原文地址：https://www.jianshu.com/p/db2946b0b217
(1)dialogfragment展示时引起的崩溃问题
(2)内存泄露问题
(3)加载含有fragment的view导致的崩溃
dialogfragment展示时引起的崩溃问题
这个问题比较简单，就是在dialogfragment要展示的时候，如果按home键返回到了桌面，这时强行调用show方法就会导致app崩溃，抛出的异常大致如下
java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
熟悉fragment应该都知道，这是一个fragment导致的崩溃，可以通过调用commitAllowingStateLoss方法来避免崩溃。出现这种崩溃场景常见的比如app首页进入后可能会弹出一些弹框广告，这些弹框如果在网络有一定延迟并且app返回到home后触发弹框，如果app没有做好处理就会导致崩溃，可以来看下dialogfragment相关的show方法
public void show(FragmentManager manager, String tag) {
this.mDismissed = false;
this.mShownByMe = true;
FragmentTransaction ft = manager.beginTransaction();
ft.add(this, tag);
ft.commit();
}
可以很明显的看到，并没有调用commitAllowingStateLoss，而是直接调用了commit方法。但是去翻看下dialogfragment的dismiss方法，你却会发现
void dismissInternal(boolean allowStateLoss) {
if (!this.mDismissed) {
this.mDismissed = true;
this.mShownByMe = false;
if (this.mDialog != null) {
this.mDialog.dismiss();
}
this.mViewDestroyed = true;
if (this.mBackStackId >= 0) {
this.getFragmentManager().popBackStack(this.mBackStackId, 1);
this.mBackStackId = -1;
} else {
FragmentTransaction ft = this.getFragmentManager().beginTransaction();
ft.remove(this);
if (allowStateLoss) {
ft.commitAllowingStateLoss();
} else {
ft.commit();
}
}
}
}
有相关调用commitAllowingStateLoss的方法，show的时候不允许commitAllowingStateLoss但是dismiss却又允许commitAllowingStateLoss，不太理解google大佬这么做的意图。既然问题根源找到了那么问题就好解决了，主要有两个方法
(1)app代码逻辑控制，在app返回home之后如果有相关的弹框就先屏蔽掉，等app重新展示再弹框。这个方法改动比较大，可能需要对弹框逻辑进行修改，不太推荐
(2)给dialogfragment增加调用commitAllowingStateLoss的方法，目前自己采用的方法，通过修改dialograment的show方法源码即可
2 内存泄露问题
这个应该说是使用dialogfragment遇到的比较多的一个问题，产生泄露的原因和内部使用的dialog有关以及一些三方库线程中使用到message有关，要把这个问题说明白首先看下和handler相关的message，这似乎回到了内存泄露的经典场景handler+message。但dialogfragment的内存泄露比这个要复杂一些。
android系统为了提高message的复用，使用到了一个message池来管理那些被回收的message对象，可以通过Message的obtain方法从message池中获取到message，而message最终会被放到messagequeue中等待被处理，源码如下
for (;;) {
Message msg = queue.next(); // might block
if (msg == null) {
// No message indicates that the message queue is quitting.
return;
}
...
