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")
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		// TODO Auto-generated method stub
		super.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")
	@Override
	public 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")
	@Override
	protected 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);
		}
	}

}