安卓回放功能

Question

用Picture类记录绘制过程，初学者在看了文档后自己试验了一下，不清楚是否能实现效果，且一直出现程序停止运行的错误。

• 功能 点击回放按钮重新绘制过程

【MainActivity】

package painter.com.gangbi;

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    private Button btn;
    DrawView drawView = (DrawView) findViewById(R.id.draw);







    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        btn= (Button) findViewById(R.id.btn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                drawView.mCanvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
                drawView.playBack();



            }
        });



    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.

        switch (item.getItemId()) {

            // 设置id为menu_exit的菜单子项所要执行的方法。
            case R.id.menu1_sub1:
                drawView.mOutterPaint.setStrokeWidth(5);
                break;
            case R.id.menu1_sub2:
                drawView.mOutterPaint.setStrokeWidth(10);
                break;
            case R.id.menu1_sub3:
                drawView.mOutterPaint.setStrokeWidth(20);
                break;
            case R.id.menu1_sub4:
                drawView.mOutterPaint.setStrokeWidth(50);
                break;
            case R.id.menu2:
                drawView.mOutterPaint.setColor(Color.BLACK);
                break;
            case R.id.menu3:
                drawView.mCanvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);



                break;
            case R.id.menu4_sub1:
                drawView.mOutterPaint.setColor(Color.BLACK);
                break;
            case R.id.menu4_sub2:
                drawView.mOutterPaint.setColor(Color.RED);
                break;

            case R.id.menu5:
                System.exit(0);// 结束程序
                break;
        }
        return true;


    }

}

【绘制模块】

package painter.com.gangbi;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Picture;
import android.graphics.drawable.PictureDrawable;
import android.os.Environment;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Toast;

import java.io.File;
import java.io.FileOutputStream;

/**
 * Created by admin on 2017/7/25.
 */

public class DrawView extends View {
   
    public Paint mOutterPaint;
    public Path mPath;
    public Canvas mCanvas;
    private Bitmap mBitmap;
    private int mX;
    private int mY;
    private Bitmap bitmap;





    public DrawView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs,0);
    }

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

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




    //获得宽和高
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width=getMeasuredWidth();
        int height=getMeasuredHeight();
        //初始化bitmap，有了bitmap在初始化canvas
        mBitmap=Bitmap.createBitmap(width,height, Bitmap.Config.ARGB_8888);

        mCanvas=new Canvas(mBitmap);
        setupOutPaint();



    }

    //设置绘制path画笔的颜色


    private void setupOutPaint() {
        mOutterPaint.setColor(Color.BLACK);
        //（锯齿
        mOutterPaint.setAntiAlias(true);
        mOutterPaint.setDither(true);
        mOutterPaint.setStrokeJoin(Paint.Join.ROUND);
        mOutterPaint.setStrokeCap(Paint.Cap.ROUND);
        mOutterPaint.setStyle(Paint.Style.STROKE);
        mOutterPaint.setStrokeWidth(20);
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action =event.getAction();
        int x= (int) event.getX();
        int y= (int) event.getY();
        switch(action)
        {
            case MotionEvent.ACTION_DOWN:
                //用户的手开始的时候
                mX=x;
                mY=y;
                //作为起点
                mPath.moveTo(mX,mY);
                break;
            case MotionEvent.ACTION_MOVE:
                //横向移动坐标
                int dx=Math.abs(x-mX);
                int dy=Math.abs(y-mY);
                if(dx>3||dy>3){
                    //大于3px的变化才开始
                    mPath.lineTo(x,y);
                }
                //更新x，y
                mX=x;
                mY=y;
                break;
            case MotionEvent.ACTION_UP:
                mPath.reset();
                break;

            default:
                break;
        }
        invalidate();
        return true;

    }

    @Override
    public void onDraw(Canvas canvas) {

        canvas.drawBitmap(bitmap,0,0,null);
        drawPath();
        //在内存中准备好path，用canvas绘制
        canvas.drawBitmap(mBitmap,0,0,null);
    }

    private void drawPath() {

        mCanvas.drawPath(mPath,mOutterPaint);
    }

    /*初始化操作*/
    public void init() {


        mOutterPaint=new Paint();

        //canvas必须得到控件宽高比再创建
        mPath=new Path();

        bitmap= BitmapFactory.decodeResource(getResources(), R.mipmap.mod);


    }

    public void playBack()

    {
        Picture picture = new Picture();
        Canvas canvas = picture.beginRecording(300, 500);

        canvas.drawPath(mPath,mOutterPaint);
        picture.endRecording();
        canvas.drawPicture(picture);


    }

}

【主要疑惑点】（按照文档根自己的理解写的不知道是否正确）

• 绘制模块中

public void playBack()

    {
        Picture picture = new Picture();
        Canvas canvas = picture.beginRecording(300, 500);

        canvas.drawPath(mPath,mOutterPaint);//思路是用画笔把之前的path重绘一次
        picture.endRecording();
        canvas.drawPicture(picture);//录完后把过程回放


    }

• MainActivity中

btn= (Button) findViewById(R.id.btn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                drawView.mCanvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
                drawView.playBack();



            }
        });

【程序停止运行】Logcat显示Broken Pipe