<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">    <ImageView        android:id="@+id/image"        android:layout_width="wrap_content"        android:layout_height="240sp"        android:src="@drawable/lijiang" />        <SeekBar        android:id="@+id/seekBar"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_marginBottom="57dp"         android:max="255"        android:progress="255"        android:thumb="@drawable/ic_launcher"/></LinearLayout>

package com.example.seekbar;import android.app.Activity;import android.os.Bundle;import android.widget.ImageView;import android.widget.SeekBar;import android.widget.SeekBar.OnSeekBarChangeListener;public class MainActivity extends Activity {    ImageView image;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        image=(ImageView) findViewById(R.id.image);        SeekBar seekBar=(SeekBar) findViewById(R.id.seekBar);        seekBar.setOnSeekBarChangeListener(new OnSeekBarChangeListener(){            @Override            public void onProgressChanged(SeekBar seekBar, int progress,                    boolean fromUser) {                image.setImageAlpha(progress);            }            @Override            public void onStartTrackingTouch(SeekBar seekBar) {            }            @Override            public void onStopTrackingTouch(SeekBar seekBar) {            }                    });    }}