我得到一个NullPointerException异常和故障使用相机

Question

我已经看过了很多其他的问题就到这里之后，从onActivityResult交付结果异常在我的Android应用程序，但没有似乎是我的帮助。我正在写作和应用程序，你按下按钮打开相机。这工作正常，但只要我去保存图片崩溃，我得到的错误。 这里是我的代码迄今

public class MainActivity extends Activity { 

    private int TAKE_PICTURE = 1337; 
    private Uri outputFileUri; 
    private int screenHeight; 
    private int screenWidth; 
    private ImageView background; 
    private String ORIGINAL_FILE = "photo.jpg"; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     Button take = (Button)findViewById(R.id.take); 
     Button share = (Button)findViewById(R.id.share); 
     take.setOnClickListener(new takeInstr(this)); 
     ImageView background = (ImageView)findViewById(R.id.background); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.activity_main, menu); 
     return true; 
    } 


    public void startCamera() { 
     Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); 
     File file = new File(Environment.getExternalStorageDirectory(), ORIGINAL_FILE); 
     outputFileUri = Uri.fromFile(file); 
     intent.putExtra(MediaStore.EXTRA_OUTPUT, outputFileUri); 
     startActivityForResult(intent, TAKE_PICTURE); 
    } 
    @Override 
    protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
     if (requestCode == TAKE_PICTURE && resultCode != RESULT_CANCELED) { 
      if (data != null) { 
       BitmapFactory.Options options = new BitmapFactory.Options(); 
       options.inJustDecodeBounds = true; 
       String file = Environment.getExternalStorageDirectory() + "/test.jpg"; 
       BitmapFactory.decodeFile(file, options); 
       int imageHeight = options.outHeight; 
       int imageWidth = options.outWidth; 
       String imageType = options.outMimeType; 
       DisplayMetrics metrics = this.getResources().getDisplayMetrics(); 
       screenHeight = metrics.heightPixels; 
       screenWidth = metrics.widthPixels; 
       int heightRatio = Math.round((float) imageHeight/(float) screenHeight); 
       int widthRatio = Math.round((float) imageWidth/(float) screenWidth); 
       options.inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio; 
       options.inJustDecodeBounds = false; 
       background.setImageBitmap(BitmapFactory.decodeFile(file, options)); 
      } 
      else { 


      } 
     } 
    } 
} 

package com.example.photoshare; 



import android.view.View; 
import android.view.View.OnClickListener; 

public class takeInstr implements OnClickListener { 
    private MainActivity mainActivity; 
    public takeInstr(MainActivity mainActivity) { 
     this.mainActivity = mainActivity; 
    } 
    @Override 
    public void onClick(View v) { 
     mainActivity.startCamera(); 

    } 

} 

`

我的XML

<RelativeLayout 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" 
tools:context=".MainActivity" > 

<ImageView 
    android:id="@+id/background" 
    android:src="@drawable/great_wall" 
    android:layout_width="fill_parent" 
    android:scaleType="fitXY" 
    android:layout_height="fill_parent" /> 

<LinearLayout 
    android:id="@+id/buttonLayout" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:layout_alignParentBottom="true" 
    android:layout_alignParentLeft="true" 
    android:gravity="center_horizontal" 
    android:weightSum="1.0" > 

    <Button 
     android:id="@+id/take" 
     android:layout_width="0dip" 
     android:layout_height="wrap_content" 
     android:layout_weight="0.5" 
     android:text="@string/take" /> 

    <Button 
     android:id="@+id/share" 
     android:layout_width="0dip" 
     android:layout_height="wrap_content" 
     android:layout_weight="0.5" 
     android:text="@string/share" /> 
</LinearLayout> 

，这里是我的logcat消息

02-18 12:42:56.266: W/dalvikvm(627): threadid=1: thread exiting with uncaught exception (group=0x409c01f8) 
02-18 12:42:56.357: E/AndroidRuntime(627): FATAL EXCEPTION: main 
02-18 12:42:56.357: E/AndroidRuntime(627): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1337, result=-1, data=null} to activity {com.example.photoshare/com.example.photoshare.MainActivity}: java.lang.NullPointerException 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.app.ActivityThread.deliverResults(ActivityThread.java:2980) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.app.ActivityThread.handleSendResult(ActivityThread.java:3023) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.app.ActivityThread.access$1100(ActivityThread.java:123) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1177) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.os.Handler.dispatchMessage(Handler.java:99) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.os.Looper.loop(Looper.java:137) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.app.ActivityThread.main(ActivityThread.java:4424) 
02-18 12:42:56.357: E/AndroidRuntime(627): at java.lang.reflect.Method.invokeNative(Native Method) 
02-18 12:42:56.357: E/AndroidRuntime(627): at java.lang.reflect.Method.invoke(Method.java:511) 
02-18 12:42:56.357: E/AndroidRuntime(627): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
02-18 12:42:56.357: E/AndroidRuntime(627): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
02-18 12:42:56.357: E/AndroidRuntime(627): at dalvik.system.NativeStart.main(Native Method) 
02-18 12:42:56.357: E/AndroidRuntime(627): Caused by: java.lang.NullPointerException 
02-18 12:42:56.357: E/AndroidRuntime(627): at com.example.photoshare.MainActivity.onActivityResult(MainActivity.java:69) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.app.Activity.dispatchActivityResult(Activity.java:4649) 
02-18 12:42:56.357: E/AndroidRuntime(627): at android.app.ActivityThread.deliverResults(ActivityThread.java:2976) 
02-18 12:42:56.357: E/AndroidRuntime(627): ... 11 more 
02-18 12:42:56.686: I/dalvikvm(627): threadid=3: reacting to signal 3 
02-18 12:42:56.726: I/dalvikvm(627): Wrote stack traces to '/data/anr/traces.txt' 
02-18 12:42:57.047: I/dalvikvm(627): threadid=3: reacting to signal 3 
02-18 12:42:57.086: I/dalvikvm(627): Wrote stack traces to '/data/anr/traces.txt' 
02-18 12:42:59.716: I/Process(627): Sending signal. PID: 627 SIG: 9 

我知道我应该做一些什么时候它返回null，但我不知道该怎么做，所有的帮助将不胜感激。

Answer 1

有在你的代码两个不同的东西，可能是零。第一个可能是BitmapFactory无法解码您提供的文件的问题。你也确定你只想解码test.jpg而不是相机拍摄的那个？

第二个可能是您的background视图的问题。基于发射类型的活动，它是might happen是onActivityResult()之前onCreate()称为这将导致background变量仍然为空。

为了深入挖掘，应先分配解码位图到一个新的变量，看看它是否为空或不是，并检查background是空...