Android Canvas to Bitmap

Question

我一直在网上搜索如何将画布上的内容转换为位图。我尝试过多种方法，比如将绘图缓存保存为位图，但最终的结果是背景位图闪烁了片刻，然后变成了黑屏。测试图像显示在背景上，但不会因为下一次调用OnDraw而被背景覆盖。

MainThreading{

                        ...

              if(notuptodate == true){

                        //call readyBackground to create the background bitmap
                        this.mainPanel.readyBackground(canvas);
                        //post the canvas
                        surfaceHolder.unlockCanvasAndPost(canvas);
                        //clean the Canvas
                        canvas = null;
                        //ready new Canvas
                        canvas = this.surfaceHolder.lockCanvas();//lock the canvas to enable editing






                    }//if not true

                    if (MainThreading.notuptodate == false){

                        mainPanel.onDraw(canvas);


                    }//if false
...
                 }//mainthreading

    //this method is run first to create the Bitmap that on draw will use
    public void readyBackGround(Canvas canvas){


        if (MainThreading.notuptodate){
            //method used to draw multiple Bitmaps onto the canvas
            renderBackground(canvas);

            //private Bitmap, this is the supposed proper size of the bitmap
            backgroundBitmap=Bitmap.createBitmap(240, 320, Config.ARGB_8888);


            //set the canvas to turn whats on its self onto the bitmap.
            canvas.setBitmap(backgroundBitmap);

            //set boolean flag to false so renderBackground won't be called
            //untill it needs to be updated again
            MainThreading.notUpToDate = false;

        }

        //this method is called when notUpToDate = true
         @Override
    protected void onDraw(Canvas canvas){


        if (this.threado.getBackground() != null){
            canvas.drawBitmap(backgroundBitmap, 0, 0, null);

            }

            //this if statement is never activated
            if (this.threado.getBackground() == null){
                Log.d("background nonexistant", "Importante!");
            }
            //draw test object onto background
            test.DrawObject(canvas);

                //when MainThreading.notUpToDate = true isn't commented out, the
                //screen consistantly shows the background, but the test object isn't
                //drawn

        //MainThreading.notUpToDate = true;





        }

Answer 1

试着这样..。

-使用Bitmap.createBitmap()创建大小正确的bitmap

-使用Canvas(Bitmap)构造函数创建指向此位图的canvas instance

-绘制到canvas

-使用bitmap

Answer 2

public class CanvasToBitmap extends View {

    Paint paint = new Paint();
    Rect mRect = new Rect();
    Bitmap bitmap = Bitmap.createBitmap(200, 200, Bitmap.Config.ARGB_8888);

    public myCanvas( Context context ) {
        super(context);
        Canvas canvas = new Canvas(bitmap);
        draw(canvas);
    }

    @Override
    public void onDraw(Canvas canvas) {
        
        mRect.set(0, 0, 200, 200);
        paint.setColor(Color.GREEN);
        paint.setStyle(Paint.Style.FILL);
        canvas.drawRect(mRect, paint);
        canvas.setBitmap(bitmap);

        ByteArrayOutputStream mByteArrayOutputStream = new ByteArrayOutputStream();
        try{
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, mByteArrayOutputStream);

            bitmap = BitmapFactory.decodeStream(new ByteArrayInputStream(mByteArrayOutputStream.toByteArray()));
            mByteArrayOutputStream.close();
       } catch (Exception e) {e.printStackTrace();}
    }
}

创建一个新实例：

CanvasToBitmap canvasToBitmap = new CanvasToBitmap(getBaseContext());

获取canvasToBitmap的位图：

Bitmap bitmap = canvasToBitmap.bitmap;