Android画板功能代码赏析

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

import java.util.Iterator;
import java.util.Vector;



public class HuaBanView extends View {

    
    private Bitmap cacheBitmap;
    
    private Canvas cacheCanvas;
    
    private Paint paint;
    
    private Paint bitmapPaint;
    
    private Path path;
    
    private int height;
    
    private int width;

    
    private float pX;
    
    private float pY;

    
    private int paintColor = Color.RED;
    
    private static Paint.Style paintStyle = Paint.Style.STROKE;
    
    private static int paintWidth = 5;

    private Canvas canvas;

    private Stack pathList = new Stack(); //存放画笔路径

    private Stack removedPathList = new Stack();//存放撤销的路径


    
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        height = h;
        width = w;
        init();
    }

    private void init() {
        cacheBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888);
        cacheCanvas = new Canvas(cacheBitmap);  //保存之前的绘图
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        path = new Path();
        bitmapPaint = new Paint();
        updatePaint();
    }

    private void updatePaint() {
        paint.setColor(paintColor);
        paint.setStyle(paintStyle);
        paint.setStrokeWidth(paintWidth);
    }

    public HuaBanView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

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

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                path = new Path();
                path.moveTo(event.getX(), event.getY());
                pX = event.getX();
                pY = event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                path.quadTo(pX, pY, (event.getX() + pX) / 2, (event.getY() + pY) / 2);
                pX = event.getX();
                pY = event.getY();
                break;
            case MotionEvent.ACTION_UP:
                //拿起手指时才将其画在缓冲bitmap上
                cacheCanvas.drawPath(path, paint);
                pathList.push(path);
                Log.e("xxx", path.toString());
                Log.e("xxx", pathList.size() + "");
                break;
        }
        //onmove的时候也会一直调用绘制实时图形
        invalidate();

        return true;
    }


    @Override
    protected void onDraw(Canvas canvas) {
        this.canvas = canvas;

        Log.e("xxx", "canvas = " + canvas.toString());

        Log.e("xxx", "绘制cacheBitmap");
        //将之前的路径绘图绘制进新的画板上
        canvas.drawBitmap(cacheBitmap, 0, 0, bitmapPaint);

        //绘制最新的一个路径,如果没有这一句也能画上去，只不过是手抬起来才画上去。
        canvas.drawPath(path, paint);

        Log.e("xxx", "绘制最新一个路径");

    }

    
    public void undo() {

        if (pathList != null && pathList.size() > 0) {
            //调用初始化画布函数以清空画布
            init();

            //将路径保存列表中的最后一个元素删除 ,并将其保存在路径删除列表中
            Path drawPath = pathList.pop();
            removedPathList.push(drawPath);

            //将路径保存列表中的路径重绘在画布上
            Log.e("xxx-剩余步数", pathList.size() + "");

            //将路径减少一个画到缓存画布上，再将缓存画布画到显示的画布上。
            for (Path path : pathList.vector) {
                cacheCanvas.drawPath(path, paint);
                this.path = path;
                Log.e("xxx", path.toString());
            }

            invalidate();
        }
    }

    
    public void redo() {
        if (removedPathList.size() > 0) {
            //调用初始化画布函数以清空画布
            init();

            //将路径保存列表中的最后一个元素删除 ,并将其保存在路径删除列表中
            Path drawPath = removedPathList.pop();
            pathList.push(drawPath);

            //将路径保存列表中的路径重绘在画布上
            Iterator iter = pathList.vector.iterator();        //重复保存
            while (iter.hasNext()) {
                Path path = (Path) iter.next();
                cacheCanvas.drawPath(path, paint); //https://www.it610.com/article/1294866028412608512.htm
            }
            invalidate();// 刷新
        }
    }

    
    public void setColor(int color) {
        paintColor = color;
        updatePaint();
    }

    
    public void setPaintWidth(int width) {
        paintWidth = width;
        updatePaint();
    }

    public static final int PEN = 1;
    public static final int PAIL = 2;

    
    public void setStyle(int style) {
        switch (style) {
            case PEN:
                paintStyle = Paint.Style.STROKE;
                break;
            case PAIL:
                paintStyle = Paint.Style.FILL;
                break;
        }
        updatePaint();
    }

}