android - onDraw 在创建时不触发

Question

我的自定义 View 的 onDraw() 没有被触发。为什么？我正在使用 2.3.3。 View 创建时不应该自动绘制吗？ onMeasure() 方法被触发，我得到正确的屏幕宽度和高度。

package com.example.assignment2b;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.Log;
import android.view.Display;
import android.view.Menu;
import android.view.View;
import android.view.WindowManager;

public class AcesActivity extends Activity {

    private static final String TAG = "DEBUG";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        HeartView heartView = new HeartView(this);
        setContentView(heartView);
        heartView.invalidate();
    }


    class HeartView extends View {

        private int screenWidth;
        private int screenHeight;
        private Context context;

        public HeartView(Context context) {
            super(context);
            this.context = context;

        }

        @Override
        public void onDraw(Canvas canvas)  {
            Log.println(Log.DEBUG, TAG, "onDraw fired"); 
            int cardWidth = screenWidth - 10;
            int cardHeight = (int) (cardWidth * 1.4);


            canvas.drawColor(Color.DKGRAY);

            Paint paint = new Paint();
            paint.setColor(Color.WHITE);
            paint.setStyle(Paint.Style.FILL);
            canvas.drawRect(5, (screenHeight/2) - (cardHeight/2), screenWidth - 5, (screenHeight/2) + (cardHeight/2), paint);
            paint.setColor(Color.BLACK);
            paint.setStyle(Paint.Style.STROKE);
            canvas.drawRect(5, (screenHeight/2) - (cardHeight/2), screenWidth - 5, (screenHeight/2) + (cardHeight/2), paint);

        }

        @Override
        public void onMeasure(int width, int height) {
            Log.println(Log.DEBUG, TAG, "onMeasure fired"); 
            WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
            Display display = wm.getDefaultDisplay(); 
            screenWidth = display.getWidth();
            screenHeight = display.getHeight();
            setMeasuredDimension(screenWidth, screenHeight);
            Log.println(Log.DEBUG, TAG, "screenWidth = " + screenWidth); 
            Log.println(Log.DEBUG, TAG, "scrrenHeight = " + screenHeight); 
            super.onMeasure(screenWidth, screenHeight);
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        return true;
    }
}

Answer 1

一些不同的问题正在发生。首先正如@dragonwrenn 所建议的那样，如果没有 ViewGroup 和布局参数，您的 View 就没有内在边界。调用 invalidate() 是不必要的，但不会有问题。

public class AcesActivity extends Activity {

    private static final String TAG = "DEBUG";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        RelativeLayout rl = new RelativeLayout(this);
        RelativeLayout.LayoutParams params = new 
            RelativeLayout.LayoutParams(LayoutParams.MATCH_PARENT,
            LayoutParams.MATCH_PARENT);
        setContentView(rl);

        HeartView heartView = new HeartView(this);
        heartView.setLayoutParams(params);
        rl.addView(heartView);    
    }

    class HeartView extends View {

        private int screenWidth;
        private int screenHeight;
        private Context context;

         // Moved a couple of variable declarations out of the onDraw method
        Paint paint;
        int cardWidth;
        int cardHeight;

        public HeartView(Context context) {
            super(context);
            this.context = context;
            paint = new Paint();

        }

其次，您对矩形的数学运算使它们超出了屏幕的边界。我输入了一些硬性数字作为测试。你会想要重新处理你的数字以获得你真正想要的。另外，你的笔划没有宽度，所以请注意

        @Override
        public void onDraw(Canvas canvas)  {

            Log.println(Log.DEBUG, TAG, "onDraw fired"); 

            canvas.drawColor(Color.DKGRAY);

            paint.setColor(Color.WHITE);
            paint.setStyle(Paint.Style.FILL);
            canvas.drawRect(10, 10, 50, 50, paint);
            paint.setColor(Color.BLACK);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeWidth(3);
            canvas.drawRect(10, 10, 50, 50, paint);

        }

第三，我不确定 onMeasure 中的所有内容都试图实现什么，但它会导致 View 出现问题。你不应该需要比下面更多的东西:

        @Override
        public void onMeasure(int width, int height) {
            Log.println(Log.DEBUG, TAG, "onMeasure fired"); 
            screenWidth = width;
            screenHeight = height;

            Log.println(Log.DEBUG, TAG, "screenWidth = " + screenWidth); 
            Log.println(Log.DEBUG, TAG, "scrrenHeight = " + screenHeight); 
            super.onMeasure(screenWidth, screenHeight);
            cardWidth = screenWidth - 10;
            cardHeight = (int) (cardWidth * 1.4);
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        return true;
    }
}

编辑:请注意，以上是在 Eclipse 中测试的功能代码。如果每个部分都被准确地复制和粘贴，它将起作用。