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 {
@Override
public 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;
}

@Override
protected 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);
}

@Override
public 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;
}

}