Android矩陣運算拋出IllegalStateException

Question

我定義了一個擴展類View的自定義視圖。

public class MyView extends View{ 
    public MyView(Context context, AttributeSet attrs) { 
    super(context, attrs); 
     Matrix m= new Matrix(); 
     //this line is ok 
     m.setScale(...); 
    } 

    public boolean onTouchEvent(MotionEvent event){ 
     //this same operation throws "IllegalStateException: Matrix can not be modified" 
     m.setScale(...); 
    } 
} 

我想知道爲什麼我得到這樣的例外。我搜索了網頁，但根本沒有發現任何線索。

Answer 1

聲明Matrix對象m在如下一流水平...

public class MyView extends View{ 

    Matrix m; 

    public MyView(Context context, AttributeSet attrs) { 
     super(context, attrs); 

     m = new Matrix(); 
     m.setScale(...); 
    } 

    public boolean onTouchEvent(MotionEvent event){ 

     m.setScale(...); 

     return true; 
    } 
}