C# 无法访问外部类型的非静态成员。。。通过嵌套类型

为什么会出现这个错误

错误CS0038:无法访问外部类型的非静态成员

JsonFeedParserTabs.MainActivity'通过嵌套类型

JsonFeedParserTabs.MainActivity.SampleTabFragment'（CS0038） （JsonFeedParserTabs）

我试图将包含json数据的ListView放在选项卡中

这是我的代码：

using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;
using System.Threading.Tasks;
using System.Net.Http;
using Newtonsoft.Json;
using System.Linq;

namespace JsonFeedParserTabs
{
    [Activity (Label = "Feed Reader", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        ListView listView;
//      ProgressBar progressBar;
        RootObject result;

        string url = "http://javatechig.com/api/get_category_posts/?dev=1&slug=android";

        protected override void OnCreate (Bundle bundle)
        {
            base.OnCreate (bundle);

            // Set our view from the "main" layout resource.
            SetContentView (Resource.Layout.Main);

            this.ActionBar.NavigationMode = ActionBarNavigationMode.Tabs;

            AddTab (" Tab 1", new SampleTabFragment ());
//          AddTab (" Tab 2", new SampleTabFragment2 ());

            if (bundle != null)
                this.ActionBar.SelectTab(this.ActionBar.GetTabAt(bundle.GetInt("tab")));
        }

        protected override void OnSaveInstanceState(Bundle outState)
        {
            outState.PutInt("tab", this.ActionBar.SelectedNavigationIndex);

            base.OnSaveInstanceState(outState);
        }

        void AddTab (string tabText, Fragment view)
        {
            var tab = this.ActionBar.NewTab ();

            tab.SetText (tabText);

            // Must set event handler before adding tab.
            tab.TabSelected += delegate(object sender, ActionBar.TabEventArgs e) {
                var fragment = this.FragmentManager.FindFragmentById(Resource.Id.fragmentContainer);

                if (fragment != null)
                    e.FragmentTransaction.Remove(fragment);

                e.FragmentTransaction.Add (Resource.Id.fragmentContainer, view);
            };
            tab.TabUnselected += delegate(object sender, ActionBar.TabEventArgs e) {
                e.FragmentTransaction.Remove(view);
            };

            this.ActionBar.AddTab (tab);
        }

        class SampleTabFragment : Fragment
        {
            public override View OnCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
            {
                base.OnCreateView (inflater, container, savedInstanceState);

                var view = inflater.Inflate (Resource.Layout.Tab, container, false);

                // Initializing listView.
                listView = view.FindViewById<ListView> (Resource.Id.listView); // <-- Error!
                listView.ItemClick += OnListItemClick; // <-- Error!

//              progressBar = view.FindViewById<ProgressBar> (Resource.Id.progressBar);
//  
//              // Showing loading progressBar.
//              progressBar.Visibility = ViewStates.Visible;

                // Download and display data in url.
                downloadJsonFeedAsync (url); // <-- Error!

                return view;
            }
        }

//      class SampleTabFragment2 : Fragment
//      {
//          public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
//          {
//              base.OnCreateView(inflater, container, savedInstanceState);
//
//              var view = inflater.Inflate(Resource.Layout.Tab, container, false);
//              var sampleTextView = view.FindViewById<TextView>(Resource.Id.sampleTextView);
//
//              sampleTextView.Text = "Sample fragment text 2.";
//
//              return view;
//          }
//      }

        public async void downloadJsonFeedAsync(String url)
        {
            var httpClient = new HttpClient();
            Task<string> contentsTask = httpClient.GetStringAsync(url);

            // Await! control returns to the caller and the task continues to run on another thread.
            string content = await contentsTask;
            Console.Out.WriteLine("Response Body: \r\n {0}", content);

            // Convert string to JSON object.
            result = Newtonsoft.Json.JsonConvert.DeserializeObject<RootObject> (content);

            // Update listview.
            RunOnUiThread (() => {
                listView.Adapter = new CustomListAdapter(this, result.posts);
//              progressBar.Visibility = ViewStates.Gone;
            });
        }

        void OnListItemClick(object sender, AdapterView.ItemClickEventArgs e)
        {
            Post item = result.posts.ElementAt (e.Position);

            // Passing object form one activity to other.
            Intent i = new Intent(Application.Context, typeof(FeedDetailsActivity));
            i.PutExtra("item", JsonConvert.SerializeObject(item));
            StartActivity(i);
        }
    }
}

使用系统；
使用Android.App；
使用Android.Content；
使用Android.Runtime；
使用Android.Views；
使用Android.Widget；
使用Android.OS；
使用System.Threading.Tasks；
使用System.Net.Http；
使用Newtonsoft.Json；
使用System.Linq；
命名空间JsonFeedParserTables
{
[活动（Label=“提要阅读器”，MainLauncher=true，Icon=“@drawable/Icon”）]
公共课活动：活动
{
列表视图列表视图；
//ProgressBar ProgressBar；
根对象结果；
字符串url=”http://javatechig.com/api/get_category_posts/?dev=1&slug=android";
创建时受保护的覆盖无效（捆绑包）
{
base.OnCreate（bundle）；
//从“主”布局资源设置视图。
SetContentView（Resource.Layout.Main）；
this.ActionBar.NavigationMode=ActionBarNavigationMode.Tabs；
AddTab（“tab1”，新的SampleTabFragment（））；
//AddTab（“Tab 2”，新样本tabfragment2（））；
if（bundle！=null）
this.ActionBar.SelectTab（this.ActionBar.gettab（bundle.GetInt（“tab”））；
}
受保护的覆盖无效OnSaveInstanceState（包超出状态）
{
outState.PutInt（“tab”，this.ActionBar.SelectedNavigationIndex）；
base.OnSaveInstanceState（超出状态）；
}
void AddTab（字符串选项卡文本，片段视图）
{
var tab=this.ActionBar.NewTab（）；
tab.SetText（tabText）；
//必须在添加选项卡之前设置事件处理程序。
tab.TabSelected+=委托（对象发送者，ActionBar.TabEventArgs e）{
var fragment=this.FragmentManager.FindFragmentById（Resource.Id.fragmentContainer）；
if（片段！=null）
e、 碎片事务。删除（碎片）；
e、 FragmentTransaction.Add（Resource.Id.fragmentContainer，视图）；
};
tab.TabUnselected+=委托（对象发送者，ActionBar.TabEventArgs e）{
e、 碎片事务。删除（视图）；
};
this.ActionBar.AddTab（tab）；
}
类SampleTabFragment:Fragment
{
创建视图上的公共覆盖视图（布局、充气机、视图组容器、捆绑包保存状态）
{
base.OnCreateView（充气机、容器、保存状态）；
var视图=充气机。充气（Resource.Layout.Tab，container，false）；
//正在初始化listView。
listView=view.FindViewById（Resource.Id.listView）；//它准确地告诉您它不能做什么。无法从
MainActivity
类型中声明的片段类型访问
MainActivity
成员。因此，当您尝试调用
downloadJsonFeedAsync（url）；
时，它会失败，因为它不是静态（类）方法。片段（尽管在类型中声明）不存在于
MainActivity
类型的实例中

除非有令人信服的理由让它们保留在MainActivity类型中，否则我会将它们移出。它们还应该有一个对MainActivity类型的引用，这样您就可以对其调用
downloadJsonFeedAsync（string）

另一方面（我很欣赏这是一篇非常不请自来的评论：）你可能想考虑使用一个MVVM模式。看起来你正在混合演示、应用程序控制和业务数据。如果这个应用程序超过一两页，你会发现隔离职责有很大的和平。
它会非常有帮助。你告诉我们到底是哪一行造成了错误。ment

class？我想这实际上是一个循环引用。listView是MainActivity中的一个私有字段；SampleTabFragment（一个单独的嵌套类）无法访问it@Jason这是带有“错误！”注释的三行文字。好的，谢谢你的帮助和提示。今天有机会我会调查的。：）

using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;
using System.Threading.Tasks;
using System.Net.Http;
using Newtonsoft.Json;
using System.Linq;

namespace JsonFeedParserTabs
{
    [Activity (Label = "Feed Reader", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        ListView listView;
//      ProgressBar progressBar;
        RootObject result;

        string url = "http://javatechig.com/api/get_category_posts/?dev=1&slug=android";

        protected override void OnCreate (Bundle bundle)
        {
            base.OnCreate (bundle);

