.netMaui系結值多個級別深

如何將系結從 a 傳遞Page到 a View？

我有這個頁面（Xaml）

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:views="clr-namespace:DataBindingTests.Views"
             xmlns:model="clr-namespace:DataBindingTests.ViewModels"
             x:Class="DataBindingTests.Pages.CoolePage"
             Title="CoolePage"
             x:DataType="model:CoolesModel">
    <VerticalStackLayout>
        <Label Text="{Binding YourName}"></Label>
        <views:MainView YourName="{Binding YourName}"></views:MainView>
        <Button Command="{Binding ChangeNameCommand}"></Button>
    </VerticalStackLayout>
</ContentPage>

及其背后的代碼：

using DataBindingTests.ViewModels;

namespace DataBindingTests.Pages;

public partial class CoolePage : ContentPage
{
    public CoolePage()
    {
        this.BindingContext = new CoolesModel();
        InitializeComponent();
    }
}

如果我將一個字串傳遞到我的 MainView 中，它會起作用并且所有事件都會被觸發。當我使用系結時，它不會。在這個簡單的測驗中，應用程式應該顯示兩次相同的名稱，但只有 ContentPage 的 Label 具有YourName列印的屬性

<views:MainView YourName="Lars"></views:MainView> <-- 有效

<views:MainView YourName="{Binding YourName}"></views:MainView> <-- 不起作用

這是 MainView 的 Xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentView xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:views="clr-namespace:DataBindingTests.Views"
             x:Class="DataBindingTests.Views.MainView">
    <VerticalStackLayout>
        <Label Text="{Binding YourName}"
            VerticalOptions="Center" 
            HorizontalOptions="Center" />
    </VerticalStackLayout>
</ContentView>

這是 MainView 的 CodeBehind

namespace DataBindingTests.Views;

public partial class MainView : ContentView
{
    public String YourName
    {
        get
        {
            String value = (String)GetValue(MainView.YourNameProperty);
            return value;
        }
        set
        {
            SetValue(MainView.YourNameProperty, value);
        }
    }

    public static readonly BindableProperty YourNameProperty = BindableProperty.Create(nameof(YourName)
    , typeof(String)
    , typeof(MainView), defaultBindingMode:BindingMode.TwoWay, propertyChanged: OnYourNameChanged);

    static void OnYourNameChanged(BindableObject bindable, object oldValue, object newValue)
    {
        Console.WriteLine(newValue);
    }

    public MainView()
    {
        this.BindingContext = this; // Ignore ParentContext
        InitializeComponent();
    }
}

uj5u.com熱心網友回復：

您可以this.BindingContext = this;從以下建構式中洗掉代碼MainView.xaml.cs：

 public MainView()
    {
        //this.BindingContext = this;
        InitializeComponent();
    }

更新：

上面的代碼只能作業，因為視圖中的屬性和頁面具有相同的名稱。

在這種情況下，您可以修改MainView.xaml如下代碼：

 <?xml version="1.0" encoding="utf-8" ?> 
<ContentView xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MauiApp929.MainView"
             x:Name="TestControlView"
             >
    <VerticalStackLayout>
        <Label   Text="{Binding Source={x:Reference TestControlView}, Path=YourName}"
            VerticalOptions="Center" 
            HorizontalOptions="Center" />
    </VerticalStackLayout>
</ContentView>

MainView.xaml.cs

public partial class MainView : ContentView 
{

    public String YourName
    {
        get
        {
            String value = (String)GetValue(YourNameProperty);
            return value;
        }
        set
        {
            SetValue(YourNameProperty, value);
        }
    }

    public static readonly BindableProperty YourNameProperty = BindableProperty.Create(nameof(YourName)
    , typeof(String)
    , typeof(MainView), defaultBindingMode: BindingMode.TwoWay, propertyChanged: OnYourNameChanged);

    static void OnYourNameChanged(BindableObject bindable, object oldValue, object newValue)
    {
        Console.WriteLine("-----------------> " newValue);
    }
    public MainView()
??????{
????????????InitializeComponent();

       // this.BindingContext = this;
    }
}

CoolesModel.cs

public class CoolesModel 
{
    //  public string YourName { get; set; }
    public string Name { get; set; }

    public string TestName { get; set; }

    public ICommand ChangeNameCommand => new Command(changeMethod);

    private void changeMethod()
    {

    }

    public CoolesModel() {
        //YourName = "abc";
        Name = "abc";

        TestName = "test123...";
    }
}

MainPage.xaml.cs

<?xml version="1.0" encoding="utf-8" ?> 
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:mauiapp929="clr-namespace:MauiApp929"
             x:Class="MauiApp929.MainPage">
  
    <ScrollView>
        <VerticalStackLayout>
            <Label Text="{Binding Name}"></Label>
            <mauiapp929:MainView YourName="{Binding TestName}"></mauiapp929:MainView>
            <Button Command="{Binding ChangeNameCommand}"></Button>
        </VerticalStackLayout>
    </ScrollView>

</ContentPage>

uj5u.com熱心網友回復：

In this simple test, the app should display two times the same name, but only the Label of the ContentPage has the YourName property printed

You're overwriting your binding context half way through for some reason, and the context your page binding resolves (the normal way of using it, the parent context) is different than what you actually see on the screen (which is your this.BindingContext = this). And you never set your second context's property.

標籤：C＃xml毛伊岛

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