前言

上一节我们讲解了在Android平台如何通过MvvmCross实现启动界面，以及如何处理启动时的白屏问题。

这一节我们讲解一下如何在Android平台使用Fragment。

Fragment 应用

什么是Fragment

Fragment是Android开发常用的一种组件。通过Fragment的使用可以降低内存的使用，增加App的流畅度。已经有很多大神讲解过Fragment的内容了，请看。

MvvmCross中与Fragment相关的对象

在MvvmCross中，已经实现了很多与Fragment相关的对象，极大的方便我们的使用。

首先我们需要通过nuget 添加MvvmCross对Fragment的支持库 。现在我们来看一下MvvmCross为我们实现了哪些相关的对象。

这里我们会使用以下几个MvvmCross定义的几个对象：

• MvxFragment： Fragment对象的基类，所有基于MvvvmCross实现的Fragment都需要从此对象继承。

namespace MvvmCross.Droid.FullFragging.Fragments{    [Register("mvvmcross.droid.fullfragging.fragments.MvxFragment")]    public class MvxFragment : MvxEventSourceFragment, IMvxFragmentView, IMvxBindingContextOwner, IMvxView, IMvxDataConsumer    {        protected MvxFragment();        protected MvxFragment(IntPtr javaReference, JniHandleOwnership transfer);        public IMvxBindingContext BindingContext { get; set; }        public object DataContext { get; set; }        public string UniqueImmutableCacheTag { get; }        public virtual IMvxViewModel ViewModel { get; set; }        public static MvxFragment NewInstance(Bundle bundle);        public virtual void OnViewModelSet();    }}

• MvxFragmentAttribute，Fragment特性标签，标识了当前Fragment的嵌入的宿主以及显示时后些参数

namespace MvvmCross.Droid.Shared.Attributes{    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]    public class MvxFragmentAttribute : Attribute    {        public MvxFragmentAttribute(Type parentActivityViewModelType, int fragmentContentId, bool addToBackStack = false);        public bool AddToBackStack { get; set; }        public int FragmentContentId { get; }        public bool IsCacheableFragment { get; set; }        public Type ParentActivityViewModelType { get; }        public Type ViewModelType { get; set; }    }}

• MvxCachingFragmentActivity：Fragment的宿主窗口

namespace MvvmCross.Droid.FullFragging.Caching{    [Register("mvvmcross.droid.fullfragging.caching.MvxCachingFragmentActivity")]    public class MvxCachingFragmentActivity : MvxActivity, IFragmentCacheableActivity, IMvxFragmentHost    {        public const string ViewModelRequestBundleKey = "__mvxViewModelRequest";        protected MvxCachingFragmentActivity();        protected MvxCachingFragmentActivity(IntPtr javaReference, JniHandleOwnership transfer);        public IFragmentCacheConfiguration FragmentCacheConfiguration { get; }        public virtual IFragmentCacheConfiguration BuildFragmentCacheConfiguration();        public virtual bool Close(IMvxViewModel viewModel);        public override void OnBackPressed();        public virtual void OnBeforeFragmentChanging(IMvxCachedFragmentInfo fragmentInfo, FragmentTransaction transaction);        public virtual void OnFragmentChanged(IMvxCachedFragmentInfo fragmentInfo);        public virtual void OnFragmentChanging(IMvxCachedFragmentInfo fragmentInfo, FragmentTransaction transaction);        public virtual void OnFragmentCreated(IMvxCachedFragmentInfo fragmentInfo, FragmentTransaction transaction);        public virtual void OnFragmentPopped(IList
      
        currentFragmentsInfo);        public virtual bool Show(MvxViewModelRequest request, Bundle bundle, Type fragmentType, MvxFragmentAttribute fragmentAttribute);        protected virtual void CloseFragment(string tag, int contentId);        protected virtual string FragmentJavaName(Type fragmentType);        protected virtual IEnumerable
       
         GetCurrentCacheableFragments();        protected virtual List
        
          GetCurrentCacheableFragmentsInfo();        protected IMvxCachedFragmentInfo GetFragmentInfoByTag(string tag);        protected virtual string GetFragmentTag(MvxViewModelRequest request, Bundle bundle, Type fragmentType);        protected virtual IMvxCachedFragmentInfo GetLastFragmentInfo();        protected virtual string GetTagFromFragment(Fragment fragment);        protected override void OnCreate(Bundle bundle);        protected override void OnPostCreate(Bundle savedInstanceState);        protected override void OnSaveInstanceState(Bundle outState);        protected virtual void ReplaceFragment(FragmentTransaction ft, IMvxCachedFragmentInfo fragInfo);        protected virtual FragmentReplaceMode ShouldReplaceCurrentFragment(IMvxCachedFragmentInfo newFragment, IMvxCachedFragmentInfo currentFragment, Bundle replacementBundle);        protected virtual void ShowFragment(string tag, int contentId, Bundle bundle, bool forceAddToBackStack = false, bool forceReplaceFragment = false);        protected enum FragmentReplaceMode        {            NoReplace = 0,            ReplaceFragment = 1,            ReplaceFragmentAndViewModel = 2        }    }}
        
