在Draw方法中位圖的NullPointer

我正試圖在畫布上繪製位圖。位圖返回null，但我不明白爲什麼。我已經閱讀了Bitmap和decodeResources的文檔。它看起來像drawable返回null，因爲解碼無法找到它。我試圖使用調試會話，但我不是很遠。在Draw方法中位圖的NullPointer

請指出空例外。

故障類別：

public class SnapShot extends Activity { 

private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG); 

public void draw(Canvas canvas) { 
    drawIcon(canvas);  
} 

private void drawIcon(Canvas canvas) { 
    Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.buttongreen); //this is line 36 
    canvas.drawBitmap(bitmap, 150, 150, paint); 
}

}

堆棧跟蹤：

10-01 09:24:30.638: E/AndroidRuntime(27206): FATAL EXCEPTION: main 
10-01 09:24:30.638: E/AndroidRuntime(27206): java.lang.NullPointerException 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.content.ContextWrapper.getResources(ContextWrapper.java:80) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at com.game.SnapShot.drawIcon(SnapShot.java:36) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at com.game.SnapShot.draw(SnapShot.java:29) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at com.game.onDraw(AugmentedView.java:77) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.View.draw(View.java:6880) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.ViewGroup.drawChild(ViewGroup.java:1646) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.View.draw(View.java:6883) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.widget.FrameLayout.draw(FrameLayout.java:357) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.ViewGroup.drawChild(ViewGroup.java:1646) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.View.draw(View.java:6883) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.widget.FrameLayout.draw(FrameLayout.java:357) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1862) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.ViewRoot.draw(ViewRoot.java:1522) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.ViewRoot.performTraversals(ViewRoot.java:1258) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.view.ViewRoot.handleMessage(ViewRoot.java:1859) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.os.Handler.dispatchMessage(Handler.java:99) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.os.Looper.loop(Looper.java:130) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at android.app.ActivityThread.main(ActivityThread.java:3683) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at java.lang.reflect.Method.invokeNative(Native Method) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at java.lang.reflect.Method.invoke(Method.java:507) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
10-01 09:24:30.638: E/AndroidRuntime(27206): at dalvik.system.NativeStart.main(Native Method)

來源

2012-10-01 KDEx

需要更多信息，也許設定線36斷點，看空的對象是什麼。 – iCantSeeSharp

@Souvlaki使用調試器告訴我ViewRoot.draw（boolean）返回null。從閱讀decodeResource如何工作如果無法找到位圖的int ID它將返回null。然而使用R.drawable格式應該返回id的權利？它編譯，所以我會假設它可以在該方法中找到可繪製的罰款.. – KDEx

如果你寫的drawIcon（帆布油畫）方法的視圖裏面，那麼你應該有一個上下文調用getResource（）。

如：

Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.buttongreen); 
    canvas.drawBitmap(bitmap, 150, 150, paint);

來源

2012-10-01 13:49:19 Androider

非常好，謝謝。對於其他人，我不得不從實際活動傳遞上下文，因爲這個類是覆蓋..所以嘗試「繪製（畫布畫布，上下文上下文）」，它將工作 – KDEx

在Draw方法中位圖的NullPointer

回答

相關問題