import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

import java.util.concurrent.Executors;

public class MySurfaceView extends SurfaceView implements SurfaceHolder.Callback, Runnable {
    private SurfaceHolder mSurfaceHolder;
    private Canvas mCanvas;
    private boolean mIsDrawing;

    // 画笔
    private Paint mPaint;
    // 路径
    private Path mPath;
    // 上次的坐标
    private float mLastX, mLastY;

    private boolean mIsWait = true;
    public MySurfaceView(Context context) {
        this(context, null);
    }

    public MySurfaceView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public MySurfaceView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    /**
     * 初始化
     */
    private void init() {
        // 获取 SurfaceHolder对象
        mSurfaceHolder = getHolder();
        //注册 SurfaceHolder
        mSurfaceHolder.addCallback(this);
        // 设置可以获取焦点
        setFocusable(true);
        // 设置触摸可以获取焦点
        setFocusableInTouchMode(true);
        // 保持屏幕常亮
        this.setKeepScreenOn(true);


        // 初始化画笔
        mPaint = new Paint();
        mPaint.setStrokeWidth(50);
        mPaint.setColor(Color.BLACK);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setAntiAlias(true);
        // 初始化路径
        mPath = new Path();
    }


    // SurfaceView 创建时调用
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mIsDrawing = true;
        // 通过线程池来执行
        Executors.newCachedThreadPool().execute(this);
    }

    // SurfaceView 改变时调用
    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
    }

    // SurfaceView 销毁时调用
    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mIsDrawing = false;
    }

    @Override
    public void run() {
        drawing();
        synchronized (MySurfaceView.this) {
            while (mIsDrawing) {
                if (mIsWait) {
                    try {
                        MySurfaceView.this.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                drawing();
            }
        }
    }

    private void drawing() {
        try {
            // 获取Canvas 画布
            mCanvas = mSurfaceHolder.lockCanvas();
            // 下面进行内容的绘制
            mCanvas.drawColor(Color.WHITE);
            mCanvas.drawPath(mPath, mPaint);
        } finally {
            if (mCanvas != null) {
                mSurfaceHolder.unlockCanvasAndPost(mCanvas);
            }
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // 获取当前触摸事件的坐标
        float x = event.getX();
        float y = event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                synchronized (MySurfaceView.this) {
                    mIsWait = false;
                    MySurfaceView.this.notify();
                }
                // 按下
                mLastX = x;
                mLastY = y;
                mPath.moveTo(mLastX, mLastY);
                break;
            case MotionEvent.ACTION_MOVE:
                // 移动
                float dx = Math.abs(x - mLastX);
                float dy = Math.abs(y - mLastY);
                if (dx >= 3 || dy >= 3) {
                    mPath.quadTo(mLastX, mLastY, (mLastX + x) / 2, (mLastY + y) / 2);
                }
                mLastX = x;
                mLastY = y;
                break;
            case MotionEvent.ACTION_UP:
                // 抬起
                mIsWait = true;
                break;
        }
        return true;
    }


}

需要保存功能，用view截图