android学习之绘图和触摸事件结合的小例子

如下图，你点击哪一块区域，程序就会提示你。

里面主要是有MyCircle类完成，MyCircle继承View类，并重写其onDraw函数，onTouchEvent函数。当MyCircle显示时，调用其onDraw()函数，当用户点击时，调用onTouchEvent(MotionEvent event),动作事件中包含了点击的位置信息。根据点击的位置和画圆的位置之间的关系，做出相应的判断。

主界面DrawSimpleCircle的代码：

package com.example.com.njupt.zhb.drawcircle;import android.app.Activity;import android.os.Bundle;import android.util.DisplayMetrics;public class DrawSimpleCircle extends Activity {    @Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);        setContentView(R.layout.activity_draw_simple_circle);DisplayMetrics metrics = new DisplayMetrics();this.getWindowManager().getDefaultDisplay().getMetrics(metrics);// 屏幕的分辨率int width = metrics.widthPixels;int height = metrics.heightPixels;setContentView(new MyCircle(this, width, height));}}

MyCircle类的代码

package com.example.com.njupt.zhb.drawcircle;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Rect;import android.graphics.RectF;import android.view.MotionEvent;import android.view.View;import android.widget.Toast;/*MyCircle继承View类，并重写其onDraw函数，onTouchEvent函数*/class MyCircle extends View {private Context context;/** * 屏幕的宽 */private int width;/** * 屏幕的高 */private int height;/** *  颜色区分区域 */private int[] colors = new int[] { Color.BLACK, Color.BLUE, Color.CYAN,Color.GREEN, Color.GRAY, Color.MAGENTA, Color.RED, Color.LTGRAY};private String[] colorStrs = new String[] {"黑色", "蓝色", "青绿色", "绿色", "灰色", "洋红色", "红色", "浅灰色"};/** * 大园半径 */private float bigR;/** * 小圆半径 */private float litterR;/** * 屏幕中间点的X坐标 */private float centerX;/** * 屏幕中间点的Y坐标 */private float centerY;public MyCircle(Context context, int width, int height) {super(context);this.context = context;this.width = width;this.height = height;setFocusable(true);System.out.println("width="+width+"<---->height="+height);// 设置两个圆的半径bigR = (width - 20)/2;litterR = bigR/2;centerX = width/2;centerY = height/2;}@Overrideprotected void onDraw(Canvas canvas) {// 画背景颜色Paint bg = new Paint();bg.setColor(Color.WHITE);Rect bgR = new Rect(0, 0, width, height);canvas.drawRect(bgR, bg);float start = 0F;Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);for(int i = 0; i < 4; i ++) {//注意一定要先画大圆，再画小圆，不然看不到效果，小圆在下面会被大圆覆盖// 画大圆RectF bigOval = new RectF(centerX - bigR, centerY - bigR, centerX + bigR, centerY + bigR);paint.setColor(colors[i]);canvas.drawArc(bigOval, start, 90, true, paint);// 画小圆RectF litterOval = new RectF(centerX - litterR, centerY - litterR, centerX + litterR, centerY + litterR);paint.setColor(colors[i+2]);canvas.drawArc(litterOval, start, 90, true, paint);start += 90F;}super.onDraw(canvas);}@Overridepublic boolean onTouchEvent(MotionEvent event) {// 获取点击屏幕时的点的坐标float x = event.getX();float y = event.getY();whichCircle(x, y);return super.onTouchEvent(event);}/** * 确定点击的点在哪个圆内 * @param x * @param y */private void whichCircle(float x, float y) {// 将屏幕中的点转换成以屏幕中心为原点的坐标点float mx = x - centerX;float my = y - centerY;float result = mx * mx + my * my;StringBuilder tip = new StringBuilder();tip.append("您点击了");// 高中的解析几何if(result <= litterR*litterR) {// 点击的点在小圆内tip.append("小圆的");tip.append(colorStrs[whichZone(mx, my)+2]);tip.append("区域");} else if(result <= bigR * bigR) {// 点击的点在大圆内tip.append("大圆的");tip.append(colorStrs[whichZone(mx, my)]);tip.append("区域");} else {// 点不在作作区域tip.append("作用区域以外的区域");}Toast.makeText(context, tip, Toast.LENGTH_SHORT).show();}/** * 判断点击了圆的哪个区域 * @param x * @param y * @return */private int whichZone(float x, float y) {// 简单的象限点处理// 第一象限在右下角，第二象限在左下角，代数里面的是逆时针，这里是顺时针if(x > 0 && y > 0) {return 0;} else if(x > 0 && y < 0) {return 3;} else if(x < 0 && y < 0) {return 2;} else if(x < 0 && y > 0) {return 1;}return -1;}}