與Android的麻煩

Question

我在繪製ImageView時有一個。當從onCreate（）繪製一切OK時，但是當我通過按下按鈕（函數「qwe」）繪製出錯時。哪裏不對？

package com.example.asd; 

    import android.app.Activity; 
    import android.graphics.Bitmap; 
    import android.graphics.Canvas; 
    import android.graphics.Paint; 
    import android.os.Bundle; 
    import android.view.View; 
    import android.widget.ImageView; 

    public class MainActivity extends Activity { 
     Bitmap myBitmap; 
     Canvas myCanvas; 
     ImageView myImageView; 
     @Override 
     protected void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.activity_main); 
      config(); 
     } 
     public void config() 
     { 
      myBitmap=Bitmap.createBitmap(500, 500, Bitmap.Config.ARGB_8888); 
       myCanvas=new Canvas(myBitmap); 
       myImageView =(ImageView)findViewById(R.id.imageView1); 
      for(int i=0;i<200;i++) 
       for(int j=0;j<200;j++) 
        myBitmap.setPixel(i, j, 0xffffff00); 
      myImageView.setImageBitmap(myBitmap); 
      Paint myPaint=new Paint(); 
      myPaint.setColor(0xff000000); 
      myCanvas.drawLine(10, 10, 190, 190, myPaint); 
     } 
     public void qwe(View v) 
     { Paint myPaint=null; 
      myPaint.setColor(0xff000000); 
      myCanvas.drawLine(190, 10, 190, 10, myPaint); 
      myImageView.draw(myCanvas); 
     } 
    } 

Answer 1

你這裏得到NullPointerException：

Paint myPaint=null; 
     myPaint.setColor(0xff000000); 

您在使用它之前啓動myPaint！

Paint myPaint= new Paint();