该例子我们完成一个跟随手指动的小球
首先建一个DrawView.java的View,里边重写了OnDraw和onTouchEvent方法
package com.example.drawview;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
public class DrawView extends View {
public float currentX=40;
public float currentY=50;
public DrawView(Context context, AttributeSet attrs) {
super(context, attrs);
}
//如果想扩展我们的View就重写我们的onDraw方法
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//创建画笔
Paint p=new Paint();
//设置画笔颜色
p.setColor(Color.RED);
//绘制一个小球
canvas.drawCircle(currentX, currentX, 15, p);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
this.currentX=event.getX();
this.currentY=event.getY();
//通知组件重绘
this.invalidate();
//用true表示处理方法已经处理该事件
return true;
}
}
接下来在我们的activity_main.xml当中定义该组件
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".DrawView"
android:orientation="vertical">
<!-- 使用自定义组件 -->
<com.example.drawview.DrawView
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
</LinearLayout>
Activity.java
Activity类中不需要为该View绑定事件监听器,因为该View自己就可以处理触摸事件
package com.example.drawview;
import android.app.Activity;
import android.os.Bundle;
public class DrawViewTest extends Activity{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}