<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/linearLayout1"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical"    android:padding="10dp" >    <TextView        android:id="@+id/textView1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="改变图片透明度"        android:textAppearance="?android:attr/textAppearanceLarge" />    <!--         android:numStars 多少颗星        android:rating 默认多少颗星        android:stepSize 最小变动0.5颗星     -->    <RatingBar        android:id="@+id/ratingBar1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:numStars="4"        android:rating="4"        android:stepSize="0.5"         />    <ImageView        android:id="@+id/imageView1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:src="@drawable/pic1" /></LinearLayout>

public class MainActivity extends Activity{    RatingBar ratingBar1;    ImageView imageView1;        Handler handler=new Handler(){        public void handleMessage(Message msg) {            if(msg.what==123){                float alpha =msg.getData().getFloat("alpha");                imageView1.setImageAlpha((int)alpha);            }        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                imageView1=(ImageView)findViewById(R.id.imageView1);        ratingBar1=(RatingBar)findViewById(R.id.ratingBar1);        ratingBar1.setOnRatingBarChangeListener(new OnRatingBarChangeListener() {                        @Override            public void onRatingChanged(RatingBar ratingBar, float rating,                    boolean fromUser) {                Message msg=new Message();                msg.what=123;                Bundle data=new Bundle();                //rating:当前是几颗星                //getNumStars:总共多少颗星                //rating*255/ratingBar1.getNumStars():在255中的位置                data.putFloat("alpha", rating*255/ratingBar1.getNumStars());                msg.setData(data);                handler.sendMessage(msg);                            }        });            }}