<?xml version="1.0" encoding="utf-8"?>
<com.storm.fliplayout.lib.FlipLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/flipLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:layout_gravity="center"
        android:background="#FFCCCCCC"
        android:gravity="center"
        android:text="@string/front"
        android:textAppearance="@android:style/TextAppearance.Large" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:layout_centerInParent="true"
        android:layout_gravity="center"
        android:background="#FF999999"
        android:gravity="center"
        android:text="@string/back"
        android:textAppearance="@android:style/TextAppearance.Large"
        android:visibility="gone" />

</com.storm.fliplayout.lib.FlipLayout>

<android.support.v4.widget.SwipeRefreshLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/swipe_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
 
        <TextView
            android:text="@string/hello_world"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="16dp"
            android:gravity="center"/>
    </ScrollView>
 
</android.support.v4.widget.SwipeRefreshLayout>

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
 
    swipeLayout = (SwipeRefreshLayout) findViewById(R.id.swipe_container);
    swipeLayout.setOnRefreshListener(this);
    swipeLayout.setColorScheme(android.R.color.holo_blue_bright, 
            android.R.color.holo_green_light, 
            android.R.color.holo_orange_light, 
            android.R.color.holo_red_light);
}
 
public void onRefresh() {
    new Handler().postDelayed(new Runnable() {
        @Override public void run() {
            swipeLayout.setRefreshing(false);
        }
    }, 5000);
}

view.setAlpha(0.5f);
View.ALPHA.set(view, 0.5f);
ObjectAnimator.ofFloat(view, "alpha", 0.5f).start();
view.animate().alpha(0.5f).start();
view.setAnimation(new AlphaAnimation(1.0f, 0.5f));

canvas.saveLayer(l, r, t, b, 127, Canvas.CLIP_TO_LAYER_SAVE_FLAG);

// Not this
textView.setAlpha(alpha);

// 以下方式可以避免创建 offscreen buffer
int newTextColor = (int) (0xFF * alpha) << 24 | baseTextColor & 0xFFFFFF;
textView.setTextColor(newTextColor);

// Not this, setAlpha方法由View继承而来，性能不佳
imageView.setAlpha(0.5f);

// 使用以下方式时，ImageView会在绘制图片时单独为图片指定Alpha
// 可以避免创建 offScreenBuffer
imageView.setImageAlpha((int) alpha * 255);

// Not this
customView.setAlpha(alpha);

// But this
paint.setAlpha((int) alpha * 255);
canvas.draw*(..., paint);

/**
 * Returns whether this View has content which overlaps. This function, intended to be
 * overridden by specific View types, is an optimization when alpha is set on a view. If
 * rendering overlaps in a view with alpha < 1, that view is drawn to an offscreen buffer
 * and then composited it into place, which can be expensive. If the view has no overlapping
 * rendering, the view can draw each primitive with the appropriate alpha value directly.
 * An example of overlapping rendering is a TextView with a background image, such as a
 * Button. An example of non-overlapping rendering is a TextView with no background, or
 * an ImageView with only the foreground image. The default implementation returns true;
 * subclasses should override if they have cases which can be optimized.
 *
 * @return true if the content in this view might overlap, false otherwise.
 */
public boolean hasOverlappingRendering() {
    return true;
}