[Android]最省内存的ViewPager添加小圆点指示器

原理：

这个你可以用View叠加来实现，但是这个效果不太理想，1占内存，而移植起来不方便，需要找各种资源，所以采用自己绘制更好，方便，而且效率高。

解决方案：

package com.youtu.view;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.View;

public class ADView extends ViewPager {

AdAdapter mAdAdapter;
Context context;
Paint paint;
List<Map<String, String>> urls;

public ADView(Context context, AttributeSet attrs) {
super(context, attrs);
this.context = context;
paint = new Paint();
InitAdapter();
}

private void InitAdapter() {
urls = new ArrayList<Map<String, String>>();
mAdAdapter = new AdAdapter(context, urls);
this.setAdapter(mAdAdapter);
}

public void setData(List<Map<String, String>> data) {
urls.clear();
for (int i = 0; i < data.size(); i++) {
urls.add(data.get(i));
}
if(urls.size()>0){
this.setVisibility(View.VISIBLE);
}else{
this.setVisibility(View.GONE);
}
mAdAdapter.notifyDataSetChanged();
}

@Override
public void draw(Canvas canvas) {
super.draw(canvas);
drawCycle(canvas);
}

private void drawCycle(Canvas canvas) {
canvas.save();
canvas.translate(getScrollX(), getScrollY());
int count = 0;
if (this.getAdapter() != null) {
count = this.getAdapter().getCount();
}
int select = getCurrentItem();
float density = getContext().getResources().getDisplayMetrics().density;
int itemWidth = (int) (11 * density);
int itemHeight = itemWidth / 2;
int x = (getWidth() - count * itemWidth)/2;
int y = getHeight() - itemWidth;
int minItemHeight = (int) ((float) itemHeight * 0.8F);
paint.setAntiAlias(true);

paint.setStyle(Style.FILL);
for (int i = 0; i < count; i++) {
if (select == i) {
paint.setColor(0xFFbdbdbd);
canvas.drawCircle(x + itemWidth * i + itemWidth / 2, y, minItemHeight, paint);
} else {
paint.setColor(0xFFe6e6e6);
canvas.drawCircle(x + itemWidth * i + itemWidth / 2, y, minItemHeight, paint);
}
}
canvas.restore();
}

}