好的，所以我正在关注mybringback的教程，我在哪里设置带位图的背景图片我得到了一个错误，所以我看了一下这里，我使用的代码看到我没有错误，所以我运行应用程序，当我选择一个崩溃的图像 这是我的活动：
package com.odysseus.thebasics;
import java.io.IOException;
import java.io.InputStream;
import android.app.Activity;
import android.app.WallpaperManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
public class TutorialThree extends Activity implements OnClickListener {
MediaPlayer buttonSound;
ImageView display;
int toPhone;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.wallpaper);
final MediaPlayer buttonSound = MediaPlayer.create(TutorialThree.this, R.raw.button_sound);
toPhone = R.drawable.image1;
display = (ImageView) findViewById(R.id.IVdisplay);
ImageView image1 = (ImageView) findViewById(R.id.IVimage1);
ImageView image2 = (ImageView) findViewById(R.id.IVimage2);
ImageView image3 = (ImageView) findViewById(R.id.IVimage3);
ImageView image4 = (ImageView) findViewById(R.id.IVimage4);
Button setWall = (Button) findViewById(R.id.setBackround);
image1.setOnClickListener(this);
image2.setOnClickListener(this);
image3.setOnClickListener(this);
image4.setOnClickListener(this);
setWall.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()){
case R.id.IVimage1:
display.setImageResource(R.drawable.image5);
toPhone = R.drawable.image1;
break;
case R.id.IVimage2:
display.setImageResource(R.drawable.image2);
toPhone = R.drawable.image2;
break;
case R.id.IVimage3:
display.setImageResource(R.drawable.image3);
toPhone = R.drawable.image3;
break;
case R.id.IVimage4:
display.setImageResource(R.drawable.image4);
toPhone = R.drawable.image4;
break;
case R.id.setBackround:
InputStream decode = getResources().openRawResource(toPhone);
Bitmap background = BitmapFactory.decodeStream(decode); //this before was InputStream ....
WallpaperManagermyWallpaperManager=WallpaperManager.getInstance(getApplicationContext()); //error used to be here before i had getApplicationContext().setWallpaper(background);
try{
myWallpaperManager.setBitmap(background);
}catch(IOException e){
e.printStackTrace();
Toast error = Toast.makeText(TutorialThree.this, "Oops, couldn't set image", Toast.LENGTH_LONG);
error.show();
}
break;
}
buttonSound.start();
}
}
这是我的xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ImageView
android:id="@+id/IVdisplay"
android:layout_width="200dp"
android:layout_height="159dp"
android:layout_gravity="center"
android:src="@drawable/image5" />
<Button
android:id="@+id/setBackround"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Set Image To Background" />
<HorizontalScrollView
android:layout_width="200dp"
android:layout_height="200dp"
android:layout_gravity="center" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="25dp"
android:orientation="horizontal" >
<ImageView
android:id="@+id/IVimage1"
android:layout_width="125dp"
android:layout_height="200dp"
android:padding="15dp"
android:src="@drawable/image5" />
<ImageView
android:id="@+id/IVimage2"
android:layout_width="125dp"
android:layout_height="200dp"
android:padding="15dp"
android:src="@drawable/image2" />
<ImageView
android:id="@+id/IVimage3"
android:layout_width="125dp"
android:layout_height="200dp"
android:padding="15dp"
android:src="@drawable/image3" />
<ImageView
android:id="@+id/IVimage4"
android:layout_width="125dp"
android:layout_height="200dp"
android:padding="15dp"
android:src="@drawable/image4" />
</LinearLayout>
</HorizontalScrollView>
</LinearLayout>
我的logcat：
01-09 20:03:03.960: V/MediaPlayer(29999): getDuration
01-09 20:03:03.960: V/MediaPlayer(29999): getCurrentPosition
01-09 20:03:03.970: D/MediaPlayer(29999): start() mUri is null
01-09 20:03:03.980: I/MediaPlayer(29999): mContext.toString() = com.odysseus.thebasics.menu@422c3b50
01-09 20:03:03.980: I/MediaPlayer(29999): setLGSoundNormalizerOnOff(1)
01-09 20:03:03.980: V/MediaPlayer(29999): start
01-09 20:03:04.020: V/MediaPlayer(29999): message received msg=4, ext1=0, ext2=0
01-09 20:03:04.020: V/MediaPlayer(29999): Received seek complete
01-09 20:03:04.020: V/MediaPlayer(29999): All seeks complete - return to regularly scheduled program
01-09 20:03:04.020: V/MediaPlayer(29999): callback application
01-09 20:03:04.020: V/MediaPlayer(29999): back from callback
01-09 20:03:04.040: V/MediaPlayer(29999): getDuration
01-09 20:03:04.040: V/MediaPlayer(29999): getCurrentPosition