msg.recycleUnchecked();
}
通过next获取到message对象，最终执行完毕后通过recycleUnchecked被回收回message池中，然后继续next取出下一个要被处理的message对象，如果没有要被执行的message则next会被一直阻塞在这里。由于msg是一个局部变量，next被阻塞住会导致该局部变量无法被回收，但是最为关键的一点是，这个msg对象却被放到了message池中，可被其他的线程使用到。这就会导致一旦该msg对象被其他线程使用到就可能导致msg成员变量一直持有某些引用对象最终引发内存泄露问题。
而dialogfragment正好就踩到了这个雷上，来看下源码实现
public void setOnDismissListener(@Nullable OnDismissListener listener) {
if (mCancelAndDismissTaken != null) {
throw new IllegalStateException(
"OnDismissListener is already taken by "
+ mCancelAndDismissTaken + " and can not be replaced.");
}
if (listener != null) {
mDismissMessage = mListenersHandler.obtainMessage(DISMISS, listener);
} else {
mDismissMessage = null;
}
}
obtainMessage从message池中获取到了一个message，并且到message的what对象被设置为了listener，listener对象实际上就是一个dialogfragment对象，而dialogfragment又和activity有着关联。到此内存泄露的问题正好触发。知道原因后解决起来心里就有数了，处理方式如下：
private static class DialogDismissListener extends WeakReference implements DialogInterface.OnDismissListener {
private DialogDismissListener(FixDialogFragment referent) {
super(referent);
}
@Override
public void onDismiss(DialogInterface dialog) {
FixDialogFragment dialogFragment = get();
if (dialogFragment != null) {
dialogFragment.onDismissDialog(dialog);
}
}
}
将message的what对象最终指向一个弱引用对象
mDialog.setOnDismissListener(new DialogDismissListener(this));
同理CancelListener处理过程类似。上述解决方法需要修改dialogfragment源码进行解决.
3 加载含有fragment的view导致的崩溃
这又是一个和fragment相关的坑。我们的dialogfragment所展示的view是通过解析xml来获取到的，一般而言这个xml中都是一些普通的view控件，但如果xml中包含了fragment节点那么问题就会稍微复杂一些。
自己在开发中经常遇到这种通过recyclerview来展示item的场景，无论是刷新操作还是加载更多都离不开那些通用的逻辑处理，所以封装了一个fragment，给出需要展示的数据后该fragment就会自动帮你展示出来，避免了一些重复的逻辑判断工作。其实google也封装了一个类似的fragment叫ListFragment。
所以基于上述情况，我在dialogfragment需要展示的xml上使用了该fragment，导致的结果就是多次展示dialogfragment后引起了app崩溃问题。崩溃信息类似如下
Caused by: java.lang.IllegalArgumentException: Binary XML file line #30: Duplicate id 0x7f080047
造成这个问题的主要原因就是当dialogfragment被展示时，实际上总共生成了两个fragment，而且都被添加到了同一个fragmentmanager之上，但是在remove的时候却只移除了其中一个，导致再次展示dialogfragment时出现重复添加的异常。
这两个fragment其中一个就是dialogfragment，而另一个就是xml中自己设置的fragment。dialogfragment本质上就是一个fragment，这个看类结构就明白
public class DialogFragment extends Fragment implements OnCancelListener, OnDismissListener
dialogfragment的show源码如下
public void show(FragmentManager manager, String tag) {
this.mDismissed = false;
this.mShownByMe = true;
FragmentTransaction ft = manager.beginTransaction();
ft.add(this, tag);
ft.commit();
}
manager对象就是通过Activity获取到的，当dialogfragment去解析xml时如果内部有fragment，也会将该fragment添加到该fragmentmanager上，但是看下dialogfragment的dismiss源码
void dismissInternal(boolean allowStateLoss) {
if (!this.mDismissed) {
this.mDismissed = true;
this.mShownByMe = false;
if (this.mDialog != null) {
this.mDialog.dismiss();
}
this.mViewDestroyed = true;
if (this.mBackStackId >= 0) {
this.getFragmentManager().popBackStack(this.mBackStackId, 1);
this.mBackStackId = -1;
} else {
FragmentTransaction ft = this.getFragmentManager().beginTransaction();
ft.remove(this);
if (allowStateLoss) {
ft.commitAllowingStateLoss();
} else {
ft.commit();
}
}
}
}
很明显，它只会remove掉dialogfragment，而xml中的fragment会被一直保留在manager之上。明白崩溃原因之后解决方法也就简单了，在dialogfragment被dismiss的时候remove掉那个xml中的fragment即可，dialogfragment提供了dismiss的监听，在内部处理逻辑
FragmentActivity context = (FragmentActivity) getContext();
if (context != null) {
FragmentManager manager = context.getSupportFragmentManager();
Fragment fragment = manager.findFragmentById(XXX);
if (fragment != null) {
FragmentTransaction transaction = manager.beginTransaction();
transaction.remove(fragment);
