解决ListView滑动时卡的问题，实现异步加载图片解决
ListView是最为常见的空间之一，现在的应用的呈现形式大多数都需要用到ListView来呈现，以列表的方式最直观最便于操作。
那么在使用的过程中大家一定使用adapter适配器来匹配这个ListView，问题就来了，如果直接使用sampleAdapter的话，会出现诸多的问题，诸如滚动的时候很卡，特别是每一行都有头像啊什么的，再加上数据量一大，兼职就卡的不行，那么先来说说解决卡的问题的简单的实现方法吧。
首先需要自己来写一个myAdapter继承与BaseAdapter。
然后最关键的是在getView方法中做到以下几点判断convertView是否为空，这样可以避免每次滚动都去新建，可以节约大量资源，同时对于图片采用开启线程以异步加载的方式来加载它，又可以节约一部分资源，同时，将加载下来的图片缓存到本地，当下一次的时候首先读取本地图片，第一可以节约流量，其次速度非常快（不过服务器图片更新了这个要想好解决方案，不然你本地的图片不会被替换掉）。最后就是在滚动时间的时候让异步加载暂停，等手放开的时候再加载，这样可以保证滚动的超级流畅，不过同时会出现滚动比较大的时候图片都还是空的没有加载的现象，反正自己斟酌优劣吧，代码都有哈！接下来上代码了
首先是主activity
package com.challen;
import java.util.Vector;
import cindy.android.test.synclistview.R;
import android.app.Activity;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class TestListViewActivity extends Activity implements
AdapterView.OnItemClickListener {
ListView viewBookList;
BookItemAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
viewBookList = (ListView) findViewById(R.id.viewBookList);
adapter = new BookItemAdapter(this, viewBookList);
viewBookList.setAdapter(adapter);
viewBookList.setOnItemClickListener(this);
reload();
}
private void reload() {
adapter.clean();
// loadStateView.startLoad();
new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(2 * 1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
loadDate();
sendMessage(REFRESH_LIST);
}
}).start();
}
public void loadDate() {
for (int i = 0; i < 100; i++) {
adapter.addBook("我是challen的测试异步加" + i, "1",
"http://ww1.sinaimg.cn/thumbnail/80ab1ad3gw1dx8tfjvbgdj.jpg");
adapter.addBook("小美" + i, "2",
"http://ww2.sinaimg.cn/thumbnail/7f9fd9a9jw1dtyrqrh4mjj.jpg");
adapter.addBook("金总" + i, "3",
"http://ww3.sinaimg.cn/thumbnail/9d57e8e4jw1dx6topumz5j.jpg");
adapter.addBook("创意铺子" + i, "4",
"http://www.pfwx.com/files/article/image/3/3237/3237s.jpg");
adapter.addBook("人名日报" + i, "5",
"http://ww2.sinaimg.cn/thumbnail/9263d293jw1dx8snx58s7j.jpg");
adapter.addBook("名字是乱明的" + i, "6",
"http://tp1.sinaimg.cn/1660452532/50/5646449168/0");
adapter.addBook("帅哥即将出现" + i, "7",
"http://p1.qhimg.com/t01a869bb64c7f3d8c6.png");
adapter.addBook("注意了哦" + i, "8",
"http://www.baidu.com/img/baidu_jgylogo3.gif");
adapter.addBook("来拉" + i, "9",
"http://tp4.sinaimg.cn/2190322767/50/5605436918/1");
adapter.addBook("这个就是我啦" + i, "10",
"http://avatar.csdn.net/E/7/2/3_jkingcl.jpg");
}
}
private static final int REFRESH_LIST = 0x10001;
public static final int SHOW_STR_TOAST = 0;
public static final int SHOW_RES_TOAST = 1;
private Handler pichandler = new Handler() {
@Override
public void handleMessage(Message msg) {
if (!Thread.currentThread().isInterrupted()) {
handleOtherMessage(msg.what);
}
}
};
public void sendMessage(int flag) {
pichandler.sendEmptyMessage(flag);
}
protected void handleOtherMessage(int flag) {
switch (flag) {
case REFRESH_LIST:
adapter.notifyDataSetChanged();
default:
break;
}
}
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
// TODO Auto-generated method stub
}
public class BookItemAdapter extends BaseAdapter {
public class BookModel {
public String book_id;
public String out_book_url;
public String author;
public String book_state_s;
public String leading_role;
public String update_time;
public String book_name;
public String out_book_pic;
public String sort_id;
public String last_update_section_title;
public String last_update_section_url;
public String introduction;
