如何在cavas中绘制多张位图

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

下面是我的代码：

 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

从您发布的代码中可以看出，函数中的大部分操作都不涉及视图。与视图交互的惟一部分是画布绘制操作。因此，正如注释中所指出的，您应该在工作线程中运行所有计算，然后使用runnable调用runOnUIThread在画布上进行最终绘制。runOnUIThread调用将防止android在修改未绑定到UI的工作线程的视图时抛出错误。

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;
    }
}