transaction.commitAllowingStateLoss();
}
}
实际上当存在fragment嵌套问题时，一般内部的fragment会被添加到外部fragment的childmanager上，如果是这种情况应该不会存在上述dialogfragment崩溃的问题，可以看下fragment内部源码的处理，最终会调用到如下方法
public LayoutInflater getLayoutInflater(@Nullable Bundle savedFragmentState) {
if (this.mHost == null) {
throw new IllegalStateException("onGetLayoutInflater() cannot be executed until the Fragment is attached to the FragmentManager.");
} else {
LayoutInflater result = this.mHost.onGetLayoutInflater();
this.getChildFragmentManager();
LayoutInflaterCompat.setFactory2(result, this.mChildFragmentManager.getLayoutInflaterFactory());
return result;
}
}
getChildFragmentManager会生成一个childmanager供内部fragment'使用，但是dialogfragment却复写了onGetLayoutInflater方法
@NonNull
public LayoutInflater onGetLayoutInflater(@Nullable Bundle savedInstanceState) {
if (!this.mShowsDialog) {
return super.onGetLayoutInflater(savedInstanceState);
} else {
this.mDialog = this.onCreateDialog(savedInstanceState);
if (this.mDialog != null) {
this.setupDialog(this.mDialog, this.mStyle);
return (LayoutInflater)this.mDialog.getContext().getSystemService("layout_inflater");
} else {
return (LayoutInflater)this.mHost.getContext().getSystemService("layout_inflater");
}
}
}
文章到此就分析完了自己在开发过程中遇到的几个关于dialogfragment问题，最后给出解决后的代码，以下代码是直接在dialogfragment的基础上进行修改的，直接拷贝出dialogfragment源码修改即可。完整的源码如下，看着很多但实际上绝大部分都是dialogfragment本身的源码，具体的改动点在上述文章都已经说明不在重复讲述
/**
* 解决内存泄露，弹框可能引起的崩溃问题
* @author stupid pig mandy
* */
public class FixDialogFragment extends Fragment
implements DialogInterface.OnCancelListener, DialogInterface.OnDismissListener {
/** @hide */
@RestrictTo(LIBRARY_GROUP)
@IntDef({STYLE_NORMAL, STYLE_NO_TITLE, STYLE_NO_FRAME, STYLE_NO_INPUT})
@Retention(RetentionPolicy.SOURCE)
private @interface DialogStyle {}
/**
* Style for {@link #setStyle(int, int)}: a basic,
* normal dialog.
*/
public static final int STYLE_NORMAL = 0;
/**
* Style for {@link #setStyle(int, int)}: don't include
* a title area.
*/
public static final int STYLE_NO_TITLE = 1;
/**
* Style for {@link #setStyle(int, int)}: don't draw
* any frame at all; the view hierarchy returned by {@link #onCreateView}
* is entirely responsible for drawing the dialog.
*/
public static final int STYLE_NO_FRAME = 2;
/**
* Style for {@link #setStyle(int, int)}: like
* {@link #STYLE_NO_FRAME}, but also disables all input to the dialog.
* The user can not touch it, and its window will not receive input focus.
*/
public static final int STYLE_NO_INPUT = 3;
private static final String SAVED_DIALOG_STATE_TAG = "android:savedDialogState";
private static final String SAVED_STYLE = "android:style";
private static final String SAVED_THEME = "android:theme";
private static final String SAVED_CANCELABLE = "android:cancelable";
private static final String SAVED_SHOWS_DIALOG = "android:showsDialog";
private static final String SAVED_BACK_STACK_ID = "android:backStackId";
int mStyle = STYLE_NORMAL;
int mTheme = 0;
boolean mCancelable = true;
boolean mShowsDialog = true;
int mBackStackId = -1;
Dialog mDialog;
boolean mViewDestroyed;
boolean mDismissed;
boolean mShownByMe;
public FixDialogFragment() {
}
/**
* Call to customize the basic appearance and behavior of the
* fragment's dialog. This can be used for some common dialog behaviors,
* taking care of selecting flags, theme, and other options for you. The
* same effect can be achieve by manually setting Dialog and Window
* attributes yourself. Calling this after the fragment's Dialog is
* created will have no effect.
