LeakCanary DialogFragment 泄漏检测

Question

每次我尝试显示 DialogFragment 时都会出现内存泄漏。

这是我的测试对话框（取自 android 开发者页面）的样子：

public class TestDialog extends DialogFragment {

    public static TestDialog newInstance(int title) {
        TestDialog frag = new TestDialog();
        Bundle args = new Bundle();
        args.putInt("title", title);
        frag.setArguments(args);
        return frag;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        int title = getArguments().getInt("title");

        return new AlertDialog.Builder(getActivity())
                .setIcon(R.drawable.ic_action_about)
                .setTitle(title)
                .setPositiveButton(R.string.ok,
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int whichButton) {
                                //((FragmentAlertDialog)getActivity()).doPositiveClick();
                            }
                        }
                )
                .setNegativeButton(R.string.cancel,
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int whichButton) {
                                //((FragmentAlertDialog)getActivity()).doNegativeClick();
                            }
                        }
                )
                .create();
    }
}

我使用以下在按钮按下时执行的代码启动它：

DialogFragment newFragment = TestDialog.newInstance(R.string.company_title);
newFragment.show(getFragmentManager(), "dialog");

这是最好的部分：

如何解决此泄漏（或至少隐藏它，因为 canaryleak 对所有这些通知都感到非常烦人）？

Answer 1

造成这次泄露的原因是DialogFragment的源代码：

@Override
    public void onActivityCreated(Bundle savedInstanceState) {
        ...
        // other codes
        ...
        mDialog.setCancelable(mCancelable);
        // hear is the main reason
        mDialog.setOnCancelListener(this);
        mDialog.setOnDismissListener(this);
        ...
        // other codes
        ...
    }

让我们看看函数Dialog.SetOnCancelListener(DialogInterface.OnCancelListener)发生了什么：

/**
     * Set a listener to be invoked when the dialog is canceled.
     *
     * <p>This will only be invoked when the dialog is canceled.
     * Cancel events alone will not capture all ways that
     * the dialog might be dismissed. If the creator needs
     * to know when a dialog is dismissed in general, use
     * {@link #setOnDismissListener}.</p>
     * 
     * @param listener The {@link DialogInterface.OnCancelListener} to use.
     */
    public void setOnCancelListener(@Nullable OnCancelListener listener) {
        if (mCancelAndDismissTaken != null) {
            throw new IllegalStateException(
                    "OnCancelListener is already taken by "
                    + mCancelAndDismissTaken + " and can not be replaced.");
        }
        if (listener != null) {
            // here
            mCancelMessage = mListenersHandler.obtainMessage(CANCEL, listener);
        } else {
            mCancelMessage = null;
        }
    }

还有，这里是Handler.obtainMessage(int, Object)的源代码：

    /**
     * 
     * Same as {@link #obtainMessage()}, except that it also sets the what and obj members 
     * of the returned Message.
     * 
     * @param what Value to assign to the returned Message.what field.
     * @param obj Value to assign to the returned Message.obj field.
     * @return A Message from the global message pool.
     */
    public final Message obtainMessage(int what, Object obj)
    {
        return Message.obtain(this, what, obj);
    }

最后会调用函数Message.obtain(Handler, int, Object)：

    /**
     * Same as {@link #obtain()}, but sets the values of the <em>target</em>, <em>what</em>, and <em>obj</em>
     * members.
     * @param h  The <em>target</em> value to set.
     * @param what  The <em>what</em> value to set.
     * @param obj  The <em>object</em> method to set.
     * @return  A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what, Object obj) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.obj = obj;

        return m;
    }

我们可以看到cancelMessage持有DialogFragment的实例，导致内存泄漏。我只是想让你知道这一点，除了不要使用DialogFragment，我没有办法避免它。或者有更好解决方案的人请告诉我。

Answer 2

万一有人仍然遇到这个问题：我通过将leakcanary 更新到最新版本（此时为2.4）解决了这个问题。似乎这是一个误报检测。我使用的是leakcanary 2.0beta-3。

Answer 3

基于@EmMper 的回答。如果您不需要 onCancelListener，这是一种解决方法。

import android.app.Activity
import android.os.Bundle
import androidx.annotation.MainThread
import androidx.fragment.app.DialogFragment

open class PatchedDialogFragment : DialogFragment() {

    @MainThread
    override fun onActivityCreated(savedInstanceState: Bundle?) {
        // Fixing the issue described here
        // https://stackoverflow.com/questions/53185154/leakcanary-dialogfragment-leak-detection
        val initialShowsDialog = showsDialog
        showsDialog = false
        super.onActivityCreated(savedInstanceState)
        showsDialog = initialShowsDialog

        if (!showsDialog) {
            return
        }
        val view = view
        if (view != null) {
            check(view.parent == null) { "DialogFragment can not be attached to a container view" }
            dialog!!.setContentView(view)
        }
        val activity: Activity? = activity
        if (activity != null) {
            dialog!!.ownerActivity = activity
        }
        dialog!!.setCancelable(isCancelable)
        if (savedInstanceState != null) {
            val dialogState =
                savedInstanceState.getBundle("android:savedDialogState")
            if (dialogState != null) {
                dialog!!.onRestoreInstanceState(dialogState)
            }
        }
    }
}

只需扩展 PatchedDialogFragment 而不是 DialogFragment。

Answer 4

我通过从我的自定义 DialogFragment 实现中删除 OnDismissListener 和 OnCancelListener 来消除此泄漏。 我还必须将 null 传递给否定按钮侦听器：.setNegativeButton(R.string.cancel, null)。