android drawRect 不绘制任何东西

Question

我遇到了一个问题，这个基本的 drawRect 没有显示任何东西，我不知道为什么。

onDraw

protected void onDraw(Canvas canvas) {
    canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);

    canvas.drawCircle(circle1x, circle1y, circleRadius, circlePaint);
    canvas.drawCircle(circle2x, circle2y, circleRadius, circlePaint);

    canvas.drawRect(rect, rectPaint);
}

---

设置裁剪

在 onDraw 之前运行并从 View 构造函数调用以设置所有 var 的

private void setupCropping() {

    final float scale = getContext().getResources().getDisplayMetrics().density;
    circleRadius = (int) (circleRadiusDp * scale + 0.5f);

    DisplayMetrics metrics = new DisplayMetrics();
    ((Activity) getContext()).getWindowManager().getDefaultDisplay().getMetrics(metrics);
    displayX = metrics.widthPixels;
    displayY = metrics.heightPixels;

    cropAreaY = displayY / 3;
    cropAreaX = displayX;

    //Setting up the circles for adjusting
    circle1x = displayX / 2;
    circle1y = displayY / 2 - (cropAreaY / 2);

    circle2x = displayX / 2;
    circle2y = displayY / 2 + (cropAreaY / 2);

    canvasPaint = new Paint();
    canvasPaint.setColor(0xffffff00);

    circlePaint = new Paint();
    circlePaint.setColor(0xffffff00);
    circlePaint.setAntiAlias(true);

    rectPaint = new Paint();
    rectPaint.setColor(0xffffff00);

    rect = new Rect();
    rect.set(0, circle1y, 0, displayY - cropAreaY - circle1y);

}

drawCircle 完美运行并按照我的预期进行绘制，我已经检查了提供给 drawRect 的数字并且它们已按应有的方式设置，所以我真的不知道这里可能出了什么问题。

全 View 类

package com.samplersnapshoot.domiq.samplersnapshoot;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.concurrent.CountDownLatch;

/**
 * Created by domix on 14.8.2015..
 */
public class CroppingView extends View {

public final String TAG = "DEBUG";

private Canvas cropCanvas;
private Bitmap canvasBitmap;

private int displayX;
private int displayY;

private int circle1x = 0;
private int circle2x = 0;
private int circle1y = 0;
private int circle2y = 0;

private int circleRadiusDp = 20;
private int circleRadius = 100;

private int cropAreaX = 0;
private int cropAreaY = 0;

private Rect rect;

private Paint canvasPaint;
private Paint circlePaint;
private Paint rectPaint;

public CroppingView(Context context, AttributeSet attrs){
    super(context, attrs);
    setupCropping();
}

private void setupCropping() {

    final float scale = getContext().getResources().getDisplayMetrics().density;
    circleRadius = (int) (circleRadiusDp * scale + 0.5f);

    DisplayMetrics metrics = new DisplayMetrics();
    ((Activity) getContext()).getWindowManager().getDefaultDisplay().getMetrics(metrics);
    displayX = metrics.widthPixels;
    displayY = metrics.heightPixels;

    cropAreaY = displayY / 3;
    cropAreaX = displayX;

    //Setting up the circles for adjusting
    circle1x = displayX / 2;
    circle1y = displayY / 2 - (cropAreaY / 2);

    circle2x = displayX / 2;
    circle2y = displayY / 2 + (cropAreaY / 2);

    canvasPaint = new Paint();
    canvasPaint.setColor(0xffffff00);

    circlePaint = new Paint();
    circlePaint.setColor(0xffffff00);
    circlePaint.setAntiAlias(true);

    rectPaint = new Paint();
    rectPaint.setARGB(50, 135, 225, 255);

}

/*@Override
protected void onMeasure (int widthMeasureSpec, int heightMeasureSpec) {
    displayX = widthMeasureSpec;
    displayY = heightMeasureSpec;
    invalidate();
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}*/

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);

    //Getting bitmap
    getPath myPath = new getPath();
    final File myFile = myPath.getLastModifiedFile();

    final CountDownLatch latch = new CountDownLatch(1);
    Thread getCanvasBitmap = new Thread() {
        public void run() {

            BitmapFactory.Options opt = new BitmapFactory.Options();
            opt.inDither = true;
            opt.inPreferredConfig = Bitmap.Config.ARGB_8888;

            int i = 0;
            while (canvasBitmap == null && ++i < 500) {
                System.gc();

                Log.d(TAG, "Trying again: " + i);
                canvasBitmap = BitmapFactory.decodeFile(myFile.getAbsolutePath(), opt);
            }

            latch.countDown();
        }
    };

    getCanvasBitmap.start();
    try {
        latch.await();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    //Turning into mutable bitmap
    myFile.getParentFile().mkdirs();
    RandomAccessFile randomAccessFile = null;
    try {
        randomAccessFile = new RandomAccessFile(myFile, "rw");
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    int bWidth = canvasBitmap.getWidth();
    int bHeight = canvasBitmap.getHeight();
    FileChannel channel = randomAccessFile.getChannel();
    MappedByteBuffer map = null;
    try {
        map = channel.map(FileChannel.MapMode.READ_WRITE, 0, bWidth*bHeight*4);
    } catch (IOException e) {
        e.printStackTrace();
    }
    canvasBitmap.copyPixelsToBuffer(map);
    canvasBitmap.recycle();
    this.canvasBitmap = Bitmap.createBitmap(bWidth, bHeight, Bitmap.Config.ARGB_8888);
    map.position(0);
    this.canvasBitmap.copyPixelsFromBuffer(map);
    try {
        channel.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
    try {
        randomAccessFile.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

protected void onDraw(Canvas canvas) {
    canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);

    Log.d(TAG, "Display vars:" + displayX + " " + displayY);

    canvas.drawCircle(circle1x, circle1y, circleRadius, circlePaint);
    canvas.drawCircle(circle2x, circle2y, circleRadius, circlePaint);

    rect = new Rect();
    rect.set(5, circle1y, displayX, displayY - cropAreaY - circle1y);

    canvas.drawRect(rect, rectPaint);


}
}

这个类的编码还很差，我还没有集成很多功能并清理它。

Answer 1

rect.set(0, circle1y, 0, displayY - cropAreaY - circle1y);

left 和 right 坐标均为 0。看图。

是

rect.set(int left, int top, int right, int bottom);

编辑:

好的，我设法查明了问题所在。以下行在您的 View 类中

rect.set(5, circle1y, displayX, displayY - cropAreaY - circle1y);

在您的代码中使用相同的计算，对于具有 480x800 显示屏的设备，我得到以下坐标值。

rect.set(5, 267, 480, 267);

同样，您的 Rect 有重叠的边； top 和 bottom 两边都在同一个 Y 坐标上。这将生成一个 262 像素宽和零高度的矩形。

您需要做的就是更新您的坐标计算并提供正确的坐标。否则，您的 Rect 应该绘制得很好。