使用NavigationPage時返回按鈕在第一頁

Question

我在Xamarin.Forms應用程序上有一個自定義列表視圖，它具有用於多選的開關控件。現在我遇到了這個問題，我在我的應用的第一頁上獲得了後退按鈕。第一頁上的後退按鈕不需要，因爲它重定向到黑色頁面。我知道它必須使用Navigation.PushAsync做些什麼。但我無法弄清楚需要改變的地方。如果有人能以正確的方式指導我會有幫助。

這裏是SelectMultipleBasePage.cs頁：

using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Linq; 
//using System.Reflection.Emit; 
using System.Text; 
using Xamarin.Forms; 

namespace _____ 
{ 
    public class SelectMultipleBasePage<T> : ContentPage 
    { 
     public class WrappedSelection<T> : INotifyPropertyChanged 
     { 
      public T Item { get; set; } 
      bool isSelected = false; 
      public bool IsSelected 
      { 
       get 
       { 
        return isSelected; 
       } 
       set 
       { 
        if (isSelected != value) 
        { 
         isSelected = value; 
         PropertyChanged(this, new PropertyChangedEventArgs("IsSelected")); 
         //      PropertyChanged (this, new PropertyChangedEventArgs (nameof (IsSelected))); // C# 6 
        } 
       } 
      } 
      public event PropertyChangedEventHandler PropertyChanged = delegate { }; 
     } 
     public class WrappedItemSelectionTemplate : ViewCell 
     { 
      public WrappedItemSelectionTemplate() 
       : base() 
      { 

       Grid objGrid = new Grid(); 
       objGrid.BackgroundColor = Color.Gray; 
       objGrid.RowDefinitions.Add(new RowDefinition 
       { 
        Height = new GridLength(1, GridUnitType.Star) 
       }); 

       objGrid.ColumnDefinitions.Add(new ColumnDefinition 
       { 
        Width = new GridLength(75, GridUnitType.Absolute) 
       }); 
       objGrid.ColumnDefinitions.Add(new ColumnDefinition 
       { 
        Width = new GridLength(1, GridUnitType.Star) 
       }); 
       objGrid.ColumnDefinitions.Add(new ColumnDefinition 
       { 
        Width = GridLength.Auto 
       }); 

       // 
       // Column 1:- 
       Image objImage = new Image(); 
       objImage.BackgroundColor = Color.Green; 
       objImage.SetBinding(Image.SourceProperty, new Binding("Item.Image")); 
       objGrid.Children.Add(objImage, 0, 0); 

       // 
       // Column 2:- 
       StackLayout objStackLayoutCol2 = new StackLayout(); 
       objGrid.Children.Add(objStackLayoutCol2, 1, 0); 

       Label name = new Label() 
       { 
        Text = "Name" 
       }; 
       Label date = new Label() 
       { 
        Text = "Date" 
       }; 
       name.SetBinding(Label.TextProperty, new Binding("Item.Name")); 
       date.SetBinding(Label.TextProperty, new Binding("Item.Date")); 
       objStackLayoutCol2.Children.Add(name); 
       objStackLayoutCol2.Children.Add(date); 

       // 
       // Column 3:- 
       Switch mainSwitch = new Switch(); 
       mainSwitch.SetBinding(Switch.IsToggledProperty, new Binding("IsSelected")); 
       objGrid.Children.Add(mainSwitch, 2, 0); 

       View = objGrid; 


      } 
     } 
     public List<WrappedSelection<T>> WrappedItems = new List<WrappedSelection<T>>(); 
     public SelectMultipleBasePage(List<T> items) 
     { 
      WrappedItems = items.Select(item => new WrappedSelection<T>() { Item = item, IsSelected = false }).ToList(); 
      ListView mainList = new ListView() 
      { 
       ItemsSource = WrappedItems, 
       ItemTemplate = new DataTemplate(typeof(WrappedItemSelectionTemplate)), 
      }; 

      mainList.ItemSelected += (sender, e) => 
      { 
       if (e.SelectedItem == null) return; 
       var o = (WrappedSelection<T>)e.SelectedItem; 
       o.IsSelected = !o.IsSelected; 
       ((ListView)sender).SelectedItem = null; //de-select 
      }; 
      Content = mainList; 

      if (Device.OS == TargetPlatform.WinPhone) 
      { // fix issue where rows are badly sized (as tall as the screen) on WinPhone8.1 
       mainList.RowHeight = 40; 
       // also need icons for Windows app bar (other platforms can just use text) 
       ToolbarItems.Add(new ToolbarItem("All", "check.png", SelectAll, ToolbarItemOrder.Primary)); 
       ToolbarItems.Add(new ToolbarItem("None", "cancel.png", SelectNone, ToolbarItemOrder.Primary)); 
      } 
      else 
      { 
       ToolbarItems.Add(new ToolbarItem("All", null, SelectAll, ToolbarItemOrder.Primary)); 
       ToolbarItems.Add(new ToolbarItem("None", null, SelectNone, ToolbarItemOrder.Primary)); 
      } 
     } 
     void SelectAll() 
     { 
      foreach (var wi in WrappedItems) 
      { 
       wi.IsSelected = true; 
      } 
     } 
     void SelectNone() 
     { 
      foreach (var wi in WrappedItems) 
      { 
       wi.IsSelected = false; 
      } 
     } 
     public List<T> GetSelection() 
     { 
      return WrappedItems.Where(item => item.IsSelected).Select(wrappedItem => wrappedItem.Item).ToList(); 
     } 
    } 
} 

Listpage.cs：

using System; 
using System.Collections.Generic; 
using System.IO; 
using System.Linq; 
//using System.Reflection.Emit; 
using System.Text; 
using System.Xml.Serialization; 
using Xamarin.Forms; 

namespace ______ 
{ 
    public class ListPage : ContentPage 
    { 
     SelectMultipleBasePage<CheckItem> multiPage= null; 
     public ListPage() 
     { 
      loadlist(); 
     } 

     async void loadlist() 
     { 
      var items = new List<CheckItem>(); 
      items.Add(new CheckItem { Name = "Xamarin.com", Date = "01/01/2015", Image = "img.png" }); 
      items.Add(new CheckItem { Name = "Twitter", Date = "01/01/2015", Image = "img.png" }); 
      items.Add(new CheckItem { Name = "Facebook", Date = "01/01/2015", Image = "img.png" }); 

      if (multiPage == null) 
       multiPage = new SelectMultipleBasePage<CheckItem>(items) { Title = "Check all that apply" }; 

      await Navigation.PushAsync(multiPage); 
     } 
    } 
} 

App.cs：

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 

using Xamarin.Forms; 

namespace ____ 
{ 
    public class App : Application 
    { 
     public App() 
     { 
      MainPage = new NavigationPage(new ListPage()); 
     } 

     protected override void OnStart() 
     { 
      // Handle when your app starts 
     } 

     protected override void OnSleep() 
     { 
      // Handle when your app sleeps 
     } 

     protected override void OnResume() 
     { 
      // Handle when your app resumes 
     } 
    } 
} 

Answer 1

而不是做await Navigation.PushAsync(multiPage);更改爲：

Content = multiPage; 

這應該將您傳遞給NavigationPage的ListPage的頁面內容設置爲您在代碼中設置的SelectMultipleBasePage<T>。這應該是導航的第一頁，不應該有後退按鈕。

編輯： 對不起嘗試將其更改爲：Content = multiPage.Content;