---
lang: ja-jp
breaks: true
---
# WinUI 3 ContentDialog から ContentDialog を開くことは出来ない 2022-11-24

> AppWindow 内または XAML Islands 内の ContentDialog
> https://learn.microsoft.com/ja-jp/windows/apps/design/controls/dialogs-and-flyouts/dialogs#contentdialog-in-appwindow-or-xaml-islands

:::warning
1 つのスレッドで一度に開くことのできる ContentDialog は 1 つだけです。 2 つの ContentDialog を開こうとすると、個別の AppWindow で開く場合でも、例外がスローされます。

以下の例外が発生する。

System.Runtime.InteropServices.COMException: 'An async operation was not properly started. (0x80000019)'

:::

:::info
この仕様は、UWPも同じ。
:::

## DialogPage.xaml

<Page
    x:Class="App4_DisplayingDialogsFromDialog.DialogPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App4_DisplayingDialogsFromDialog"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <Grid>
        <StackPanel VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
            <!-- Content body -->
            <TextBlock Text="Lorem ipsum dolor sit amet, adipisicing elit." TextWrapping="Wrap" />
            <CheckBox Content="Upload your content to the cloud."/>
        </StackPanel>

    </Grid>
</Page>

## MainWindow.xaml.cs

public sealed partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();
    }

    private async Task ShowContentDialog()
    {
        ContentDialog dialog = new ContentDialog();
        dialog.Title = "Save your work?";
        dialog.PrimaryButtonText = "Save";
        dialog.SecondaryButtonText = "Don't Save";
        dialog.CloseButtonText = "Cancel";
        dialog.DefaultButton = ContentDialogButton.Primary;
        dialog.Content = new DialogPage();

        dialog.XamlRoot = this.Content.XamlRoot;

        dialog.PrimaryButtonClick += Dialog_PrimaryButtonClick;

        var result = await dialog.ShowAsync();
    }

    private async void myButton_Click(object sender, RoutedEventArgs e)
    {
        myButton.Content = "Clicked";

        await ShowContentDialog();
    }

    private async void Dialog_PrimaryButtonClick(
        ContentDialog sender,
        ContentDialogButtonClickEventArgs args
        )
    {
        ContentDialog contentDialog = new ContentDialog
        {
            Title = "ダイアログタイトル",
            Content = "コンテンツ（メッセージ内容）",
            CloseButtonText = "ボタンに表示するテキスト"
        };

        contentDialog.XamlRoot = this.Content.XamlRoot;

        ContentDialogResult result = await contentDialog.ShowAsync();
    }
}

###### tags: `WinUI 3` `ContentDialog`