UWP 加载指示器未出现

Question

我有一个 UWP 应用程序，我想在加载数据时显示一个内容对话框。

这是我的加载对话框，通过 LoadedCommand 调用。

    private async Task LoadDataAsync()
    {
            await dialogService.ShowLoadingDialogAsync();

            await LoadPaymentsAsync(new PaymentListFilterChangedMessage { TimeRangeStart = DateTime.Now.AddYears(DEFAULT_MONTH_BACK) });
            //Refresh balance control with the current account
            await BalanceViewModel.UpdateBalanceCommand.ExecuteAsync();

            await dialogService.HideLoadingDialogAsync();
    }

我还尝试通过 DispatcherHelper 调用它：

    private async Task LoadDataAsync()
    {
        await DispatcherHelper.ExecuteOnUIThreadAsync(async () =>
        {
            await dialogService.ShowLoadingDialogAsync();

            await LoadPaymentsAsync(new PaymentListFilterChangedMessage { TimeRangeStart = DateTime.Now.AddYears(DEFAULT_MONTH_BACK) });
            //Refresh balance control with the current account
            await BalanceViewModel.UpdateBalanceCommand.ExecuteAsync();

            await dialogService.HideLoadingDialogAsync();
        });
    }

但这并没有改变任何事情。 DialogService 中的方法如下所示：

    /// <summary>
    /// Shows a loading Dialog.
    /// </summary>
    public async Task ShowLoadingDialogAsync(string? message = null)
    {
        // Be sure no other dialog is open.
        await HideLoadingDialogAsync();

        loadingDialog = new LoadingDialog { Text = message ?? Strings.LoadingLabel };

        CoreApplicationView coreWindow = CoreApplication.MainView;

        // Dispatcher needed to run on UI Thread
        CoreDispatcher dispatcher = coreWindow.CoreWindow.Dispatcher;

        // RunAsync all of the UI info.
        await dispatcher.RunAsync(CoreDispatcherPriority.High,
            async () =>
            {
                await loadingDialog.ShowAsync();
            });
    }

    /// <summary>
    /// Hides the previously opened Loading Dialog.
    /// </summary>
    public Task HideLoadingDialogAsync()
    {
        loadingDialog?.Hide();
        return Task.CompletedTask;
    }

在其他情况下很有趣，例如，当我从网络服务而不是数据库加载数据时，这确实没有任何问题。

Answer 1

UWP Loading indicator does not appear

在测试过程中，LoadingDialog Text 属性导致了问题，如果你想让 Text 属性可以影响 xaml 内容，请将其作为依赖属性喜欢下面的内容。

Xaml

<Grid>
    <TextBlock
        x:Name="main_content"
        VerticalAlignment="Center"
        Text="{x:Bind Text, Mode=OneWay}" />
</Grid>

代码隐藏

public sealed partial class LoadingDialog : ContentDialog
{
    public LoadingDialog()
    {
        this.InitializeComponent();
    }

    public string Text
    {
        get { return (string)GetValue(TextProperty); }
        set { SetValue(TextProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Text.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty TextProperty =
        DependencyProperty.Register("Text", typeof(string), typeof(LoadingDialog), new PropertyMetadata(0));




    private void ContentDialog_PrimaryButtonClick(ContentDialog sender, ContentDialogButtonClickEventArgs args)
    {
    }

    private void ContentDialog_SecondaryButtonClick(ContentDialog sender, ContentDialogButtonClickEventArgs args)
    {
    }
}

现在您可以使用 DialogService 正确显示对话框。

private async void MainPage_Loaded(object sender, RoutedEventArgs e)
{
    await dialogService.ShowLoadingDialogAsync();
    await Task.Delay(3000);
    await dialogService.HideLoadingDialogAsync();
}

更新

另一种猜测是加载过程非常快，导致对话框在显示之前就消失了。所以你尝试在之后手动添加任务延迟 await BalanceViewModel.UpdateBalanceCommand.ExecuteAsync();行

UWP 加载指示器未出现

UWP Loading indicator does not appear

uwp

uwp-xaml