01-09 20:03:04.040: V/MediaPlayer(29999): isPlaying: 1
01-09 20:03:04.590: V/MediaPlayer(29999): message received msg=2, ext1=0, ext2=0
01-09 20:03:04.590: V/MediaPlayer(29999): playback complete
01-09 20:03:04.590: V/MediaPlayer(29999): callback application
01-09 20:03:04.590: V/MediaPlayer(29999): back from callback
01-09 20:03:04.590: E/MediaPlayer(29999): ##### MEDIA_PLAYBACK_COMPLETE
01-09 20:03:04.590: V/MediaPlayer(29999): getDuration
01-09 20:03:04.590: V/MediaPlayer(29999): getCurrentPosition
01-09 20:03:04.590: D/MediaPlayer(29999): start() mUri is null
01-09 20:03:06.650: D/dalvikvm(29999): GC_CONCURRENT freed 76K, 5% free 6944K/7303K, paused 20ms+4ms, total 86ms
01-09 20:03:06.650: D/dalvikvm(29999): WAIT_FOR_CONCURRENT_GC blocked 45ms
01-09 20:03:06.750: D/dalvikvm(29999): GC_FOR_ALLOC freed 679K, 14% free 6646K/7687K, paused 23ms, total 23ms
01-09 20:03:06.820: D/dalvikvm(29999): GC_CONCURRENT freed 196K, 10% free 6931K/7687K, paused 21ms+2ms, total 58ms
01-09 20:03:06.820: D/dalvikvm(29999): WAIT_FOR_CONCURRENT_GC blocked 40ms
01-09 20:03:06.820: V/MediaPlayer(29999): constructor
01-09 20:03:06.820: V/MediaPlayer(29999): setListener
01-09 20:03:06.820: V/MediaPlayer(29999): setDataSource(51, 3706, 13890)
01-09 20:03:06.840: V/MediaPlayer(29999): setVideoSurfaceTexture
01-09 20:03:06.840: V/MediaPlayer(29999): prepare
01-09 20:03:06.840: V/MediaPlayer(29999): message received msg=200, ext1=1, ext2=9120
01-09 20:03:06.840: W/MediaPlayer(29999): info/warning (1, 9120)
01-09 20:03:06.840: V/MediaPlayer(29999): callback application
01-09 20:03:06.840: V/MediaPlayer(29999): back from callback
01-09 20:03:06.890: V/MediaPlayer(29999): message received msg=5, ext1=0, ext2=0
01-09 20:03:06.890: V/MediaPlayer(29999): New video size 0 x 0
01-09 20:03:06.890: V/MediaPlayer(29999): callback application
01-09 20:03:06.890: V/MediaPlayer(29999): back from callback
01-09 20:03:06.890: V/MediaPlayer(29999): message received msg=1, ext1=0, ext2=0
01-09 20:03:06.890: V/MediaPlayer(29999): prepared
01-09 20:03:06.890: V/MediaPlayer(29999): signal application thread
01-09 20:03:06.890: V/MediaPlayer(29999): prepare complete - status=0
01-09 20:03:06.900: V/MediaPlayer(29999): callback application
01-09 20:03:06.900: V/MediaPlayer(29999): back from callback
01-09 20:03:06.910: I/MediaPlayer(29999): Info (1,9120)
01-09 20:03:10.300: W/dalvikvm(29999): threadid=1: thread exiting with uncaught exception (group=0x41c2e438)
01-09 20:03:10.330: E/AndroidRuntime(29999): FATAL EXCEPTION: main
01-09 20:03:10.330: E/AndroidRuntime(29999): java.lang.NullPointerException
01-09 20:03:10.330: E/AndroidRuntime(29999): at com.odysseus.thebasics.TutorialThree.onClick(TutorialThree.java:79)
01-09 20:03:10.330: E/AndroidRuntime(29999): at android.view.View.performClick(View.java:4101)
01-09 20:03:10.330: E/AndroidRuntime(29999): at android.view.View$PerformClick.run(View.java:17082)
01-09 20:03:10.330: E/AndroidRuntime(29999): at android.os.Handler.handleCallback(Handler.java:615)
01-09 20:03:10.330: E/AndroidRuntime(29999): at android.os.Handler.dispatchMessage(Handler.java:92)
01-09 20:03:10.330: E/AndroidRuntime(29999): at android.os.Looper.loop(Looper.java:137)
01-09 20:03:10.330: E/AndroidRuntime(29999): at android.app.ActivityThread.main(ActivityThread.java:4940)
01-09 20:03:10.330: E/AndroidRuntime(29999): at java.lang.reflect.Method.invokeNative(Native Method)
01-09 20:03:10.330: E/AndroidRuntime(29999): at java.lang.reflect.Method.invoke(Method.java:511)
01-09 20:03:10.330: E/AndroidRuntime(29999): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798)
01-09 20:03:10.330: E/AndroidRuntime(29999): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565)
01-09 20:03:10.330: E/AndroidRuntime(29999): at dalvik.system.NativeStart.main(Native Method)
你可以自己运行看看我也是android新手所以请理解！提前致谢
答案 0 :(得分：1)
MediaPlayer buttonSound; // already declared but not initialized
ImageView display;
int toPhone;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.wallpaper);
final MediaPlayer buttonSound = MediaPlayer.create(TutorialThree.this, R.raw.button_sound);
// again declared and initialized. local to onCreate.
更改为
buttonSound = MediaPlayer.create(TutorialThree.this, R.raw.button_sound);
此
buttonSound.start();
可能是第79行TutorialThree.java，导致NUllPointerException。