}
private LayoutInflater mInflater;
private Vector<BookModel> mModels = new Vector<BookModel>();
private ListView mListView;
SyncImageLoader syncImageLoader;
public BookItemAdapter(Context context, ListView listView) {
mInflater = LayoutInflater.from(context);
syncImageLoader = new SyncImageLoader();
mListView = listView;
/*
*
* 这一句话取消掉注释的话，那么能更加的节省资源，不过体验稍微有点，
* 你滑动的时候不会读取图片，当手放开后才开始度图片速度更快，你们可以试一试
* */
// mListView.setOnScrollListener(onScrollListener);
}
public void addBook(String book_name, String author, String out_book_pic) {
BookModel model = new BookModel();
model.book_name = book_name;
model.author = author;
model.out_book_pic = out_book_pic;
mModels.add(model);
}
public void clean() {
mModels.clear();
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return mModels.size();
}
@Override
public Object getItem(int position) {
if (position >= getCount()) {
return null;
}
return mModels.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = mInflater.inflate(R.layout.item_adapter,
null);
}
BookModel model = mModels.get(position);
convertView.setTag(position);
ImageView iv = (ImageView) convertView.findViewById(R.id.sItemIcon);
TextView sItemTitle = (TextView) convertView
.findViewById(R.id.sItemTitle);
TextView sItemInfo = (TextView) convertView
.findViewById(R.id.sItemInfo);
sItemTitle.setText(model.book_name);
sItemInfo.setText(model.out_book_url);
// 添加�?��背景在滑动的时�?就会显示背景而不是其他的缓存的照片，用户体验更好
iv.setBackgroundResource(R.drawable.rc_item_bg);
syncImageLoader.loadImage(position, model.out_book_pic,
imageLoadListener, model.author);
return convertView;
}
SyncImageLoader.OnImageLoadListener imageLoadListener = new SyncImageLoader.OnImageLoadListener() {
@Override
public void onImageLoad(Integer t, Drawable drawable) {
// BookModel model = (BookModel) getItem(t);
View view = mListView.findViewWithTag(t);
if (view != null) {
ImageView iv = (ImageView) view
.findViewById(R.id.sItemIcon);
iv.setBackgroundDrawable(drawable);
}
}
@Override
public void onError(Integer t) {
BookModel model = (BookModel) getItem(t);
View view = mListView.findViewWithTag(model);
if (view != null) {
ImageView iv = (ImageView) view
.findViewById(R.id.sItemIcon);
iv.setBackgroundResource(R.drawable.rc_item_bg);
}
}
};
public void loadImage() {
int start = mListView.getFirstVisiblePosition();
int end = mListView.getLastVisiblePosition();
if (end >= getCount()) {
end = getCount() - 1;
}
syncImageLoader.setLoadLimit(start, end);
syncImageLoader.unlock();
}
AbsListView.OnScrollListener onScrollListener = new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
switch (scrollState) {
case AbsListView.OnScrollListener.SCROLL_STATE_FLING:
syncImageLoader.lock();
break;
case AbsListView.OnScrollListener.SCROLL_STATE_IDLE:
loadImage();
break;
case AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
syncImageLoader.lock();
break;
default:
break;
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
}
};
}
}
其次是实现异步加载和缓存图片的功能代码loader.java
package com.challen;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.URL;
import java.util.HashMap;
import android.graphics.drawable.Drawable;
import android.os.Environment;
import android.os.Handler;
public class SyncImageLoader {
private Object lock = new Object();
private boolean mAllowLoad = true;
private boolean firstLoad = true;
private int mStartLoadLimit = 0;
