不整虛的，直接上程式碼

public class SignatureView extends View {

    private Context context;
    //X軸起點
    private float x;
    //Y軸起點
    private float y;
    //畫筆
    private final Paint paint = new Paint();
    //路徑
    private final Path path = new Path();
    //畫布
    private Canvas canvas;
    //生成的圖片
    private
 
 Bitmap bitmap;
    //畫筆的寬度
    private int paintWidth = 10;
    //簽名顏色
    private int paintColor = Color.BLACK;
    //背景顏色
    private int backgroundColor = Color.WHITE;
    //是否已經簽名
    private boolean isTouched = false;

    //簽名開始與結束
    public interface Touch {
        void OnTouch(boolean isTouch);
    }
 


    private Touch touch;


    public SignatureView(Context context) {
        super(context);
        init(context);
    }

    public SignatureView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public SignatureView(Context context,
 
 @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    private void init(Context context) {
        this.context = context;
        //抗鋸齒
        paint.setAntiAlias(true);
        //樣式
        paint.setStyle(Paint.Style.STROKE);
        //畫筆顏色
        paint.setColor(paintColor);
        //畫筆寬度
        paint.setStrokeWidth(paintWidth);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        //創建於view大小一致的bitmap
        bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
        canvas = new Canvas(bitmap);
        canvas.drawColor(backgroundColor);
        isTouched = false;
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (touch != null) touch.OnTouch(true);
        switch (event.getAction()) {
            //手指按下
            case MotionEvent.ACTION_DOWN:
                touchDwon(event);
                break;
            //手指移動
            case MotionEvent.ACTION_MOVE:
                isTouched = true;
                if (touch != null) touch.OnTouch(false);
                touchMove(event);
                break;
            //手指抬起
            case MotionEvent.ACTION_UP:
                canvas.drawPath(path, paint);
                path.reset();
                break;
        }
        // 更新繪製
        invalidate();
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //畫此次筆畫之前的簽名
        canvas.drawBitmap(bitmap, 0, 0, paint);
        // 通過畫布繪製多點形成的圖形
        canvas.drawPath(path, paint);
    }


    //手指按下的方法
    private void touchDwon(MotionEvent event) {
        //重置繪製路徑
        path.reset();
        float downX = event.getX();
        float downY = event.getY();
        x = downX;
        y = downY;
        //繪製起點
        path.moveTo(downX, downY);
    }

    //手指滑動的方法
    private void touchMove(MotionEvent event) {
        //當前的x,y座標點
        final float moveX = event.getX();
        final float moveY = event.getY();
        //之前的x,y座標點
        final float previousX = x;
        final float previousY = y;
        //獲取絕對值
        final float dx = Math.abs(moveX - previousX);
        final float dy = Math.abs(moveY - previousY);
        if (dx >= 3 || dy >= 3) {
            float cX = (moveX + previousX) / 2;
            float cY = (moveY + previousY) / 2;
            path.quadTo(previousX, previousY, cX, cY);
            x = moveX;
            y = moveY;
        }
    }

    /**
     * 設定畫筆顏色
     *
     * @param paintColor
     */
    public void setPaintColor(int paintColor) {
        this.paintColor = paintColor;
        paint.setColor(paintColor);
    }

    /**
     * 設定畫筆寬度
     *
     * @param paintWidth
     */
    public void setPaintWidth(int paintWidth) {
        this.paintWidth = paintWidth;
        paint.setStrokeWidth(paintWidth);
    }

    /**
     * 設定畫板顏色
     *
     * @param canvasColor
     */
    public void setCanvasColor(int canvasColor) {
        this.backgroundColor = canvasColor;
    }


    /**
     * 清除畫板
     */
    public void clear() {
        if (canvas != null) {
            isTouched = false;
            //更新畫板
            paint.setColor(paintColor);
            paint.setStrokeWidth(paintWidth);
            canvas.drawColor(backgroundColor, PorterDuff.Mode.CLEAR);
            invalidate();
        }
    }

    /**
     * 獲取畫板的Bitmap
     *
     * @return
     */
    public Bitmap getBitmap() {
        setDrawingCacheEnabled(true);
        buildDrawingCache();
        Bitmap bitmap = getDrawingCache();
        setDrawingCacheEnabled(false);
        return bitmap;
    }

    /**
     * 是否有簽名
     *
     * @return
     */
    public Boolean getSigstatus() {
        return isTouched;
    }

    /**
     * 儲存畫板
     *
     * @param path 儲存到路徑
     */
    @SuppressLint("WrongThread")
    public Boolean save(String path) throws IOException {
        Bitmap bitmap = this.bitmap;
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.PNG, 100, bos);
        byte[] buffer = bos.toByteArray();
        if (buffer != null) {
            File file = new File(path);
            if (file.exists()) {
                file.delete();
            }
            OutputStream outputStream = new FileOutputStream(file);
            outputStream.write(buffer);
            outputStream.close();
            return true;
        } else {
            return false;
        }
    }
    public Bitmap returnBitmap() {
        return this.bitmap;
    }
}

效果圖