LayoutInflater是加载布局的,它是把布局文件转变成View对象,获取LayoutInflater实例对象,一般有二种方法
1：LayoutInflater layoutInflater = LayoutInflater.from(context);
2：LayoutInflater layoutInflater = (LayoutInflater) context .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
我们进入源码分析下：
/**
* Obtains the LayoutInflater from the given context.
*/
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;
}这源码很简单,一眼就看出其实LayoutInflater.from(Context)是对其
LayoutInflater LayoutInflater =
(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);方法的封装,所以这二个方法随便使用那个都是一样的,知道这个类是怎么来的,那么看下它是怎么把一个layout转变成一个View对象的,我们在Adapter中的getView()方法中都是要使用到LayoutInflater对象,是通过inflater()这个方法把layout变成View对象的,那么就进入这个方法看源码是如何实现的,进入源码：
public View inflate(XmlPullParser parser, ViewGroup root) {
return inflate(parser, root, root != null);
}我们进入inflater方法继续查看，
public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context)mConstructorArgs[0];
mConstructorArgs[0] = mContext;
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("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
rInflate(parser, root, attrs, false);
} else {
// Temp is the root view that was found in the xml
View temp;
if (TAG_1995.equals(name)) {
temp = new BlinkLayout(mContext, attrs);
} else {
temp = createViewFromTag(root, name, 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
rInflate(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) {
InflateException ex = new InflateException(e.getMessage());
ex.initCause(e);
throw ex;
} catch (IOException e) {
InflateException ex = new InflateException(
parser.getPositionDescription()
+ ": " + e.getMessage());
ex.initCause(e);
throw ex;
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
}
return result;
}
}从源码中我们发现,在android源码中解析xml是通过pull解析的,通过进一步分析,发现有一个重要的方法：
View createViewFromTag(View parent, String name, AttributeSet attrs)它返回的是View对象,
View view;
if (mFactory2 != null) view = mFactory2.onCreateView(parent, name, mContext, attrs);
else if (mFactory != null) view = mFactory.onCreateView(name, mContext, attrs);
else view = null;
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, mContext, attrs);
}
if (view == null) {
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
}这段代码是创建View对象的,它调用的都是onCreateView()返回view的,那么layout那么多控件,肯定不止创建一个View对象,肯定是有个while或者for循环创建一系列的view，然后把这些view对象添加到根View对象中,那好我们再沿着这条思路去查找答案,还是到inflater方法中找,发现有rInflate()方法,
void rInflate(XmlPullParser parser, View parent, final 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_INCLUDE.equals(name)) {
if (parser.getDepth() == 0) {
throw new InflateException("<include /> cannot be the root element");
}
parseInclude(parser, parent, attrs);
} else if (TAG_MERGE.equals(name)) {
throw new InflateException("<merge /> must be the root element");
} else if (TAG_1995.equals(name)) {
final View view = new BlinkLayout(mContext, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
<span style="color:#ff0000;"> rInflate(parser, view, attrs, true);</span>
viewGroup.addView(view, params);
} else {
final View view = createViewFromTag(parent, name, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
<span style="color:#ff6666;"> rInflate(parser, view, attrs, true);</span>
viewGroup.addView(view, params);
}
}
if (finishInflate) parent.onFinishInflate();
}这个rflater是个递归方法,不断的把view添加到父控件View中
viewGroup.addView(view, params);这行代码就是添加子view到父控件上,
源码分析到这了,现在看一个小的细节,就是每个activity中都会设置setContextView，我们通过eclipse的ddms工具分析下他的布局,布局很简单就一个textview,
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
看下它的布局,
我们发现它的根布局是Framelayout,我们发现FrameLayout是由标题布局和内容布局构成的,FrameLayout下面的油一个LinearLayout布局,然后它有2个子控件,2个都是FrameLayout，一个FrameLayout是标题栏,一个FrameLayout就是我们layout显示的内容了,所有google在activity中的setContextView()就是设置我们layout的布局,从这名字就可以看出,google方法名设置的多好
扫一扫
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
