Android 画笔演示功能的实现

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实现的一个简单的具有画笔功能的view，代码中注释已经很详细了，在这就不啰嗦了，上代码

package com.example.drawtest;import android.annotation.SuppressLint;import android.content.Context;import android.graphics.*;import android.graphics.Bitmap.Config;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;public class DrawView_old2 extends View {float preX;float preY;private Path path;public Paint paint = null;// 定义一个内存中的图片，该图片将作为缓冲区private Bitmap cacheBitmap = null;// 定义cacheBitmap上的Canvas对象private Canvas cacheCanvas = null;/** 橡皮擦图标 */private Bitmap clear_bitmap;/** 当前状态是否为橡皮擦 */private boolean flag_earser = false;/** 判断是否在触摸屏幕，当手指抬起不绘制橡皮擦图标 */private boolean flag_up = true;public DrawView_old2(Context context, AttributeSet attr) {super(context, attr);// 初始化橡皮擦图标clear_bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.bc_54f);}@SuppressLint("DrawAllocation")@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {// TODO Auto-generated method stubsuper.onMeasure(widthMeasureSpec, heightMeasureSpec);// 创建一个与该View相同大小的缓存区// 无法再构造函数中获取view的宽高cacheBitmap = Bitmap.createBitmap(MeasureSpec.getSize(widthMeasureSpec),MeasureSpec.getSize(heightMeasureSpec), Config.ARGB_8888);cacheCanvas = new Canvas();path = new Path();// 设置cacheCanvas将会绘制到内存中的cacheBitmap上cacheCanvas.setBitmap(cacheBitmap);// 设置画笔的颜色paint = new Paint(Paint.DITHER_FLAG);paint.setColor(Color.RED);// 设置画笔风格paint.setStyle(Paint.Style.STROKE);paint.setStrokeWidth(5);// 反锯齿paint.setAntiAlias(true);paint.setDither(true);paint.setStrokeJoin(Paint.Join.ROUND);paint.setStrokeCap(Paint.Cap.ROUND);}/** * 清空画布 */public void clear() {// 创建一个和DrawView大小相同的透明画布cacheBitmap = Bitmap.createBitmap(this.getWidth(), this.getHeight(),Config.ARGB_8888);cacheCanvas = new Canvas();// 设置cacheCanvas将会绘制到内存中的cacheBitmap上cacheCanvas.setBitmap(cacheBitmap);// 刷新页面invalidate();}/** * 设置画笔 *  * @param color *            设置画笔的颜色 * @param width *            画笔宽度 *  */public void setPaint(int color, int width) {// 设置画笔的颜色paint = new Paint(Paint.DITHER_FLAG);paint.setColor(color);// 设置画笔风格paint.setStyle(Paint.Style.STROKE);paint.setStrokeWidth(5);// 反锯齿paint.setAntiAlias(true);paint.setDither(true);paint.setStrokeJoin(Paint.Join.ROUND);paint.setStrokeCap(Paint.Cap.ROUND);flag_earser = false;}/** * 设置橡皮擦 */public void setEarser() {// 设置橡皮擦画笔Paint cPaint = new Paint();cPaint.setAlpha(0);cPaint.setColor(Color.TRANSPARENT);cPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));cPaint.setAntiAlias(true);cPaint.setDither(true);cPaint.setStyle(Paint.Style.STROKE);cPaint.setStrokeJoin(Paint.Join.ROUND);cPaint.setStrokeCap(Paint.Cap.ROUND);cPaint.setStrokeWidth(60);paint = cPaint;clear_bitmap = Bitmap.createScaledBitmap(clear_bitmap, 60, 60, true);flag_earser = true;}/** * 根据手指移动进行绘图 */@SuppressLint("ClickableViewAccessibility")@Overridepublic boolean onTouchEvent(MotionEvent event) {// 获取拖动事件的发生位置float x = event.getX();float y = event.getY();switch (event.getAction()) {case MotionEvent.ACTION_DOWN: // 手按下flag_up = false;path.moveTo(x, y);preX = x;preY = y;break;case MotionEvent.ACTION_MOVE: // 手移动path.quadTo(preX, preY, (x + preX) / 2, (y + preY) / 2);preX = x;preY = y;break;case MotionEvent.ACTION_UP: // 手放开flag_up = true;cacheCanvas.drawPath(path, paint);path.reset();break;}invalidate();// 返回true表明处理方法已经处理该事件return true;}@SuppressLint("DrawAllocation")@Overrideprotected void onDraw(Canvas canvas) {Paint bmpPaint = new Paint();// 将cacheBitmap绘制到该View组件上canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);// 如果是在橡皮擦状态则画橡皮擦图标if (flag_earser) {if (!flag_up) {canvas.drawBitmap(clear_bitmap, preX - clear_bitmap.getWidth()/ 2, preY - clear_bitmap.getHeight() / 2, null);}// 沿着path绘制// 这里使用cacheCanvas是防止Xfermode绘图出现绘图时黑框cacheCanvas.drawPath(path, paint);} else {// 沿着path绘制,没有这行不会动态绘制canvas.drawPath(path, paint);}}}