绑定文本需要在Xamarin中重新加载页面

问题描述

我正在研究Xamarin.Forms应用程序。我在viewmodel页面中设置了一个条件，然后通过绑定更改了标签文本和图像按钮的可见性。

但是问题是，当我打开页面时，屏幕为空，但是当我刷新页面时，它会显示文本。

下面是xml和.cs页面的代码。

Indexviewmodel.cs

    public override async Task InitializeAsync(object navigationData)
    {
        var firstname = await SecureStorage.GetAsync("firstname");

        if (firstname == null)
        {
            var RegisteredUserID = await SecureStorage.GetAsync("RegisteredUserID");

            _indexText = "Waiting for Identity to be Issued";
            IsQRScannerVisible = false;
        }
        else
        {
            _indexText = "Your App is Ready";
            IsQRScannerVisible = true;
        }

        await base.InitializeAsync(navigationData);
    }

可绑定属性

    private string _indexText;
    public string IndexText
    {
        get => _indexText;
        set => this.RaiseAndSetIfChanged(ref _indexText,value);
    }

    public bool IsQRScannerVisible { get; private set; }

IndexPage.xml

<Label
    FontSize="14"
    HorizontalOptions="Center"
    Text="{Binding IndexText}"
    TextColor="White"
    Margin="0,-26,150">
</Label>

<ImageButton 
    Source="drawable/qrcode_icon.png"
    HorizontalOptions="Center"
    VerticalOptions="CenterandExpand"
    WidthRequest = "70"
    HeightRequest = "70"
    MinimumHeightRequest = "70"
    MinimumWidthRequest = "70"
    BackgroundColor="#004B86"
    IsVisible="{Binding IsQRScannerVisible}"
    Command="{Binding ScanVerificationCommand}"/>

解决方法

您正在设置内部字段

_indexText = "Waiting for Identity to be Issued";

这样做会绕过PropertyChanged事件。而是使用公共财产

IndexTest = "Waiting for Identity to be Issued";