Question

我目前使用mvvm light框架开发了一个metro风格的应用程序。

我有一些命令，例如DeleteSelectedAppUserCommand。用户必须确认他确实要删除该用户。所以我在静态类“DialogService”中编写了一个静态方法“ShowMessageBoxYesNo”。

public static async Task<bool> ShowMessageBoxYesNo(string message, string title)
{
    MessageDialog dlg = new MessageDialog(message, title);

    // Add commands and set their command ids
    dlg.Commands.Add(new UICommand("Yes", null, 0));
    dlg.Commands.Add(new UICommand("No", null, 1));

    // Set the command that will be invoked by default
    dlg.DefaultCommandIndex = 1;

    // Show the message dialog and get the event that was invoked via the async operator
    IUICommand result = await dlg.ShowAsync();

    return (int)result.Id == 0;
}

在我要调用此方法的命令中，但我不知道如何... 这不可能吗？以下代码不起作用！

#region DeleteSelectedAppUserCommand

/// <summary>
/// The <see cref="DeleteSelectedAppUserCommand" /> RelayCommand's name.
/// </summary>
private RelayCommand _deleteSelectedAppUserCommand;

/// <summary>
/// Gets the DeleteSelectedAppUserCommand RelayCommand.
/// </summary>
public RelayCommand DeleteSelectedAppUserCommand
{
    get
    {
        return _deleteSelectedAppUserCommand
            ?? (_deleteSelectedAppUserCommand = new RelayCommand(
            () =>
            {
                if (await DialogService.ShowMessageBoxYesNo("Do you really want delete the user?","Confirm delete")
                {
                    AppUsers.Remove(SelectedEditAppUser);
                }
            },
            () =>
                this.SelectedEditAppUser != null
            ));
    }
}
#endregion

感谢您的帮助！迈克尔

Answer 1

如果要在lambda中使用await，则必须将该lambda标记为async：

new RelayCommand(
    async () =>
    {
        if (await DialogService.ShowMessageBoxYesNo("Do you really want delete the user?", "Confirm delete")
        {
            AppUsers.Remove(SelectedEditAppUser);
        }
    },
    () =>
        this.SelectedEditAppUser != null
    )

这会创建一个void - 返回async方法，通常应该避免这种方法。但我觉得这里有意义，因为你基本上是在实现一个事件处理程序。事件处理程序是唯一通常使用void - 返回async方法的地方。

如何使用MVVM Light从MessageDialog获取返回值？

1 个答案: