清除画布并在其中再次绘制答案

【问题标题】：Clear canvas and draw again inside it清除画布并在其中再次绘制
【发布时间】：2019-07-27 19:36:09
【问题描述】：

我正在尝试在我的应用程序中创建一个“全部清除”按钮，但它不起作用。这是我用来创建和使用画布的代码：

public DrawingView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setLayerType(LAYER_TYPE_HARDWARE, null);
        startActivity = System.currentTimeMillis();
        setupDrawing();
    }

    public void setDimension (DisplayMetrics displaymetrics) {
        height = displaymetrics.heightPixels;
        width = displaymetrics.widthPixels;
        diameter = width;
        if (height < width){
            diameter = height;
        }
        offset = (int) (0.32*diameter);
        diameter -= offset;
        String imageName = protocol+draw;
    }

    //setup drawing
    private void setupDrawing(){

        //prepare for drawing and setup paint stroke properties
        drawPath = new Path();
        drawPaint = new Paint();
        drawPaint.setColor(paintColor);
        drawPaint.setAntiAlias(true);
        drawPaint.setStrokeWidth(5);
        drawPaint.setStyle(Paint.Style.STROKE);
        drawPaint.setStrokeJoin(Paint.Join.ROUND);
        drawPaint.setStrokeCap(Paint.Cap.ROUND);
        canvasPaint = new Paint(Paint.DITHER_FLAG);
    }

    //size assigned to view
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        drawCanvas = new Canvas(canvasBitmap);
    }

    //draw the view - will be called after touch event
    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
        canvas.drawPath(drawPath, drawPaint);

        canvas.drawRect(width/2 - diameter/2 ,
                (70),
                width/2 + diameter/2,
                1100, drawPaint);
    }

这是我用来清屏的代码，但按下按钮什么也没显示：

public void restoreDraw () {
        drawPath = null;
        canvasBitmap = Bitmap.createBitmap(width, 350, Bitmap.Config.ARGB_8888);
        drawPath = new Path();
    }

我应该清除位图画布，对吗？

【问题讨论】：

标签： java android canvas draw

【解决方案1】：

您必须在 restoreDraw() 方法中添加 requestLayout()。

public void restoreDraw () {
    drawPath = null;
    canvasBitmap = Bitmap.createBitmap(width, 350, Bitmap.Config.ARGB_8888);
    drawPath = new Path();
    requestLayout();
}

【讨论】：