一、概述
我们平常创建view一般是使用View view = LayoutInflate.from(context).inflate(resId, parent）来创建。通过阅读源码可以让我们了解view的创建过程。
二、源码解析
1.先来看from方法：
public static LayoutInflater from(Context context) {
LayoutInflater LayoutInflater =
(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (LayoutInflater == null) {
throw new AssertionError("LayoutInflater not found.");
}
return LayoutInflater;
}
这里我们知道通过LayoutInflate其实是系统的一项服务。
2.看下inflate方法：
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;
//解析XML的根标签。
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("**************************");
}
//如果是merge，调用rInflate进行解析。它会把merge所有子view添加到根标签中。
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 {
//如果是普通标签，调用createViewFromTag进行解析。
// 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");
}
//用rInflate解析temp根元素下的子view。并添加到temp中。
// 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);
}
//最后返回root
return result;
}
}
这里我们知道解析xml使用的是pull解析，Android其实一共有三种解析方式：dom、sax、pull解析，Android中解析xml使用pull，解析textview.fromHtml()中的html使用sax中的tagSoup。
3.其实我们主要看下createViewFromTag()这个方法就可以:
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
//此处省略一些代码，减少眼疲劳
............
try {
View view;
//前方高能！高能！高能！
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 (InflateException e) {
throw e;
} catch (ClassNotFoundException e) {
..........
}
}
4.我们知道了view的创建都是通过Factory来创建的。我们来看下factory是如何创建的：
@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
View view = null;
if (view == null) {
view = createViewOrFailQuietly(name,context,attrs);
}
return view;
}
private View createViewOrFailQuietly(String name, Context context,
AttributeSet attrs) {
//1.自定义控件标签名称带点，所以创建时不需要前缀
if (name.contains(".")) {
createViewOrFailQuietly(name, null, context, attrs);
}
//2.系统视图需要加上前缀
for (String prefix : sClassPrefix) {
View view = createViewOrFailQuietly(name, prefix, context, attrs);
if (view != null) {
return view;
}
}
return null;
}
createViewOrFailQuietly会判断是不是自定义布局，有点的是自定义布局，没有点的需要改成全路径的形式。
5.最后其实是通过inflate的createView来创建view。
private View createViewOrFailQuietly(String name, String prefix, Context context,
AttributeSet attrs) {
try {
//通过系统的inflater创建视图，读取系统的属性
return inflater.createView(name, prefix, attrs);
} catch (Exception e) {
return null;
}
}
到此源码分析完毕！！！
三、总结
inflate通过pull解析的方式获取到每个view的标签，之后通过factory将标签转换成view。整个流程还是比较简单的。
四、反思
阅读源码之后我们知道：其实可以自定义factory来创建view，自定义factory中可以对view做一些额外的处理。
