java - Android 使 onDraw 无效

Question

我刚刚开始学习android，我在网上搜索了如何强制onDraw更新，我发现的唯一方法是无效的。它可以工作一段时间，但之后就不再更新了。

这是我的代码:

package com.andrewxd.test01;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

public class Game extends View {

    private Bitmap enemy;
    private Paint dpaint;
    private float x,y;

    public Game(Context context) {
        super(context);
        enemy = BitmapFactory.decodeResource(getResources(), R.drawable.enemy);
        enemy = Bitmap.createScaledBitmap(enemy, 300 , 300, false);
        dpaint = new Paint();
        x = 0;
        y = 0;
    }

    @Override
    protected void onDraw(Canvas canvas){
        canvas.drawBitmap(enemy, x, y, dpaint);
        Log.d("GAME", "REDRAWN");
    }

    @Override
    public boolean onTouchEvent(MotionEvent event){
        x = event.getX();
        y = event.getY();
        invalidate();
        return true;
    }
}

有人可以建议我在 x 和 y 更改后重绘的更好方法吗？

Answer 1

来自API-Docs :

The basic cycle of a view is as follows:

• An event comes in and is dispatched to the appropriate view. The view handles the event and notifies any listeners.
• If in the course of processing the event, the view's bounds may need to be changed, the view will call requestLayout().
• Similarly, if in the course of processing the event the view's appearance may need to be changed, the view will call invalidate().
• If either requestLayout() or invalidate() were called, the framework will take care of measuring, laying out, and drawing the tree as appropriate.

所以，这可能是做到这一点的方法!