【移动应用开发技术】android 安卓异步加载网络图片与viewpager结合使用示例

【移动应用开发技术】android安卓异步加载网络图片，与viewpager结合使用示例

【1】异步加载图片类AsyncImageLoaderpackage

com.example.testdddleapk.cus;

import

java.io.IOException;

import

java.lang.ref.SoftReference;

import

java.util.HashMap;

import

org.apache.http.HttpEntity;

import

org.apache.http.HttpResponse;

import

org.apache.http.HttpStatus;

import

org.apache.http.client.ClientProtocolException;

import

org.apache.http.client.HttpClient;

import

org.apache.http.client.methods.HttpGet;

import

org.apache.http.impl.client.DefaultHttpClient;

import

org.apache.http.params.CoreConnectionPNames;

import

android.graphics.drawable.Drawable;

import

android.os.Handler;

import

android.os.Message;

/**

*

异步加载图片

*/

public

class

AsyncImageLoader

{

//

软引用，使用内存做临时缓存

（程序退出，或内存不够则清除软引用）

private

HashMap<String,

SoftReference<Drawable>>

p_w_picpathCache;

public

AsyncImageLoader()

{

p_w_picpathCache

=

new

HashMap<String,

SoftReference<Drawable>>();

}

/**

*

定义回调接口

*/

public

interface

ImageCallback

{

public

void

p_w_picpathLoaded(Drawable

p_w_picpathDrawable,

String

p_w_picpathUrl);

}

/**

*

创建子线程加载图片

*

子线程加载完图片交给handler处理（子线程不能更新ui，而handler处在主线程，可以更新ui）

*

handler又交给p_w_picpathCallback，p_w_picpathCallback须要自己来实现，在这里可以对回调参数进行处理

*

@param

p_w_picpathUrl

：须要加载的图片url

*

@param

p_w_picpathCallback：

*

@return

*/

public

Drawable

loadDrawable(final

String

p_w_picpathUrl,final

ImageCallback

p_w_picpathCallback)

{

//如果缓存中存在图片

，则首先使用缓存

if

(p_w_picpathCache.containsKey(p_w_picpathUrl))

{

SoftReference<Drawable>

softReference

=

p_w_picpathCache.get(p_w_picpathUrl);

Drawable

drawable

=

softReference.get();

if

(drawable

!=

null)

{

System.out.println("loadDrawable");

p_w_picpathCallback.p_w_picpathLoaded(drawable,

p_w_picpathUrl);//执行回调

return

drawable;

}

}

/**

*

在主线程里执行回调，更新视图

*/

final

Handler

handler

=

new

Handler()

{

public

void

handleMessage(Message

message)

{

System.out.println("handleMessage");

p_w_picpathCallback.p_w_picpathLoaded((Drawable)

message.obj,

p_w_picpathUrl);

}

};

/**

*

创建子线程访问网络并加载图片

，把结果交给handler处理

*/

new

Thread()

{

@Override

public

void

run()

{

Drawable

drawable

=

loadImageFromUrl(p_w_picpathUrl);

//

下载完的图片放到缓存里

p_w_picpathCache.put(p_w_picpathUrl,

new

SoftReference<Drawable>(drawable));

Message

message

=

handler.obtainMessage(0,

drawable);

handler.sendMessage(message);

}

}.start();

return

null;

}

/**

*

下载图片

（注意HttpClient

和httpUrlConnection的区别）

*/

public

Drawable

loadImageFromUrl(String

url)

{

try

{

HttpClient

client

=

new

DefaultHttpClient();

client.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT,

1000*15);

HttpGet

get

=

new

HttpGet(url);

HttpResponse

response;

response

=

client.execute(get);

if

(response.getStatusLine().getStatusCode()

==

HttpStatus.SC_OK)

{

HttpEntity

entity

=

response.getEntity();

Drawable

d

=

Drawable.createFromStream(entity.getContent(),"src");

return

d;

}

else

{

return

null;

}

}

catch

(ClientProtocolException

e)

{

e.printStackTrace();

}

catch

(IOException

e)

{

e.printStackTrace();

}

return

null;

}

//清除缓存

public

void

clearCache()

{

if

(this.p_w_picpathCache.size()

>

0)

{

this.p_w_picpathCache.clear();

}

}

}【2】pagerAdapter的instantiateItem方法@SuppressLint("NewApi")

@Override

public

Object

instantiateItem(final

ViewGroup

container,

final

int

position)

{

String

url=imgsUrls[position];

Drawable

cachedImage

=

asyncImageLoader.loadDrawable(url,

new

ImageCallback()

{

@SuppressLint("NewApi")

public

void

p_w_picpathLoaded(Drawable

p_w_picpathDrawable,String

p_w_picpathUrl)