如何在TextView上绘制

Question

我是AndroidStudio的新手，想解决一个问题！我需要创建一个可以在文本上方绘制的应用程序，以便突出显示重要单词等！当我创建PaintView类并将backGround设置为TRansparent时，我的clear（）函数不起作用！当背景设置为另一种颜色（例如，白色）时，清除功能将正常工作。有人知道会发生什么吗？

public class PaintView extends View {     
    public static int BRUSH_SIZE = 5;   
    public static final int DEFAULT_COLOR = Color.BLUE;   
    public static final int DEFAULT_BG_COLOR = Color.TRANSPARENT;   
    public static final float TOUCH_TOLERANCE = 4;   
    private  float mX, mY;   
    private Path mPath;   
    private Paint mPaint;   
    private ArrayList<FingerPath> paths= new ArrayList<>();   
    private int currentColor;   
    private int backgroundColor = DEFAULT_BG_COLOR;   
    private int strokeWidth;   
    private boolean emboss;   
    private boolean blur;   
    private MaskFilter mEmboss;   
    private MaskFilter mBlur;   
    private Bitmap mBitmap;   
    private Canvas mCanvas;   
    private Paint mBitmapPaint = new Paint(Paint.DITHER_FLAG);  

    public PaintView(Context context) {
       this(context, null);
    }

    public PaintView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(DEFAULT_COLOR);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setXfermode(null);
        mPaint.setAlpha(0xff);
        float[] direction = new float[]{1, 1, 1};

        mEmboss = new EmbossMaskFilter(direction,0.4f,6f,3.5f);
        mBlur = new BlurMaskFilter(2, BlurMaskFilter.Blur.NORMAL);
    }

    public void init(DisplayMetrics metrics){
        int height = metrics.heightPixels;
        int width = metrics.widthPixels;

        mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);
        currentColor = DEFAULT_COLOR;
        strokeWidth = BRUSH_SIZE;
    }

    public void normal(){
        emboss = false;
        blur = false;
    }

    public void emboss(){
        emboss = true;
        blur = false;
    }

    public void blur(){
        emboss = false;
        blur = true;
    }

    public void clear(){
        if(!paths.isEmpty()) {
            backgroundColor = DEFAULT_BG_COLOR;
            int size = paths.size();
            paths.remove(paths.get(size-1));
            normal();
            invalidate();
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.save();
        mCanvas.drawColor(backgroundColor);

        for(FingerPath fp:paths){
            mPaint.setColor(fp.color);
            mPaint.setStrokeWidth(fp.strokeWidth);
            mPaint.setMaskFilter(null);

            if(fp.emboss)
                mPaint.setMaskFilter(mEmboss);
            else if (fp.blur)
                mPaint.setMaskFilter(mBlur);

            mCanvas.drawPath(fp.path, mPaint);
        }

        canvas.drawBitmap(mBitmap, 0,0,mBitmapPaint);
        canvas.restore();
    }

        private void touchStart(float x, float y){

        mPath = new Path();
        FingerPath fp = new FingerPath(currentColor, emboss, blur, strokeWidth, mPath);
        paths.add(fp);

        mPath.reset();
        mPath.moveTo(x,y);
        mX = x;
        mY = y;
        }

        private void touchMove(float x, float y){
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y-mY);

        if(dx >= TOUCH_TOLERANCE || dy>= TOUCH_TOLERANCE){
            mPath.quadTo(mX, mY, (x+mX)/2, (y+mY)/2);
            mX = x;
            mY = y;
        }
    }

    private void touchUp(){
        mPath.lineTo(mX, mY);
    }

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

        switch (event.getAction()){
            case MotionEvent.ACTION_DOWN:
                touchStart(x,y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touchMove(x,y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touchUp();
                invalidate();
                break;
        }
        return true;
    }
}