Android系统中的处理程序和内存泄漏

Question

请看看下面的代码：

public class MyGridFragment extends Fragment{
    
    Handler myhandler = new Handler() {
        @Override
        public void handleMessage(Message message) {
            switch (message.what) {
                case 2:   
                    ArrayList<HashMap<String,String>> theurls = (ArrayList<HashMap<String,String>>) message.obj;
                    urls.addAll(theurls);
                    theimageAdapter.notifyDataSetChanged();
                    dismissBusyDialog();
                    break;
            }
        }
    }
}

当我使用这样的处理程序时，我收到一个警告“处理程序应该是静态的，否则它很容易发生内存泄漏。有人能告诉我最好的方法是什么吗？

Answer 1

根据ADT 20更改，看起来您应该将其设为静态。

新棉绒检查：

检查以确保片段类是可实例化的。如果您不小心使片段innerclass成为非静态的，或者忘记拥有默认的构造函数，当系统在配置更改后试图重新实例化您的片段时，您可能会遇到运行时错误。

查找处理程序泄漏：此检查确保处理程序内部类不包含对其外部类的隐式引用。

Answer 2

这是我做的一个有用的小类，你可以使用。遗憾的是，它仍然非常冗长，因为不能有匿名的静态内部类。

import java.lang.ref.WeakReference;
import android.os.Handler;
import android.os.Message;

/** A handler which keeps a weak reference to a fragment. According to
 * Android's lint, references to Handlers can be kept around for a long
 * time - longer than Fragments for example. So we should use handlers
 * that don't have strong references to the things they are handling for.
 * 
 * You can use this class to more or less forget about that requirement.
 * Unfortunately you can have anonymous static inner classes, so it is a
 * little more verbose.
 * 
 * Example use:
 * 
 *  private static class MsgHandler extends WeakReferenceHandler<MyFragment>
 *  {
 *      public MsgHandler(MyFragment fragment) { super(fragment); }
 * 
 *      @Override
 *      public void handleMessage(MyFragment fragment, Message msg)
 *      {
 *          fragment.doStuff(msg.arg1);
 *      }
 *  }
 * 
 *  // ...
 *  MsgHandler handler = new MsgHandler(this);
 */
public abstract class WeakReferenceHandler<T> extends Handler
{
    private WeakReference<T> mReference;

    public WeakReferenceHandler(T reference)
    {
        mReference = new WeakReference<T>(reference);
    }

    @Override
    public void handleMessage(Message msg)
    {
        if (mReference.get() == null)
            return;
        handleMessage(mReference.get(), msg);
    }

    protected abstract void handleMessage(T reference, Message msg);
}

Answer 3

我最近在自己的代码中更新了类似的内容。我刚刚将匿名Handler类设为受保护的内部类，Lint警告消失了。看看下面的代码是否适合您：

public class MyGridFragment extends Fragment{

    static class MyInnerHandler extends Handler{
        WeakReference<MyGridFragment> mFrag;

        MyInnerHandler(MyGridFragment aFragment) {
            mFrag = new WeakReference<MyGridFragment>(aFragment);
        }

        @Override
        public void handleMessage(Message message) {
            MyGridFragment theFrag = mFrag.get();
            switch (message.what) {
            case 2:
                ArrayList<HashMap<String,String>> theurls = (ArrayList<HashMap<String,String>>) message.obj;
                theFrag.urls.addAll(theurls);
                theFrag.theimageAdapter.notifyDataSetChanged();
                theFrag.dismissBusyDialog();
                break;
            }//end switch
        }
    }
    MyInnerHandler myHandler = new MyInnerHandler(this);
}

你可能必须改变我把“碎片”放在哪里因为我只能猜测那些引用了什么。