*
* @param style Selects a standard style: may be {@link #STYLE_NORMAL},
* {@link #STYLE_NO_TITLE}, {@link #STYLE_NO_FRAME}, or
* {@link #STYLE_NO_INPUT}.
* @param theme Optional custom theme. If 0, an appropriate theme (based
* on the style) will be selected for you.
*/
public void setStyle(@DialogStyle int style, @StyleRes int theme) {
mStyle = style;
if (mStyle == STYLE_NO_FRAME || mStyle == STYLE_NO_INPUT) {
mTheme = android.R.style.Theme_Panel;
}
if (theme != 0) {
mTheme = theme;
}
}
/**
* Display the dialog, adding the fragment to the given FragmentManager. This
* is a convenience for explicitly creating a transaction, adding the
* fragment to it with the given tag, and {@link FragmentTransaction#commit() committing} it.
* This does not add the transaction to the fragment back stack. When the fragment
* is dismissed, a new transaction will be executed to remove it from
* the activity.
* @param manager The FragmentManager this fragment will be added to.
* @param tag The tag for this fragment, as per
* {@link FragmentTransaction#add(Fragment, String) FragmentTransaction.add}.
*/
public void show(FragmentManager manager, String tag) {
mDismissed = false;
mShownByMe = true;
FragmentTransaction ft = manager.beginTransaction();
ft.add(this, tag);
ft.commitAllowingStateLoss();
}
/**
* Display the dialog, adding the fragment using an existing transaction
* and then {@link FragmentTransaction#commit() committing} the transaction.
* @param transaction An existing transaction in which to add the fragment.
* @param tag The tag for this fragment, as per
* {@link FragmentTransaction#add(Fragment, String) FragmentTransaction.add}.
* @return Returns the identifier of the committed transaction, as per
* {@link FragmentTransaction#commit() FragmentTransaction.commit()}.
*/
public int show(FragmentTransaction transaction, String tag) {
mDismissed = false;
mShownByMe = true;
transaction.add(this, tag);
mViewDestroyed = false;
mBackStackId = transaction.commit();
return mBackStackId;
}
/**
* Display the dialog, immediately adding the fragment to the given FragmentManager. This
* is a convenience for explicitly creating a transaction, adding the
* fragment to it with the given tag, and calling {@link FragmentTransaction#commitNow()}.
* This does not add the transaction to the fragment back stack. When the fragment
* is dismissed, a new transaction will be executed to remove it from
* the activity.
* @param manager The FragmentManager this fragment will be added to.
* @param tag The tag for this fragment, as per
* {@link FragmentTransaction#add(Fragment, String) FragmentTransaction.add}.
*/
public void showNow(FragmentManager manager, String tag) {
mDismissed = false;
mShownByMe = true;
FragmentTransaction ft = manager.beginTransaction();
ft.add(this, tag);
ft.commitNow();
}
/**
* Dismiss the fragment and its dialog. If the fragment was added to the
* back stack, all back stack state up to and including this entry will
* be popped. Otherwise, a new transaction will be committed to remove
* the fragment.
*/
public void dismiss() {
dismissInternal(false);
}
/**
* Version of {@link #dismiss()} that uses
* {@link FragmentTransaction#commitAllowingStateLoss()
* FragmentTransaction.commitAllowingStateLoss()}. See linked
* documentation for further details.
*/
public void dismissAllowingStateLoss() {
dismissInternal(true);
}
void dismissInternal(boolean allowStateLoss) {
if (mDismissed) {
return;
}
mDismissed = true;
mShownByMe = false;
if (mDialog != null) {
mDialog.dismiss();
}
mViewDestroyed = true;
if (mBackStackId >= 0) {
getFragmentManager().popBackStack(mBackStackId,
FragmentManager.POP_BACK_STACK_INCLUSIVE);
mBackStackId = -1;
} else {
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.remove(this);
if (allowStateLoss) {
ft.commitAllowingStateLoss();
} else {
ft.commit();
}
}
}
public Dialog getDialog() {
return mDialog;
}
@StyleRes
public int getTheme() {
return mTheme;
}
/**
* Control whether the shown Dialog is cancelable. Use this instead of
* directly calling {@link Dialog#setCancelable(boolean)
* Dialog.setCancelable(boolean)}, because DialogFragment needs to change
* its behavior based on this.
*
* @param cancelable If true, the dialog is cancelable. The default
* is true.
*/
public void setCancelable(boolean cancelable) {
mCancelable = cancelable;
if (mDialog != null) mDialog.setCancelable(cancelable);
}
/**
* Return the current value of {@link #setCancelable(boolean)}.
*/
public boolean isCancelable() {
return mCancelable;
}
/**
* Controls whether this fragment should be shown in a dialog. If not
* set, no Dialog will be created in {@link #onActivityCreated(Bundle)},
* and the fragment's view hierarchy will thus not be added to it. This
* allows you to instead use it as a normal fragment (embedded inside of
* its activity).
*
* This is normally set for you based on whether the fragment is
* associated with a container view ID passed to
* {@link FragmentTransaction#add(int, Fragment) FragmentTransaction.add(int, Fragment)}.
* If the fragment was added with a container, setShowsDialog will be
* initialized to false; otherwise, it will be true.
*
* @param showsDialog If true, the fragment will be displayed in a Dialog.
* If false, no Dialog will be created and the fragment's view hierarchy
* left undisturbed.
*/
public void setShowsDialog(boolean showsDialog) {
mShowsDialog = showsDialog;
}
/**
* Return the current value of {@link #setShowsDialog(boolean)}.
*/
public boolean getShowsDialog() {
return mShowsDialog;
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (!mShownByMe) {
// If not explicitly shown through our API, take this as an
// indication that the dialog is no longer dismissed.
mDismissed = false;
}
}
@Override
public void onDetach() {
super.onDetach();
if (!mShownByMe && !mDismissed) {
// The fragment was not shown by a direct call here, it is not
// dismissed, and now it is being detached... well, okay, thou
// art now dismissed. Have fun.
mDismissed = true;
}
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mShowsDialog = mContainerId == 0;
if (savedInstanceState != null) {
mStyle = savedInstanceState.getInt(SAVED_STYLE, STYLE_NORMAL);
mTheme = savedInstanceState.getInt(SAVED_THEME, 0);
mCancelable = savedInstanceState.getBoolean(SAVED_CANCELABLE, true);
mShowsDialog = savedInstanceState.getBoolean(SAVED_SHOWS_DIALOG, mShowsDialog);
mBackStackId = savedInstanceState.getInt(SAVED_BACK_STACK_ID, -1);
}
}
@Override
public LayoutInflater onGetLayoutInflater(Bundle savedInstanceState) {
if (!mShowsDialog) {
return super.onGetLayoutInflater(savedInstanceState);
}
mDialog = onCreateDialog(savedInstanceState);
if (mDialog != null) {
setupDialog(mDialog, mStyle);
return (LayoutInflater) mDialog.getContext().getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
}
return (LayoutInflater) mHost.getContext().getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
}
/** @hide */
@RestrictTo(LIBRARY_GROUP)
public void setupDialog(Dialog dialog, int style) {
switch (style) {
case STYLE_NO_INPUT:
dialog.getWindow().addFlags(
WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE);
// fall through...
case STYLE_NO_FRAME:
case STYLE_NO_TITLE:
dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
}
}
/**
* Override to build your own custom Dialog container. This is typically
* used to show an AlertDialog instead of a generic Dialog; when doing so,
* {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)} does not need
* to be implemented since the AlertDialog takes care of its own content.
*
*
This method will be called after {@link #onCreate(Bundle)} and
* before {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}. The
* default implementation simply instantiates and returns a {@link Dialog}
* class.
