尽管没有错误，页面根本不会显示

Posted 2023-02-16

【中文标题】尽管没有错误，页面根本不会显示

【英文标题】：Page will not display at all despite no errors

【发布时间】：2020-03-22 20:25:27

【问题描述】：

过去一个小时我一直在反复阅读我的代码，似乎无法理解为什么我现在添加的更改不允许我的页面显示（未显示的页面是 NameEntryPage）。该应用程序从具有两个按钮的 StartPage 开始，允许用户选择 One Player Game 或 Two Player Game。如果用户选择两个玩家游戏，那么它导航到 NameEntryPage，用户可以在其中输入两个玩家的名称。 NameEntryPage 有一个按钮，单击该按钮会传递输入的名称并导航到 TwoPlayerPage。我已经检查了 StartPage、OnePlayerPage 和 TwoPlayerPage，它们仍然有效。但是，NameEntryPage 不会加载任何内容（并且 StartPage 上的带您到那里的按钮也不起作用。要检查其他页面，我必须更改 App() 中的代码才能从这些页面开始）

App() 代码

 public App()
     
         InitializeComponent();
         MainPage = new NavigationPage(new Views.NameEntryPage());
     

NameEntryPage.xaml 代码

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:d="http://xamarin.com/schemas/2014/forms/design"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         mc:Ignorable="d"
         x:Class="SampleApp.Views.NameEntryPage">
<ContentPage.Content>
    <StackLayout Margin="20">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="*" />
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>
        </Grid>
        <Entry
               x:Name="EntryNameP1"
               Placeholder="Enter a name for Player 1"
               Text="Binding NameP1"
               Grid.Row="0" Grid.Column="0"/>

        <Entry x:Name="EntryNameP2"
               Placeholder="Enter a name for Player 2"
               Text="Binding NameP2"
               Grid.Row="1" Grid.Column="0"/>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>
            <Button Grid.Column="0" 
                Text="Start"/>
        </Grid>
    </StackLayout>
</ContentPage.Content>

后面的代码

namespace SampleApp.Views

    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class NameEntryPage : ContentPage
    
        public NameEntryPage()
        
            NavigationPage.SetHasNavigationBar(this, false);
            InitializeComponent();
            BindingContext = new NameEntryPageViewModel(Navigation, EntryNameP1.Text, EntryNameP2.Text);
        
    

虚拟机代码

public class NameEntryPageViewModel : INotifyPropertyChanged



    public INavigation Navigation  get; set; 

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
    
        var changed = PropertyChanged;
        if (changed == null)
            return;

        changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
    

    private string nameP1;

    public string NameP1
    
        get
        
            return NameP1;
        
        set
        
            if (NameP1 != value)
            
                nameP1 = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("NameP1"));
            
        
    

    private string nameP2;

    public string NameP2
    
        get
        
            return NameP2;
        
        set
        
            if (NameP2 != value)
            
                nameP2 = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("NameP1"));
            
        
    


    public Command StartGameCommand  get; set; 


    public NameEntryPageViewModel(INavigation navigation, string name1, string name2)
    

        nameP1 = name1;
        nameP2 = name2;
        this.Navigation = navigation;
        StartGameCommand = new Command(() => StartGame(nameP1, nameP2));

    

    public NameEntryPageViewModel(INavigation navigation)
    
        nameP1 = "Player 1";
        nameP2 = "Player 2";
        this.Navigation = navigation;
        StartGameCommand = new Command(() => StartGame(nameP1, nameP2));

    

    private void StartGame(string name1, string name2)
    

        this.Navigation.PushAsync(new Views.TwoPlayerPage(name1, name2));
    

【参考方案1】：

这将创建一个无限循环

public string NameP1

    get
    
        return NameP1;
    

NameP1 会调用NameP1 的getter，它会递归调用NameP1 的getter，直到你崩溃

您的 getter 应该返回 private nameP1 变量

public string NameP1

    get
    
        return namep1;