Android LayerDrawable

Android LayerDrawable可以将两个甚至多个图片合成一个Drawable。如下面截图，第三个图片就是第一个图片和第二个图片合成的，当然这只是一个简单的例子，不同场景怎么用还得看自己需要。

实现如下：
新建activity_main.xml

<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.test.layerdrawable.MainActivity" >

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/actionbar_send_icon_press" 
        android:layout_marginBottom="10dp"/>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/chat_bottom_send_normal" 
        android:layout_marginBottom="10dp"/>

    <ImageView
        android:id="@+id/iv_layerdrawable"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

新建MainActicity.java

package com.test.layerdrawable;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.LayerDrawable;
import android.os.Bundle;
import android.widget.ImageView;

public class MainActivity extends Activity {
    ImageView iv_layerdrawable;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }
    @SuppressLint("NewApi")
    private void initView() {
        iv_layerdrawable = (ImageView) findViewById(R.id.iv_layerdrawable);
        Drawable drawable1 = getResources().getDrawable(R.drawable.chat_bottom_send_normal);
        Drawable drawable2 = getResources().getDrawable(R.drawable.actionbar_send_icon_press);
        LayerDrawable layerDrawable = new LayerDrawable(new Drawable[]{drawable1,drawable2});
        iv_layerdrawable.setBackground(layerDrawable);
    }

}

至此，两个图片叠加已经实现.