*
*
Note: DialogFragment own the {@link Dialog#setOnCancelListener
* Dialog.setOnCancelListener} and {@link Dialog#setOnDismissListener
* Dialog.setOnDismissListener} callbacks. You must not set them yourself.
* To find out about these events, override {@link #onCancel(DialogInterface)}
* and {@link #onDismiss(DialogInterface)}.
*
* @param savedInstanceState The last saved instance state of the Fragment,
* or null if this is a freshly created Fragment.
*
* @return Return a new Dialog instance to be displayed by the Fragment.
*/
@NonNull
public Dialog onCreateDialog(Bundle savedInstanceState) {
return new Dialog(getActivity(), getTheme());
}
@Override
public void onCancel(DialogInterface dialog) {
}
@Override
public void onDismiss(DialogInterface dialog) {
if (!mViewDestroyed) {
// Note: we need to use allowStateLoss, because the dialog
// dispatches this asynchronously so we can receive the call
// after the activity is paused. Worst case, when the user comes
// back to the activity they see the dialog again.
dismissInternal(true);
}
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
if (!mShowsDialog) {
return;
}
View view = getView();
if (view != null) {
if (view.getParent() != null) {
throw new IllegalStateException(
"DialogFragment can not be attached to a container view");
}
mDialog.setContentView(view);
}
final Activity activity = getActivity();
if (activity != null) {
mDialog.setOwnerActivity(activity);
}
mDialog.setCancelable(mCancelable);
mDialog.setOnCancelListener(new DialogCancelListener(this));
mDialog.setOnDismissListener(new DialogDismissListener(this));
if (savedInstanceState != null) {
Bundle dialogState = savedInstanceState.getBundle(SAVED_DIALOG_STATE_TAG);
if (dialogState != null) {
mDialog.onRestoreInstanceState(dialogState);
}
}
}
@Override
public void onStart() {
super.onStart();
if (mDialog != null) {
mViewDestroyed = false;
mDialog.show();
}
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
if (mDialog != null) {
Bundle dialogState = mDialog.onSaveInstanceState();
if (dialogState != null) {
outState.putBundle(SAVED_DIALOG_STATE_TAG, dialogState);
}
}
if (mStyle != STYLE_NORMAL) {
outState.putInt(SAVED_STYLE, mStyle);
}
if (mTheme != 0) {
outState.putInt(SAVED_THEME, mTheme);
}
if (!mCancelable) {
outState.putBoolean(SAVED_CANCELABLE, mCancelable);
}
if (!mShowsDialog) {
outState.putBoolean(SAVED_SHOWS_DIALOG, mShowsDialog);
}
if (mBackStackId != -1) {
outState.putInt(SAVED_BACK_STACK_ID, mBackStackId);
}
}
@CallSuper
protected void onDismissDialog(DialogInterface dialog) {
onDismiss(dialog);
}
protected void onCancelDialog(DialogInterface dialog) {
}
@Override
public void onStop() {
super.onStop();
if (mDialog != null) {
mDialog.hide();
}
}
/**
* Remove dialog.
*/
@Override
public void onDestroyView() {
super.onDestroyView();
if (mDialog != null) {
// Set removed here because this dismissal is just to hide
// the dialog -- we don't want this to cause the fragment to
// actually be removed.
mViewDestroyed = true;
mDialog.dismiss();
mDialog = null;
}
}
private static class DialogDismissListener extends WeakReference implements DialogInterface.OnDismissListener {
private DialogDismissListener(FixDialogFragment referent) {
super(referent);
}
@Override
public void onDismiss(DialogInterface dialog) {
FixDialogFragment dialogFragment = get();
if (dialogFragment != null) {
dialogFragment.onDismissDialog(dialog);
}
}
}
private static class DialogCancelListener extends WeakReference implements DialogInterface.OnCancelListener {
private DialogCancelListener(FixDialogFragment referent) {
super(referent);
}
@Override
public void onCancel(DialogInterface dialog) {
FixDialogFragment dialogFragment = get();
if (dialogFragment != null) {
dialogFragment.onCancelDialog(dialog);
}
}
}
}