ViewPager加载大量图片

比如说当我们加载100张图片的时候，我们创建100个Imageview，然后放入集合，这样做很容易内存溢出或者加载速度特别慢。我们可以滑动的时候去加载，滑动一张创建一个Imageview

package krelve.view;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
import android.widget.ImageView;
import com.nostra13.universalimageloader.cache.disc.naming.Md5FileNameGenerator;
import com.nostra13.universalimageloader.core.DisplayImageOptions;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;
import com.nostra13.universalimageloader.core.assist.QueueProcessingType;
import java.util.ArrayList;
import java.util.List;

public class Kanner extends FrameLayout
{
private int count;
private String[] imagesUrls;
private ImageLoader mImageLoader;
private List<ImageView> imageViews;
private Context context;
private ViewPager vp;
private int postion;
private DisplayImageOptions options;
public Kanner(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
this.context = context;
initImageLoader(context);
initData();
}
public Kanner(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public Kanner(Context context) {
this(context, null);
}
private void initData() {
imageViews = new ArrayList<ImageView>();
}

public void setImagesUrl(String[] imagesUrl,int postion) {

this.postion = postion;
initLayout();
initImgFromNet(imagesUrl);
showTime();
}

private void initLayout()
{
imageViews.clear();
View view = LayoutInflater.from(context).inflate(R.layout.kanner_layout, this, true);
vp = (ViewPager) view.findViewById(R.id.vp);
}

private void initImgFromNet(String[] imagesUrl) {

imagesUrls = imagesUrl;

count = imagesUrl.length;
// 添加事件监听
initListener();

}

private void initListener()
{
vp.setOnPageChangeListener(new OnPageChangeListener()
{
boolean isScrolled = false;
@Override
public void onPageScrollStateChanged(int status)
{
switch (status)
{
case 1:// 手势滑动
isScrolled = false;
break;
case 2:// 界面切换
isScrolled = true;
break;
case 0:// 滑动结束
// 当前为最后一张，此时从右向左滑，则切换到第一张
if (vp.getCurrentItem() == vp.getAdapter().getCount() - 1 && !isScrolled)
{
vp.setCurrentItem(0);
}
// 当前为第一张，此时从左向右滑，则切换到最后一张
else if (vp.getCurrentItem() == 0 && !isScrolled)
{
vp.setCurrentItem(vp.getAdapter().getCount() - 1);
}
break;
}
}

@Override
public void onPageScrolled(int arg0, float arg1, int arg2)
{

}

@Override
public void onPageSelected(int index)
{

}
});
}

private void showTime()
{
vp.setAdapter(new KannerPagerAdapter());
vp.setCurrentItem(postion);
}

public void initImageLoader(Context context) {
ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(
context).threadPriority(Thread.NORM_PRIORITY - 2)
.denyCacheImageMultipleSizesInMemory()
.diskCacheFileNameGenerator(new Md5FileNameGenerator())
.tasksProcessingOrder(QueueProcessingType.LIFO)
.writeDebugLogs().build();
ImageLoader.getInstance().init(config);
options = new DisplayImageOptions.Builder()
.cacheInMemory(true)
.cacheOnDisk(true)
.build();
mImageLoader = ImageLoader.getInstance();
}

class KannerPagerAdapter extends PagerAdapter
{
@Override
public int getCount() {
return imagesUrls.length;
}

@Override
public int getItemPosition(Object object) {

if (object != null && imagesUrls != null) {
String resId = (String)((ImageView)object).getTag();
if (resId != null) {
for (int i = 0; i < imagesUrls.length; i++) {
if (resId.equals(imagesUrls[i])) {
return i;
}
}
}
}

return POSITION_NONE;
}

@Override
public boolean isViewFromObject(View arg0, Object arg1)
{
return arg0 == arg1;
}

@Override
public Object instantiateItem(ViewGroup container, int position) {

if (imagesUrls != null && position < imagesUrls.length) {
String resId = imagesUrls[position];
if (resId != null) {
ImageView itemView = new ImageView(context);
itemView.setScaleType(ImageView.ScaleType.FIT_XY);
BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 4;
Bitmap bm = BitmapFactory.decodeFile(resId, options);
itemView.setImageBitmap(bm);
itemView.setTag(resId);
((ViewPager) container).addView(itemView);
return itemView;
}
}
return null;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (object != null) {
ViewGroup viewPager = ((ViewGroup) container);
int count = viewPager.getChildCount();
for (int i = 0; i < count; i++) {
View childView = viewPager.getChildAt(i);
if (childView == object) {
viewPager.removeView(childView);
break;
}
}
}

}
}
}