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我有一些問題,在我的代碼中我想繪製frameLayout畫布,但我得到空對象引用異常。順便說一下,當我改變Color.BLACK沒有改變只顯示黑色的矩形,並給出錯誤。 我使用Android 2.1的工作室和genymotion Android模擬器6.0棉花糖Android繪圖顏色空指針異常
錯誤是這樣的:
Fatal Exception:main
Process:com.example.myApp
java.lang.NullPointerException : Attempt to invoke virtual method "void android.graphics.Canvas.rawColor(int)" on a null object reference
public class MyCanvas extends SurfaceView implements SurfaceHolder.Callback{
private boolean mRun= false;
private final SurfaceHolder mSurfaceHolder;
private final Object mRunLock = new Object();
public MyCanvas(Context context, AttributeSet attrs){
super(context,attrs);
this.setWillNotDraw(false);
mSurfaceHolder = getHolder();
mSurfaceHolder.AddCallback(this);
}
public synchronized void run(){
if(mRun){
Canvas c = null;
try{
c = mSurfaceHolder.lockCanvas();
synchronized (mSurfaceHolder){
synchronized(mRunLock){
if(mRun) doDraw(c);
}
}
}finally
if(c != null)
{ mSurfaceHolder.unlockCanvasandPost(c); }
}
}
private void onDraw(Canvas canvas){
canvas.drawColor(Color.YELLOW);
}
}
我的活動佈局代碼是在這裏。
<view class="com.example.myapp.MyCanvas"
android:layout_width="200dp"
android:layout_height="200dp"
android:lid="@+id/mycanvas"
/>
我的活動課就在這裏
MyCanvas myCanvas = (MyCanvas)findViewById(R.id.mycanvas);
myCanvas.run();
謝謝surfacedestroyed方法的工作。當我將mRun分配給false時,錯誤消失了。 –