回调

package com.example.drawcircle;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class MyView extends View {

	private int radius = 5;
	private int gap = 50;

	private int pos = 0;
	private int count = 6;

	public MyView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}

	public void setSelecte(int pos) {
		this.pos = pos;
		this.invalidate();
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);

		Paint p = new Paint();
		p.setAntiAlias(true);

		int w = this.getWidth();
		int h = this.getHeight();

		int start_w=(w-(gap*(count-1)))/2; 

		for (int i = 0; i < count; i++){

			int x=start_w + i * gap;
			
			if (pos == i) {
				p.setColor(Color.RED);

				canvas.drawCircle(x, h / 2, radius + 5, p);
			} else {
				p.setColor(Color.LTGRAY);

				canvas.drawCircle(x, h / 2, radius, p);
			}
		}

	}
}

<RelativeLayout 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="com.example.drawcircle.MainActivity" >

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/ic_launcher" />

    <com.example.drawcircle.MyView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"        
        android:background="@android:color/transparent" />

</RelativeLayout>