ViewStub延迟加载

 public View inflate() {
        final ViewParent viewParent = getParent();
 
        if (viewParent != null && viewParent instanceof ViewGroup) {
            if (mLayoutResource != 0) {
                final ViewGroup parent = (ViewGroup) viewParent;
                final LayoutInflater factory;
                if (mInflater != null) {
                    factory = mInflater;
                } else {
                    factory = LayoutInflater.from(mContext);
                }
                final View view = factory.inflate(mLayoutResource, parent,
                        false);
 
                if (mInflatedId != NO_ID) {
                    view.setId(mInflatedId);
                }
 
                final int index = parent.indexOfChild(this);
                parent.removeViewInLayout(this);
 
                final ViewGroup.LayoutParams layoutParams = getLayoutParams();
                if (layoutParams != null) {
                    parent.addView(view, index, layoutParams);
                } else {
                    parent.addView(view, index);
                }
 
                mInflatedViewRef = new WeakReference<View>(view);
 
                if (mInflateListener != null) {
                    mInflateListener.onInflate(this, view);
                }
 
                return view;
            } else {
                throw new IllegalArgumentException("ViewStub must have a valid layoutResource");
            }
        } else {
            throw new IllegalStateException("ViewStub must have a non-null ViewGroup viewParent");
        }
    }

<LinearLayout 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"
    android:orientation="vertical"
    tools:context="com.example.viewstub.MainActivity" >
 
    <Switch
        android:id="@+id/switch1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
 
    <ViewStub
        android:id="@+id/viewstub"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="10dp"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginTop="10dp"
        android:layout="@layout/hide_layout" />
 
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#00ffff"
    android:orientation="vertical" >
    <Button
        android:id="@+id/hide_layout_btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="Click me" />
</LinearLayout>

public class MainActivity extends ActionBarActivity {
	private ViewStub mViewStub;
	private Switch mSwitch;
	private boolean flag = false;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		mViewStub = (ViewStub) this.findViewById(R.id.viewstub);//实例化ViewStub
		mSwitch = (Switch) findViewById(R.id.switch1);
		mSwitch.setOnCheckedChangeListener(new OnCheckedChangeListener() {
			@Override
			public void onCheckedChanged(CompoundButton buttonView,
					boolean isChecked) {
				if (isChecked) {
					if(!flag){
						mViewStub.inflate();//ViewStub只能被inflate一次，会返回一个填充资源的View对象
						//mViewStub.setVisibility(View.VISIBLE);)
						flag = true;
					}else{
						mViewStub.setVisibility(View.VISIBLE);
					}
					Button mBtn = (Button) findViewById(R.id.hide_layout_btn);//ViewStub被替换的布局内的控件
					mBtn.setOnClickListener(new OnClickListener() {
						@Override
						public void onClick(View v) {
							Toast.makeText(getApplicationContext(), "Click me!",
									Toast.LENGTH_SHORT).show();
						}
					});
				} else {
					mViewStub.setVisibility(View.GONE);
				}
			}
		});
	}
}

<merge />标签在UI的结构优化中起着非常重要的作用，它可以删减多余的层级，优化UI。<merge />多用于替换FrameLayout(因为所有的
Activity视图的根结点都是FrameLayout，如果当前的布局根结点是Framelayout，那么可以用merge替代，减少多余的层级)或者当一个布局
包含另一个时，<merge />标签消除视图层次结构中多余的视图组。例如你的主布局文件是垂直布局，又include引入了一个垂直布局，这是
如果include布局使用的LinearLayout就没意义了，使用的话反而减慢你的UI渲染。这时可以使用<merge />标签进行优化。

<merge xmlns:android="http://schemas.android.com/apk/res/android">
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""/>
</merge>