用一些片段導航掙扎了很多，並且在這幾天沒有任何進展。合同失敗 - 片段標籤爲空
我有一個名爲「NewsViewModel」，其中包含屬性NewsItemWraps的ViewModel。這是包裝模型中的新聞列表。這只是在我的視圖中顯示在列表中，我希望用戶能夠選擇一個新聞項目並查看此新聞的詳細信息。
只要用戶只能看到相同的NewsDetail，這個工作就很好。但是，如果您選擇第1項，回到列表中，選擇項目2查看詳細信息，然後再次導航回列表，我收到以下錯誤： 合同失敗 - 片段標籤爲空！片段標籤默認沒有設置，你應該在FragmentTransaction中添加標籤或者在你的Fragment類中重寫UniqueImmutableCacheTag。
public override void OnBackPressed()
{
var currentFragment = SupportFragmentManager.FindFragmentById(Resource.Id.content_frame) as MvxFragment;
if (currentFragment != null && SupportFragmentManager.BackStackEntryCount >= 1)
{
SupportFragmentManager.PopBackStackImmediate(); //<-- This guy tosses the error
return;
}
if (DrawerLayout != null && DrawerLayout.IsDrawerOpen(GravityCompat.Start))
DrawerLayout.CloseDrawers();
else
base.OnBackPressed();
}
我已經試過修改的fragmentInfo標籤時，我的片段添加到堆棧中的OnFragmentCreated，但這並沒有改變任何東西。沒關係，如果我像OnFragmentCreated中那樣將它添加到後臺堆棧中，或者讓'addToBackstack'布爾處理，就像在示例中一樣。它也不關心它是否被緩存。
public override void OnFragmentCreated(IMvxCachedFragmentInfo fragmentInfo, Android.Support.V4.App.FragmentTransaction transaction)
{
// You can do fragment + transaction based configurations here.
// Note that, the cached fragment might be reused in another transaction afterwards.
//Adding the fragment to the stack manually.
if (fragmentInfo.Tag.Contains(typeof(NewsDetailsViewModel).Name))
{
transaction.AddToBackStack(typeof(NewsDetailsViewModel).Name);
}
base.OnFragmentCreated(fragmentInfo, transaction);
var myCustomInfo = fragmentInfo as CustomFragmentInfo; //How the sample handles the backstack in the factory MainActivityFragmentCacheInfoFactory.
}
我喜歡的類型在cacheFactory：
{
typeof (NewsDetailsViewModel).ToString(),
new CustomFragmentInfo(typeof (NewsDetailsViewModel).Name,
typeof (NewsDetailsFragment),
typeof (NewsDetailsViewModel), cacheFragment: false, addToBackstack: true, isRoot:false)
}
物業在NewsViewModel：
private List<NewsItemWrap> _newsItemWraps;
public List<NewsItemWrap> NewsItemWraps
{
get { return _newsItemWraps ?? (_newsItemWraps = new List<NewsItemWrap>()); }
set { _newsItemWraps = value; RaisePropertyChanged(() => NewsItemWraps); }
}
我一直在玩弄和Mvvmcross這裏修改示例：https://github.com/MvvmCross/MvvmCross-AndroidSupport/tree/master/Samples
任何指針和建議將不勝感激
完整的堆棧：
System.InvalidOperationException: Contract failed - Fragment tag is null! Fragment tags are not set by default, you should add tag during FragmentTransaction or override UniqueImmutableCacheTag in your Fragment class.
02-19 09:38:56.795 I/MonoDroid(30813): UNHANDLED EXCEPTION: 02-19 09:38:56.795 I/MonoDroid(30813): System.InvalidOperationException: Contract failed - Fragment tag is null! Fragment tags are not set by default, you should add tag during FragmentTransaction or override UniqueImmutableCacheTag in your Fragment class. 02-19 09:38:56.795 I/MonoDroid(30813): at MvvmCross.Droid.Support.V7.Fragging.Fragments.MvxFragmentExtensions.RegisterFragmentViewToCacheIfNeeded (IMvxFragmentView fragmentView) [0x0005a] in :0 02-19 09:38:56.795 I/MonoDroid(30813): at MvvmCross.Droid.Support.V7.Fragging.Fragments.MvxBindingFragmentAdapter.HandleCreateCalled (System.Object sender, MvvmCross.Platform.Core.MvxValueEventArgs
1 bundleArgs) [0x00024] in <filename unknown>:0 02-19 09:38:56.795 I/MonoDroid(30813): at MvvmCross.Platform.Core.MvxDelegateExtensionMethods.Raise[T] (System.EventHandler1 eventHandler, System.Object sender, MvvmCross.Platform.Core.T value) [0x00000] in V:\Xamarin\MvvmCross\MvvmCross\Platform\Platform\Core\MvxDelegateExtensionMethods.cs:21 02-19 09:38:56.795 I/MonoDroid(30813): at MvvmCross.Droid.Support.V7.Fragging.Fragments.EventSource.MvxEventSourceFragment.OnCreate (Android.OS.Bundle savedInstanceState) [0x00014] in :0 02-19 09:38:56.795 I/MonoDroid(30813): at Android.Support.V4.App.Fragment.n_OnCreate_Landroid_os_Bundle_ (IntPtr jnienv, IntPtr native__this, IntPtr native_savedInstanceState) [0x00011] in :0 02-19 09:38:56.795 I/MonoDroid(30813): at (wrapper dynamic-method) System.Object:136761ed-d521-468a-9257-5d08a4df776b (intptr,intptr,intptr)
我見過這種情況經常發生。這可能是4.0中的一個錯誤。你能回答這個問題嗎？ – Martijn00
當然沒有問題:) – Stupidus