       
      

• MvxFragmentsPresenter，实对Fragment对象的显示，内部对象，MvvmCross框架将自动调用

namespace MvvmCross.Droid.Shared.Presenter{    public class MvxFragmentsPresenter : MvxAndroidViewPresenter    {        public const string ViewModelRequestBundleKey = "__mvxViewModelRequest";        protected FragmentHostRegistrationSettings _fragmentHostRegistrationSettings;        protected Lazy
      
        _lazyNavigationSerializerFactory;        public MvxFragmentsPresenter(IEnumerable
       
         AndroidViewAssemblies);        protected IMvxNavigationSerializer Serializer { get; }        public sealed override void Close(IMvxViewModel viewModel);        public sealed override void Show(MvxViewModelRequest request);        public void Show(MvxViewModelRequest request, MvxViewModelRequest fragmentRequest);        protected virtual void CloseActivity(IMvxViewModel viewModel);        protected virtual void CloseFragment(IMvxViewModel viewModel);        protected IMvxFragmentHost GetActualFragmentHost();        protected virtual void ShowActivity(MvxViewModelRequest request, MvxViewModelRequest fragmentRequest = null);        protected virtual void ShowFragment(MvxViewModelRequest request);    }}
       
      

仿微信的首页来一发

好了，对MvvmCross对Fragment的支持对象我们已经介绍完毕，下面我就动手做一个Fragment的示例，我们就仿照微信的主窗口来试一下

• 首先，定义好宿主，我们用上一节使用的Sample，修改一下主窗口的布局，下部为四个导航按钮，其余部分为当前功能模块的显示窗口，功能模块通过Fragment方式进行展示

using Android.App;using Android.OS;using Android.Widget;using MvvmCross.Droid.Views;using MvxSample.ViewModels;namespace MvxSample.Droid.Views{    [Activity(Label = "MainView", MainLauncher = false, Theme ="@android:style/Theme.Light.NoTitleBar")]    public class MainView : MvvmCross.Droid.FullFragging.Caching.MvxCachingFragmentActivity
      
           {        protected override void OnCreate(Bundle savedInstanceState)        {            base.OnCreate(savedInstanceState);            SetContentView(Resource.Layout.MainPage);            var grp = FindViewById
       
        (Resource.Id.main_rg_toolbar);            grp.CheckedChange += (s, e) =>            {                var btn = FindViewById
        
         (e.CheckedId);                if (btn.Checked == false) return;                if (e.CheckedId == Resource.Id.main_rb_chat)                {                    ViewModel.ShowChat();                }                else if (e.CheckedId == Resource.Id.main_rb_friends)                {                    ViewModel.ShowFriends();                }                else if (e.CheckedId == Resource.Id.main_rb_extras)                {                    ViewModel.ShowExtras();                }                else if (e.CheckedId == Resource.Id.main_rb_my)                {                    ViewModel.ShowMy();                }            };            ViewModel.ShowChat();        }    }}
        
       
      

• 下来，我们定义好要展示的Fragment及布局

namespace MvxSample.Droid.Views{    [MvxFragment(typeof(MainViewModel), Resource.Id.main_container)]    [Register("mvxsample.droid.views.ChatFragment")]    public class ChatFragment: MvxFragment
      
           {        public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)        {            var ignore = base.OnCreateView(inflater, container, savedInstanceState);            var view = this.BindingInflate(Resource.Layout.ChatFragment, container, false);            return view;        }    }}
      

按照定义好的ChatFragment，我们定义其它的几个Fragment，分别为FriendsFragment、ExtrasFragment、MyFragment。

• 在Setup重载方法 CreateViewPresenter:

namespace MvxSample.Droid{    public class Setup : MvxAndroidSetup    {        public Setup(Context applicationContext) : base(applicationContext)        {        }        protected override IMvxApplication CreateApp()        {            return new App();        }        protected override IMvxAndroidViewPresenter CreateViewPresenter()        {            var mvxFragmentsPresenter = new MvxFragmentsPresenter(AndroidViewAssemblies);            Mvx.RegisterSingleton
      
       (mvxFragmentsPresenter);            return mvxFragmentsPresenter;        }    }}
      

• OK,全部代码就完成了，我们运行一下看看效果吧

我们可以看到，根据选中的导航项不时，会展示不同的Fragment的内容。

小结

这一节我们讲解了Framgent在MvvmCross的应用。包括宿主窗口的定义，Fragment的定义以及如何在Setup中使用MvxFragmentPresenter。

代码奉上: