Mvvm奇怪的使者行为 [英] Mvvm strange messenger behaviour

问题描述

我正在尝试在两个ViewModel之间传递用户。为此，我使用的是MVVM light Messenger框架。即使遇到断点，我尝试操作传递给第二个ViewModel的模型，但是一些绑定到属性的TextBlocks也不会更新。



我尝试过：



以下是当有人点击登录按钮时我通过用户的方式：

I am trying to pass a User between two ViewModels. To do this I am using the MVVM light Messenger framework. Even though a breakpoint is hit where I try to action the model that is passed to the second ViewModel, some TextBlocks that are bound to properties are not updated.

What I have tried:

Here is how I pass the 'User' when someone clicks a login button:

#region Login
private DelegateCommand _loginCommand;
public ICommand LoginCommand
{
    get
    {
        _loginCommand = new DelegateCommand(param => Login());
        return _loginCommand;
    }
}

private async void Login()
{
    var waitWindow = new PleaseWaitWindow();
    waitWindow.Show();

    if (await LoginCheck())
    {
        // TODO: Navigate to the DashboardView
        Messenger.Default.Send(new ChangePage(typeof(DashboardViewModel)));
        Messenger.Default.Send(_chosenUser);
    }

    waitWindow.Close();
}
#endregion

以下是我订阅该邮件并使用其内容的方式：

Here is how I subscribe to that message and use its contents:

public DashboardViewModel()
{
    Messenger.Default.Register<User>(this, OnUserReceived);
    Messenger.Default.Register<ChangePage>(this, ChangePage); // Register to Messenger to change Views hosted in ContentControl
}

private void OnUserReceived(User user)
{
    FirstName = user.FirstName; // Breakpoint is hit here with correct value
    LastName = user.LastName;
}

和绑定到FirstName和LastName属性的两个TextBlock ..：

And the two TextBlocks that are bound to the FirstName and LastName properties..:

<StackPanel VerticalAlignment="Center" Margin="5">
    <TextBlock Text="{Binding FirstName}" Foreground="White" Margin="5" FontSize="18"/>
    <TextBlock Text="{Binding LastName}" Foreground="White" FontWeight="Bold" Margin="5" FontSize="20"/>
</StackPanel>

如果我设置一个断点来操作Messenger，那么FirstName和LastName设置为正确的价值观但是，TextBlocks没有更新，它们的文本仍然是空的。



我在DashboardView上实现了一个测试按钮，只需设置FirstName =Test;这确实更新TextBlock说文本所以我很困惑为什么传入一种类型的用户并使用其FirstName和LastName不起作用。



编辑：

If I set a breakpoint where I action the Messenger then FirstName and LastName are set to the correct values. However, the TextBlocks are not updated and their text remains null.

I have implemented a test button on the DashboardView that simply sets FirstName ="Test"; and this does update the TextBlock to say Text so I am confused as to why passing in a type of User and using its FirstName and LastName doesn't work.

private void OnUserReceived(User user)
{
    Application.Current.Dispatcher.Invoke(() =>
    {
        FirstName = user.FirstName;
        LastName = user.LastName;
    });
}

推荐答案

这种行为很正常，

因为信使不同线程。



我也有过这种现象。



您应该使用调度员：

This behaviour is quite normal,
as the messenger is on a different thread.

I also had this phenomenon once.

You should use a dispatcher:

Application.Current.Dispatcher.Invoke(() =>
{
    FirstName = user.FirstName; // Breakpoint is hit here with correct value
    LastName = user.LastName;
});

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