Question

我无法理解为什么第一次在自定义视图中调用this.invalidate时，方法onDraw()被调用两次（对相同变量执行双重操作）。之后，每次用户按下按钮时，onDraw()都会被调用一次。这是代码：

MyActivity

MyView mCustomView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_interval_identification);

    mCustomView = (MyView) findViewById(R.id.my_view);
    Button mButton = (Button) findViewById(R.id.id_btn);

    mButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            newDrawing();
        }
    });

    newDrawing();

}

private void newDrawing() {

    int a;
    int b;

    //some operations on 'a' and 'b'

    mCustomView.newDrawing(a, b);

}

MyView的

int x;
int y;

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Drawable object = ContextCompat.getDrawable(getContext(), R.drawable.object);

    //some operations

    object.draw(canvas); //based on 'x' and 'y'
}

public void newDrawing(int a, int b) {
    x = a;
    y = b;
    this.invalidate();
}

Answer 1

尝试在newDrawing();的{{1}}方法中对newDrawing(); --> //newDrawing();（onCreate）发表评论。似乎系统首次自动调用MyActivity。

'onDraw（）'在第一次调用'invalidate'时调用两次

1 个答案: