Transition对应的标签是<transition>,，他用于显示两个Drawable之间的淡入淡出的效果。

<?xml version="1.0" encoding="utf-8"?>
<transition
xmlns:android="http://schemas.android.com/apk/res/android" >
        android:drawable="@[package:]drawable/drawable_resource"
        android:id="@[+][package:]id/resource_name"
        android:top="dimension"
        android:right="dimension"
        android:bottom="dimension"
        android:left="dimension" />
</transition>
上面的子节点都比较简单，下面我们直接看代码效果吧
transition_simple.xml
<?xml version="1.0" encoding="utf-8"?>
<transition xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@mipmap/pic1" />
    <item android:drawable="@mipmap/pic2" />
</transition>
import android.app.Activity;
import android.graphics.drawable.TransitionDrawable;
import android.os.Bundle;
import android.widget.ImageView;
public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ImageView image = (ImageView) findViewById(R.id.mIv);
        //得到一个Drawable，属于 TransitionDrawable 类型的
        TransitionDrawable transition = (TransitionDrawable)getResources().
                getDrawable(R.drawable.transition_simple);
        image.setImageDrawable(transition);
        transition.startTransition(2000); // 设定渐变的变化市场