通过弱引用及静态内部类减少内存泄漏问题

我们在开发app时，经常会使用静态内部类。在使用Handler类时，若不定义一个静态Handler子类，在使用是会提示This Handler class should be static or leaks might occur。就是说Handler类需要定义为静态类，否则可能会出现内存泄漏。

 

一般的解决办法如下：

1、定义一个静态内部类，继承自Handler

2、在静态内部类声明一个弱引用

 

下面通过一个下载图片功能的Activity例子来说明：

/**

 * 解决This Handler class should be static or leaks might occur 问题

 *

 */

public class HandlerLeakResolverActivity extends Activity {

	private static final String uri = "http://ww4.sinaimg.cn/bmiddle/786013a5jw1e7akotp4bcj20c80i3aao.jpg";

	private ImageView imageView;

	private Handler handler = new MyHandler(this);

	private ProgressDialog dialog;

	private static final Integer FINISHED = 1;

	

	@Override

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);

		setContentView(R.layout.image_load_layout);

		

		imageView = (ImageView) findViewById(R.id.imageView1);

		Button downloadImg = (Button) findViewById(R.id.btn_downloadImg);

		dialog = new ProgressDialog(this);

		dialog.setMessage("正在下载，请稍后...");

		dialog.setCancelable(false);

		

		downloadImg.setOnClickListener(new OnClickListener() {

			@Override

			public void onClick(View v) {

				imageView.setImageBitmap(null);

				// 启动新activity下载，可以显示图片

				new DownloadThread().start();

				dialog.show();

			}

		});

	}



	/**

	 * 自定义线程类，用于异步下载图片

	 * @author Chase

	 *

	 */

	private class DownloadThread extends Thread {

		@Override

		public void run() {

			Bitmap bitmap=null;

			HttpClient httpClient = new DefaultHttpClient();

			HttpGet httpGet = new HttpGet(uri);

			HttpResponse httpResponse = null;

			try {

				httpResponse = httpClient.execute(httpGet);

				if (httpResponse.getStatusLine().getStatusCode() == 200) {

					byte[] data = EntityUtils.toByteArray(httpResponse

							.getEntity());

					bitmap=BitmapFactory.decodeByteArray(data, 0, data.length);

					

					Message msg = Message.obtain();

					msg.obj = bitmap;

					msg.what = FINISHED;

					handler.sendMessage(msg);

				}

			} catch (Exception e) {

				Log.e(this.getClass().getName(),"图片下载出错！",e);

			}

		}

	}

	

	/**

	 * 定义一个Handler静态内部类

	 * @author Chase

	 *

	 */

	static class MyHandler extends Handler{

		// Activity的弱引用

		WeakReference<HandlerLeakResolverActivity> reference;

		public MyHandler(HandlerLeakResolverActivity activity) {

			reference = new WeakReference<HandlerLeakResolverActivity>(activity);

		}

		@Override

		public void handleMessage(Message msg) {

			HandlerLeakResolverActivity activity = reference.get();

			if(activity != null){

				if(msg.what == FINISHED){

					Bitmap bmp = (Bitmap)msg.obj;

					activity.imageView.setImageBitmap(bmp);

					activity.dialog.dismiss();

				}

			}

		}

	}

}