invalidate() doesn't recall OnDraw method

问题:

invalidate() doesn't recall my OnDraw() method. I use invalidate() in a setter method in the same class that OnDraw() is in.

public class PuzzleDraw extends View {

    // defining some variables //

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // codes for painting puzzle //
    }

    public PuzzleDraw(Context context) {
        super(context);
    }

    // Method for giving cursor X/Y from MainActivity OnTouch() method and using it in OnDraw() method in some part of painting code //

    public void setCursor(int i, int j) {
        this.xx = i;
        this.yy = j;
        invalidate();
    } 

When I debug my code, everything is good except RECALLING OnDraw() when invalidate() executes... in fact, invalidate() is doing nothing for me! What is wrong? I used postInvalidate(), this.invalidate(), this.postInvalidate() too, but nothing changed.

回答1:

Calling to invalidate() wouldn't execute onDraw directly, it only sets the appropriate flag in the View class. Your onDraw method will be called by framework the next time when view hierarchy is traversed.

回答2:

You might be calling setCursor(float, float) method only a single time by calling it from activity but invalidate method have to be called again and again if you wish to call onDraw method internally by the framework itself.

Hope this will work