs);
}
/*
* 没有设置任何工厂时,使用默认的createView方法创建View
*/
if (view == null) {
/*
* 这里也是临时记录context
*/
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
/*
* 这里其实就是看你的view有没有完整的类名
* 类似Button,那么就是不完整,使用onCreateView
* 类似com.example.ViewA这样的,就可以直接使用createView
*/
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
} finally {
/*
* 还原临时记录
*/
mConstructorArgs[0] = lastContext;
}
}
// 返回View
return view;
onCreateView方法:
/*
* 这个方法就是对系统提供的控件补完类名"android.view."
* 实际上工作的还是createView方法
*/
protected View onCreateView(String name, AttributeSet attrs)
throws ClassNotFoundException {
return createView(name, "android.view.", attrs);
}
createView方法:
还是先贴源码,在这个createView里面,涉及到我们之前说的Filter了,直接解析流程
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
/*
* 尝试从构造器缓存取出构造器
*/
Constructor<? extends View> constructor = sConstructorMap.get(name);
Class<? extends View> clazz = null;
try {
if (constructor == null) {
/*
* onCreateView方法的"android.view."在这里拼接
* prefix + name
*/
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
/*
* 这里就是Filter作出过滤的地方了
* 不通过过滤就会通过failNotAllowed排除异常
*/
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
}
/*
* 找不到构造缓存,就在这里查找一次,并放入缓存
*/
constructor = clazz.getConstructor(mConstructorSignature);
constructor.setAccessible(true);
sConstructorMap.put(name, constructor);
} else {
/*
* 有构造器缓存的话,直接使用Filter做一次过滤
* 这里做了个优化,缓存了Filter的过滤结果
*/
if (mFilter != null) {
// 查找Filter缓存
Boolean allowedState = mFilterMap.get(name);
if (allowedState == null) {
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
// 插入Filter缓存
mFilterMap.put(name, allowed);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
} else if (allowedState.equals(Boolean.FALSE)) {
failNotAllowed(name, prefix, attrs);
}
}
}
/*
* 到了这里就知道mConstructorArgs对象里面存放的是什么
* 分别是context和attrs,老铁,没毛病
*/
Object[] args = mConstructorArgs;
args[1] = attrs;
/*
* newInstance了,反射,没毛病
*/
final View view = constructor.newInstance(args);
/*
* 像是ViewStub这样的情况
* 则将自己(LayoutInflater)复制一份给ViewStub
* 延迟加载
*/
if (view instanceof ViewStub) {
final ViewStub viewStub = (ViewStub) view;
viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
}
/*
* 到这里终于结束这个创建流程了
*/
return view;
} catch (NoSuchMethodException e) {
...
}
}
上面整个流程涉及到的几个点需要说一下:
Filter和Factory:
因为Filter的调用是在LayoutInflater的默认创建过程才会调用的,如果拦截的View在Factory中被返回,则Filter是不会起效的,你也可以在Factory中自行调用Filter进行拦截判断。
创建子节点和本节点:
所有的创建本节点,都是使用createViewFromTag方法,
某一个节点的子节点创建,都是使用了rInflateChildren方法。
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