从从 recyclerview 适配器 (xamarin.android) 启动的另一个片段返回到上一个片段

Question

所以我有一个应用程序如下： 用户输入其凭据的登录页面，如果他的凭据正确，则可以访问主应用程序。如果他选中记住我复选框，他的用户名和密码将保存在共享首选项中，以便他可以在第二次直接进入主应用程序。

主应用程序有一个带有 viewpager 的选项卡式布局。在其中一个选项卡中，它是一个片段，我使用 recyclerview 以行显示从数据库中获取的数据。 现在在每一行中都有一个回复按钮，单击该按钮将显示与每一行对应的详细信息。详细信息将显示在新片段中。

所以关键是我设法在 recyclerview 的适配器中使用此代码将选项卡的片段替换为新片段：

public class recyclerviewAdapter : RecyclerView.Adapter
        {
            // Event handler for item clicks:
            public event EventHandler<int> ItemClick;

            List <summary_request> summary_Requests=new List<summary_request>();
            //Context context;
            public readonly stores_fragment context;

            public recyclerviewAdapter(stores_fragment context, List<summary_request> sum_req)
            {
                this.context = context;
                summary_Requests = sum_req;

            }
            public override RecyclerView.ViewHolder
                   OnCreateViewHolder(ViewGroup parent, int viewType)
            {
                View itemView = LayoutInflater.From(parent.Context).
                            Inflate(Resource.Layout.recycler_view_data, parent, false);

               
                recyclerview_viewholder vh = new recyclerview_viewholder(itemView, OnClick);
                return vh;
            }
            public override void
                  OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
            {
                recyclerview_viewholder vh = holder as recyclerview_viewholder;
                vh.by_user.Text = summary_Requests[position].By;
                vh.warehousename.Text = summary_Requests[position].warehousename;
                vh.project.Text = summary_Requests[position].project;
                vh.operations_note.Text = summary_Requests[position].destination_Note;
                vh.source_Note.Text = summary_Requests[position].source_Note;
                vh.stockType.Text = summary_Requests[position].stockType;
                vh.requestStatus.Text = summary_Requests[position].requestStatus;
                vh.reply.Click += delegate
                {
                    summary_detail_req fragment = new summary_detail_req();
                    var fm = context.FragmentManager.BeginTransaction();
                    fm.Replace(Resource.Id.frameLayout1, fragment);
                    fm.AddToBackStack(null);
                    fm.Commit();
                    int nb = context.FragmentManager.BackStackEntryCount;
                    Toast.MakeText(context.Context, nb.ToString(), ToastLength.Long).Show();

                };

            }

            

            private void Reply_Click(object sender, EventArgs e)
            {
                Toast.MakeText(context.Context, "reply" , ToastLength.Long).Show();
               
            }

            public override int ItemCount
            {
                get { return summary_Requests.Count; }
            }
            // Raise an event when the item-click takes place:
            void OnClick(int position)
            {
                if (ItemClick != null)
                    ItemClick(this, position);
            }
        }

但我的context.FragmentManager.BackStackEntryCount 仍然为零！我不明白。在我的主要活动中，我将此代码用于 backpress 功能：

 stores_fragment.recyclerviewAdapter adapter;
        
        public override void OnBackPressed()
        {

            string userName = pref.GetString("Username", String.Empty);
            string password = pref.GetString("Password", String.Empty);
            if (userName != String.Empty || password != String.Empty && adapter.context.FragmentManager.BackStackEntryCount == 0)
            {

                this.FinishAffinity();
            }
            else
                base.OnBackPressed();
        }

但我没有得到我想要的。这个功能让我脱离了整个应用程序。if 语句的第一部分是因为没有它，当我从主要活动中按下后退按钮时，它会将我带回登录页面，我不希望那样。 我的问题是我应该怎么做来管理我的片段和 backpress 功能？ 提前致谢。

Answer 1

所以关键是我设法使用 recyclerview 的适配器中的这段代码将选项卡的片段替换为新片段

根据你的描述，你想从recyclerview Button.click打开另一个片段，如果是，请看下面的代码：

在OnBindViewHolder

  int  selectedindex;
    // Fill in the contents of the photo card (invoked by the layout manager):
    public override void
        OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
    {
        selectedindex =position;
        PhotoViewHolder vh = holder as PhotoViewHolder;

        // Set the ImageView and TextView in this ViewHolder's CardView 
        // from this position in the photo album:
        vh.Image.SetImageResource(mPhotoAlbum[position].PhotoID);
        vh.Caption.Text = mPhotoAlbum[position].Caption;
        vh.btnreply.Click += Btnreply_Click;
    }

显示详细的活动。 MainActivity 是 recyclerview 的当前活动。

   private void Btnreply_Click(object sender, EventArgs e)
    {
        Showdetailed(selectedindex);
    }
    private void Showdetailed(int position)
    {
        var intent = new Intent();

        intent.SetClass(MainActivity.mac, typeof(DetailsActivity));
        intent.PutExtra("selectedid", position);
        MainActivity.mac.StartActivity(intent);
    }

详细的activity.cs：

 public class DetailsActivity : Activity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);

        // Create your application here
        var index = Intent.Extras.GetInt("selectedid", 0);

        var details = DetailsFragment.NewInstance(index); // Details
        var fragmentTransaction = FragmentManager.BeginTransaction();
        fragmentTransaction.Add(Android.Resource.Id.Content, details);
        fragmentTransaction.Commit();
    }
}

DetailsFragment.cs：

public class DetailsFragment : Fragment
{
    public int ShownPlayId => Arguments.GetInt("selectedid", 0);
    public static DetailsFragment NewInstance(int index)
    {
        var detailsFrag = new DetailsFragment { Arguments = new Bundle() };
        detailsFrag.Arguments.PutInt("selectedid", index);
        return detailsFrag;
    }


    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        // Use this to return your custom view for this Fragment
        // return inflater.Inflate(Resource.Layout.YourFragment, container, false);

        if (container == null)
        {
            // Currently in a layout without a container, so no reason to create our view.
            return null;
        }

        var scroller = new ScrollView(Activity);

        var text = new TextView(Activity);
        var padding = Convert.ToInt32(TypedValue.ApplyDimension(ComplexUnitType.Dip, 4, Activity.Resources.DisplayMetrics));
        text.SetPadding(padding, padding, padding, padding);
        text.TextSize = 24;
        
        Photo photo =PhotoAlbum.mBuiltInPhotos[ShownPlayId];
        text.Text = photo.Caption;

        scroller.AddView(text);

        return scroller;
    }
}

关于实现fragment，大家可以看看：

https://docs.microsoft.com/en-us/samples/xamarin/monodroid-samples/fragmentswalkthrough/