如何将图像添加到画布，以便我可以在其上绘制线条

Question

我有自定义视图的代码，但无法理解如何设置图像，以便我可以在图像上绘制。我已尝试在stackoverflow上给出的解决方案，但图像没有添加任何人可以帮我这个，请检查下面给出的代码：

或者如何将图像设置为我的customview的背景。我只获得白色背景。

public class CustomView extends View {

    private static final String LOG_CAT = CustomView.class.getSimpleName();

    //drawing path
    private Path drawPath;

    //defines what to draw
    private Paint canvasPaint;

    //defines how to draw
    private Paint drawPaint;

    //initial color
    private int paintColor = 0xFF660000;

    private Paint _paintBlur;


    //canvas - holding pen, holds your drawings
    //and transfers them to the view
    private Canvas drawCanvas;

    //canvas bitmap
    private Bitmap canvasBitmap;

    //brush size
    private float currentBrushSize, lastBrushSize;

    private ArrayList<Path> paths = new ArrayList<Path>();
    private ArrayList<Path> undonePaths = new ArrayList<Path>();
    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4;

    private void init(){
        currentBrushSize = 20;
        lastBrushSize = currentBrushSize;

        drawPath = new Path();
        drawPaint = new Paint();
        drawPaint.setColor(paintColor);
        drawPaint.setAntiAlias(true);
        drawPaint.setStrokeWidth(currentBrushSize);
        drawPaint.setStyle(Paint.Style.STROKE);
        drawPaint.setStrokeJoin(Paint.Join.ROUND);
        drawPaint.setStrokeCap(Paint.Cap.ROUND);

        canvasPaint = new Paint(Paint.DITHER_FLAG);

        this._paintBlur = new Paint();
        this._paintBlur.set(drawPaint);
        this._paintBlur.setAntiAlias(true);
        this._paintBlur.setDither(true);
        this._paintBlur.setStyle(Paint.Style.STROKE);
        this._paintBlur.setStrokeJoin(Paint.Join.ROUND);
        this._paintBlur.setStrokeCap(Paint.Cap.ROUND);
        this._paintBlur.setColor(Color.RED);
        this._paintBlur.setStrokeWidth(6);
        this._paintBlur.setMaskFilter(new BlurMaskFilter(10.0F, BlurMaskFilter.Blur.OUTER));

    }


    public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        for (Path p : paths) {
            canvas.drawPath(p, drawPaint);
        }
        canvas.drawPath(drawPath, drawPaint);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
       //create canvas of certain device size.
        super.onSizeChanged(w, h, oldw, oldh);


        //create Bitmap of certain w,h
       canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);

        //apply bitmap to graphic to start drawing.
        drawCanvas = new Canvas(canvasBitmap);

        drawCanvas.drawBitmap(BitmapFactory.decodeResource(getResources(),R.drawable.one),0,0,drawPaint);

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float touchX = event.getX();
        float touchY = event.getY();

        switch (event.getAction()){
            case MotionEvent.ACTION_DOWN:
                touch_start(touchX, touchY);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(touchX, touchY);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
            default:
                return false;
        }
        return true;
    }


    private void touch_start(float x, float y) {
        undonePaths.clear();
        drawPath.reset();
        drawPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void touch_up() {
        drawPath.lineTo(mX, mY);
        drawCanvas.drawPath(drawPath, drawPaint);
        paths.add(drawPath);
        drawPath = new Path();

    }

    private void touch_move(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            drawPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
            mX = x;
            mY = y;
        }
    }


    public void onClickUndo () {
       if (paths.size()>0)
        {
            undonePaths.add(paths.remove(paths.size()-1));
            invalidate();
        }
    }
}

Answer 1

我用错误的方法绘制图像：下面的行必须用onDraw（）方法编写

drawCanvas.drawBitmap(BitmapFactory.decodeResource(getResources(),R.drawable.one),0,0,drawPaint);