如何在画布上绘制许多位图

Question

我想在画布上绘制许多位图，但 android 显示：“应用程序可能在其主线程上做了太多工作”并且应用程序无法运行。 [ cloud_number 超过 50 ]

这是我的代码：

 fun draw_beautiful(canvas: Canvas){

    val mPaint: Paint = Paint()
    mPaint.style = Paint.Style.FILL
    mPaint.isAntiAlias = true
    mPaint.color= Color.BLACK

    var vt = 0; var x1 =0f; var y1 =0f;var style =0;

    for (i in 1..cloud_number){
        vt = i*4-3
        style = mt_cloud[vt]
        x1  = mt_cloud[vt+2].toFloat()
        y1 = mt_cloud[vt+3].toFloat()

        
        var ob= canvas_cloud1
        if (style==0) ob= canvas_cloud1
        else if (style==1) ob= canvas_cloud2
        else if (style==2) ob= canvas_cloud3

        canvas.drawBitmap(ob, x1,y1 , mPaint)

    }

}

Answer 1

从您发布的代码来看，函数中的大部分操作不涉及视图。唯一与视图交互的部分是画布绘制操作。因此，正如 cmets 中所指出的，您应该在工作线程中运行所有计算，然后调用带有可运行对象的 runOnUIThread 以在画布上进行最终绘图。当您从未绑定到 UI 的工作线程修改视图时，runOnUIThread 调用将防止 android 引发错误。

这里的选项显然是 AsyncTask 和线程类。在下面的示例中，我使用的是 AyncTask。

void draw_beautiful(Canvas canvas) {
        MyDrawingWorkerTask myDrawingWorkerTask = new MyDrawingWorkerTask(this);
        myDrawingWorkerTask.execute(canvas);
    }


/**
 * A class for doing a lot of the work in a background
 */
private static class MyDrawingWorkerTask extends AsyncTask<Canvas, Void, Void> {

    private final Activity activity;

    public MyDrawingWorkerTask(Activity activity) {// add more parameters to use to set other variables like cloud_number, etc
        this.activity = activity;
    }

    // This is where the work is being done
    @Override
    protected Void doInBackground(Canvas... canvases) {
        final Canvas canvas = canvases[0];
        final Paint mPaint = new Paint();
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setAntiAlias(true);
        mPaint.setColor(Color.BLACK);

        int vt = 0;
        float x1 = 0f;
        float y1 = 0f;
        int style = 0;

        for (int i = 0; i < cloud_number; i++) {
            vt = i * 4 - 3;
            style = mt_cloud[vt];
            x1 = mt_cloud[vt + 2].toFloat();
            y1 = mt_cloud[vt + 3].toFloat();


            Bitmap ob = canvas_cloud1;
            if (style == 0) ob = canvas_cloud1;
            else if (style == 1) ob = canvas_cloud2;
            else if (style == 2) ob = canvas_cloud3;

            Bitmap finalOb = ob;
            float finalX = x1;
            float finalY = y1;

            // note that this is what interacts with the view
            activity.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    canvas.drawBitmap(finalOb, finalX, finalY, mPaint);
                }
            });
        }
        return null;
    }
}