            // Set our view from the "main" layout resource.
            SetContentView (Resource.Layout.Main);

            this.ActionBar.NavigationMode = ActionBarNavigationMode.Tabs;

            AddTab (" Tab 1", new SampleTabFragment (this));
//          AddTab (" Tab 2", new SampleTabFragment2 ());

            if (bundle != null)
                this.ActionBar.SelectTab(this.ActionBar.GetTabAt(bundle.GetInt("tab")));
        }

        protected override void OnSaveInstanceState(Bundle outState)
        {
            outState.PutInt("tab", this.ActionBar.SelectedNavigationIndex);

            base.OnSaveInstanceState(outState);
        }

        void AddTab (string tabText, Fragment view)
        {
            var tab = this.ActionBar.NewTab ();

            tab.SetText (tabText);

            // Must set event handler before adding tab.
            tab.TabSelected += delegate(object sender, ActionBar.TabEventArgs e) {
                var fragment = this.FragmentManager.FindFragmentById(Resource.Id.fragmentContainer);

                if (fragment != null)
                    e.FragmentTransaction.Remove(fragment);

                e.FragmentTransaction.Add (Resource.Id.fragmentContainer, view);
            };
            tab.TabUnselected += delegate(object sender, ActionBar.TabEventArgs e) {
                e.FragmentTransaction.Remove(view);
            };

            this.ActionBar.AddTab (tab);
        }

        class SampleTabFragment : Fragment
        {
            private MainActivity context;
            public SampleTabFragment(MainActivity _context) : base()
            {
                this.context = _context;
            }

            public override View OnCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
            {
                base.OnCreateView (inflater, container, savedInstanceState);

                var view = inflater.Inflate (Resource.Layout.Tab, container, false);

                // Initializing listView.
                context.listView = view.FindViewById<ListView> (Resource.Id.listView);
                context.listView.ItemClick += context.OnListItemClick;

//              progressBar = view.FindViewById<ProgressBar> (Resource.Id.progressBar);
//  
//              // Showing loading progressBar.
//              progressBar.Visibility = ViewStates.Visible;

                // Download and display data in url.
                context.downloadJsonFeedAsync (context.url);

                return view;
            }
        }

//      class SampleTabFragment2 : Fragment
//      {
//          public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
//          {
//              base.OnCreateView(inflater, container, savedInstanceState);
//
//              var view = inflater.Inflate(Resource.Layout.Tab, container, false);
//              var sampleTextView = view.FindViewById<TextView>(Resource.Id.sampleTextView);
//
//              sampleTextView.Text = "Sample fragment text 2.";
//
//              return view;
//          }
//      }

        public async void downloadJsonFeedAsync(String url)
        {
            var httpClient = new HttpClient();
            Task<string> contentsTask = httpClient.GetStringAsync(url);

            // Await! control returns to the caller and the task continues to run on another thread.
            string content = await contentsTask;
            Console.Out.WriteLine("Response Body: \r\n {0}", content);

            // Convert string to JSON object.
            result = Newtonsoft.Json.JsonConvert.DeserializeObject<RootObject> (content);

            // Update listview.
            RunOnUiThread (() => {
                listView.Adapter = new CustomListAdapter(this, result.posts);
//              progressBar.Visibility = ViewStates.Gone;
            });
        }

        void OnListItemClick(object sender, AdapterView.ItemClickEventArgs e)
        {
            Post item = result.posts.ElementAt (e.Position);

            // Passing object form one activity to other.
            Intent i = new Intent(Application.Context, typeof(FeedDetailsActivity));
            i.PutExtra("item", JsonConvert.SerializeObject(item));
            StartActivity(i);
        }
    }
}