一周小结（三）——Android版“啥是佩奇”

    “故欲胜人者，必先自胜；欲论人者，必先自论；欲知人者，必先自知。”——《吕氏春秋·先己》。人生在世，经常去和别人比较，但是“人比人，气死人”，我觉得还是要把更多的精力放在自己身上，每天能战胜昨天的自己就是一个不错的进步！

    言归正传，最近研究了研究（其实就是花了一点时间看了看）自定义View，心想能不能做一个有意思的东西，于是Android涂鸦板就产生了！

    其实还是比较简单的，主要就是手指按下、手指移动以及手指抬起这三个事件。

    首先，在构造方法中定义一个幕布——Bitmap，用于存储图画，以便于保存。

WindowManager wm = (WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE);
screenWidth = wm.getDefaultDisplay().getWidth();
screenHeight = wm.getDefaultDisplay().getHeight();
mBitmap = Bitmap.createBitmap(screenWidth, screenHeight, Bitmap.Config.ARGB_8888);

    并且设置好画笔：

mCanvas = new Canvas(mBitmap);
mCanvas.drawColor(Color.YELLOW);
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);// 设置外边缘
mPaint.setStrokeCap(Paint.Cap.ROUND);// 形状
mPaint.setStrokeWidth(10);// 画笔宽度
mPaint.setColor(Color.RED);

    编写事件的代码，主要是按下时初始化path，移动时实时画出，抬起时将path保存，这也是为实现撤销和重做两个功能 奠定基础。

@Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 每次down下去重新new一个Path
                mPath = new Path();
                //每一次记录的路径对象是不一样的
                dp = new DrawPath();
                dp.path = mPath;
                dp.paint = mPaint;
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
        }
        return true;
    }

    private void touch_start(float x, float y) {
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void touch_move(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(mY - y);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            // 从x1,y1到x2,y2画一条贝塞尔曲线，更平滑(直接用mPath.lineTo也是可以的)
            mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
            mX = x;
            mY = y;
        }
    }

    private void touch_up() {
        mPath.lineTo(mX, mY);
        mCanvas.drawPath(mPath, mPaint);
        //将一条完整的路径保存下来(相当于入栈操作)
        savePath.add(dp);
        mPath = null;// 重新置空
    }

    @Override
    public void onDraw(Canvas canvas) {
        canvas.drawColor(0xFFAAAAAA);
        // 将前面已经画过得显示出来
        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        if (mPath != null) {
            // 实时的显示
            canvas.drawPath(mPath, mPaint);
        }
    }

    实现撤销和重做功能：

/**
     * 撤销的核心思想就是将画布清空，
     * 将保存下来的Path路径最后一个移除掉，
     * 重新将路径画在画布上面。
     */
    public void undo() {
        if (savePath != null && savePath.size() > 0) {
            savePath.remove(savePath.size() - 1);
            redrawOnBitmap();
        }
    }

    /**
     * 重做
     */
    public void redo() {
        if (savePath != null && savePath.size() > 0) {
            savePath.clear();
            redrawOnBitmap();
        }
    }

    private void redrawOnBitmap() {
        mBitmap = Bitmap.createBitmap(screenWidth, screenHeight,Bitmap.Config.ARGB_8888);
        mCanvas.setBitmap(mBitmap);// 重新设置画布，相当于清空画布
        Iterator<DrawPath> iter = savePath.iterator();
        while (iter.hasNext()) {
            DrawPath drawPath = iter.next();
            mCanvas.drawPath(drawPath.path, drawPath.paint);
        }
        invalidate();// 刷新
    }

    保存图片的逻辑和JNI实战（一）实现山寨版美图软件中的是一样的：

public void saveToSDCard() {
        final String fileUrl = Environment.getExternalStorageDirectory().toString() + "/android/data/test.png";
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    FileOutputStream fos = new FileOutputStream(new File(fileUrl));
                    mBitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
                    fos.flush();
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

    最后，试一试成果——手画佩奇，由于是用手机画，不太好控制，所以很一般，献丑了！

参考：

1、http://www.noobyard.com/article/p-dtplnwed-er.html

2、 https://www.jianshu.com/p/d5b62c4115de

最后附上自定义控件的全部代码：

package com.example.data.page;

import android.Manifest;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.os.Environment;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * Created by Data on 2019/3/7.
 */

public class CustomView extends View {

    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Path mPath;
    private Paint mBitmapPaint;// 画布的画笔
    private Paint mPaint;// 真实的画笔
    private float mX, mY;// 临时点坐标
    private static final float TOUCH_TOLERANCE = 4;

    // 保存Path路径的集合,用List集合来模拟栈
    private static List<DrawPath> savePath;
    // 记录Path路径的对象
    private DrawPath dp;

    private int screenWidth, screenHeight;

    private class DrawPath {
        public Path path;// 路径
        public Paint paint;// 画笔
    }

    public CustomView(Context context) {
        super(context);
    }

    public CustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        WindowManager wm = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
        screenWidth = wm.getDefaultDisplay().getWidth();
        screenHeight = wm.getDefaultDisplay().getHeight();
        mBitmap = Bitmap.createBitmap(screenWidth, screenHeight, Bitmap.Config.ARGB_8888);
        // 保存一次一次绘制出来的图形
        mCanvas = new Canvas(mBitmap);
        mCanvas.drawColor(Color.YELLOW);
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);// 设置外边缘
        mPaint.setStrokeCap(Paint.Cap.ROUND);// 形状
        mPaint.setStrokeWidth(10);// 画笔宽度
        mPaint.setColor(Color.RED);

        savePath = new ArrayList<DrawPath>();
    }

    @Override
    public void onDraw(Canvas canvas) {
        canvas.drawColor(0xFFAAAAAA);
        // 将前面已经画过得显示出来
        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        if (mPath != null) {
            // 实时的显示
            canvas.drawPath(mPath, mPaint);
        }
    }

    private void touch_start(float x, float y) {
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void touch_move(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(mY - y);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            // 从x1,y1到x2,y2画一条贝塞尔曲线，更平滑(直接用mPath.lineTo也是可以的)
            mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
            mX = x;
            mY = y;
        }
    }

    private void touch_up() {
        mPath.lineTo(mX, mY);
        mCanvas.drawPath(mPath, mPaint);
        //将一条完整的路径保存下来(相当于入栈操作)
        savePath.add(dp);
        mPath = null;// 重新置空
    }

    /**
     * 撤销的核心思想就是将画布清空，
     * 将保存下来的Path路径最后一个移除掉，
     * 重新将路径画在画布上面。
     */
    public void undo() {
        if (savePath != null && savePath.size() > 0) {
            savePath.remove(savePath.size() - 1);
            redrawOnBitmap();
        }
    }

    /**
     * 重做
     */
    public void redo() {
        if (savePath != null && savePath.size() > 0) {
            savePath.clear();
            redrawOnBitmap();
        }
    }

    private void redrawOnBitmap() {
        mBitmap = Bitmap.createBitmap(screenWidth, screenHeight,Bitmap.Config.ARGB_8888);
        mCanvas.setBitmap(mBitmap);// 重新设置画布，相当于清空画布
        Iterator<DrawPath> iter = savePath.iterator();
        while (iter.hasNext()) {
            DrawPath drawPath = iter.next();
            mCanvas.drawPath(drawPath.path, drawPath.paint);
        }
        invalidate();// 刷新
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 每次down下去重新new一个Path
                mPath = new Path();
                //每一次记录的路径对象是不一样的
                dp = new DrawPath();
                dp.path = mPath;
                dp.paint = mPaint;
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
        }
        return true;
    }

    public void saveToSDCard() {
        final String fileUrl = Environment.getExternalStorageDirectory().toString() + "/android/data/test.png";
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    FileOutputStream fos = new FileOutputStream(new File(fileUrl));
                    mBitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
                    fos.flush();
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}