private int mStopLoadLimit = 0;
final Handler handler = new Handler();
private HashMap<String, SoftReference<Drawable>> imageCache = new HashMap<String, SoftReference<Drawable>>();
public interface OnImageLoadListener {
public void onImageLoad(Integer t, Drawable drawable);
public void onError(Integer t);
}
public void setLoadLimit(int startLoadLimit,int stopLoadLimit){
if(startLoadLimit > stopLoadLimit){
return;
}
mStartLoadLimit = startLoadLimit;
mStopLoadLimit = stopLoadLimit;
}
public void restore(){
mAllowLoad = true;
firstLoad = true;
}
public void lock(){
mAllowLoad = false;
firstLoad = false;
}
public void unlock(){
mAllowLoad = true;
synchronized (lock) {
lock.notifyAll();
}
}
public void loadImage(Integer t, String imageUrl,
OnImageLoadListener listener,String author1) {
final OnImageLoadListener mListener = listener;
final String mImageUrl = imageUrl;
final Integer mt = t;
final String author = author1;
new Thread(new Runnable() {
@Override
public void run() {
if(!mAllowLoad){
synchronized (lock) {
try {
lock.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
if(mAllowLoad && firstLoad){
loadImage(mImageUrl, mt, mListener,author);
}
if(mAllowLoad && mt <= mStopLoadLimit && mt >= mStartLoadLimit){
loadImage(mImageUrl, mt, mListener,author);
}
}
}).start();
}
private void loadImage(final String mImageUrl,final Integer mt,final OnImageLoadListener mListener,final String author){
if (imageCache.containsKey(mImageUrl)) {
System.out.println("drawable");
SoftReference<Drawable> softReference = imageCache.get(mImageUrl);
final Drawable d = softReference.get();
if (d != null) {
handler.post(new Runnable() {
@Override
public void run() {
if(mAllowLoad){
mListener.onImageLoad(mt, d);
}
}
});
return;
}
}
try {
final Drawable d = loadImageFromUrl(mImageUrl,author);
if(d != null){
imageCache.put(mImageUrl, new SoftReference<Drawable>(d));
}
handler.post(new Runnable() {
@Override
public void run() {
if(mAllowLoad){
mListener.onImageLoad(mt, d);
}
}
});
} catch (IOException e) {
handler.post(new Runnable() {
@Override
public void run() {
mListener.onError(mt);
}
});
e.printStackTrace();
}
}
public static Drawable loadImageFromUrl(String url,String author) throws IOException {
//是否SD卡可用
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
//检查是或有保存图片的文件夹，没有就穿件一个
String FileUrl = Environment.getExternalStorageDirectory()+"/TestSyncListView/";
File folder = new File(FileUrl);
if(!folder.exists()){
folder.mkdir();
}
File f = new File(FileUrl+author+".jpg");
//SD卡中是否有该文件，有则直接读取返回
if(f.exists()){
FileInputStream fis = new FileInputStream(f);
Drawable d = Drawable.createFromStream(fis, "src");
return d;
}
//没有的话则去连接下载，并写入到SD卡中
URL m = new URL(url);
InputStream i = (InputStream) m.getContent();
DataInputStream in = new DataInputStream(i);
FileOutputStream out = new FileOutputStream(f);
byte[] buffer = new byte[1024];
int byteread=0;
while ((byteread = in.read(buffer)) != -1) {
out.write(buffer, 0, byteread);
}
in.close();
out.close();
Drawable d = Drawable.createFromStream(i, "src");
return loadImageFromUrl(url,author);
}
//SD卡不可用则直接加载使用
else{
URL m = new URL(url);
InputStream i = (InputStream) m.getContent();
Drawable d = Drawable.createFromStream(i, "src");
return d;
}
}
}
最后附上整个测试demo的下载地址，各位可以去下载，然后根据自己的需求加入到自己的项目中，希望可以帮助到大家，大家多多交流哦！
http://download.csdn.net/detail/jkingcl/4726519
