C# 为什么绑定不足以刷新WP7（MVVM）中的UI

我正在尝试基于MVVM模式创建WP7应用程序，但在刷新TextBlock的绑定内容时遇到问题在当前状态下，我需要重新打开页面以刷新内容。我认为这与设置数据上下文有关，但我无法修复它

ViewModel.cs中的PropertyChangedEventHandler

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    private string _txtStatus = "";
    public string TxtStatus
    {
        get { return _txtStatus; }
        set
        {
            _txtStatus = value;
            NotifyPropertyChanged("TxtStatus");
        }
    }

public partial class App : Application
{
    private static ViewModel _viewModel { get; set; }
    public static ViewModel ViewModel
    {
        get { return _viewModel ?? (_viewModel = new ViewModel()); }
    }

public partial class Status : PhoneApplicationPage
{
    public Status()
    {
        InitializeComponent();
        DataContext = App.ViewModel;
    }

public class MqttService
{
    private readonly ViewModel _viewModel;

    public MqttService(ViewModel viewModel)
    {
        _viewModel = viewModel;
    }

    private void Log(string log)
    {
        _viewModel.TxtStatus = _viewModel.TxtStatus + log;
    }

    private void Connect()
    {
        _client.Connect(true);
        Log(MsgConnected + _viewModel.TxtBrokerUrl + ", " + _viewModel.TxtClientId + "\n");
        _viewModel.IsConnected = true;
    }

    private MqttService _mqttService;
    public MqttService MqttService
    {
        get { return _mqttService ?? (_mqttService = new MqttService(this)); }
    }

private void Log(string log)
{
    _viewModel.TxtStatus = _viewModel.TxtStatus + log;
}

private void Log(string log)
{
    Deployment.Current.Dispatcher.BeginInvoke(() =>
    {
        App.ViewModel.TxtStatus = log + App.ViewModel.TxtStatus;
    });
}

App.xaml.cs中的ViewModel属性

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    private string _txtStatus = "";
    public string TxtStatus
    {
        get { return _txtStatus; }
        set
        {
            _txtStatus = value;
            NotifyPropertyChanged("TxtStatus");
        }
    }

public partial class App : Application
{
    private static ViewModel _viewModel { get; set; }
    public static ViewModel ViewModel
    {
        get { return _viewModel ?? (_viewModel = new ViewModel()); }
    }

public partial class Status : PhoneApplicationPage
{
    public Status()
    {
        InitializeComponent();
        DataContext = App.ViewModel;
    }

public class MqttService
{
    private readonly ViewModel _viewModel;

    public MqttService(ViewModel viewModel)
    {
        _viewModel = viewModel;
    }

    private void Log(string log)
    {
        _viewModel.TxtStatus = _viewModel.TxtStatus + log;
    }

    private void Connect()
    {
        _client.Connect(true);
        Log(MsgConnected + _viewModel.TxtBrokerUrl + ", " + _viewModel.TxtClientId + "\n");
        _viewModel.IsConnected = true;
    }

    private MqttService _mqttService;
    public MqttService MqttService
    {
        get { return _mqttService ?? (_mqttService = new MqttService(this)); }
    }

private void Log(string log)
{
    _viewModel.TxtStatus = _viewModel.TxtStatus + log;
}

private void Log(string log)
{
    Deployment.Current.Dispatcher.BeginInvoke(() =>
    {
        App.ViewModel.TxtStatus = log + App.ViewModel.TxtStatus;
    });
}

在StatusPage.xaml.cs中设置DataContext

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    private string _txtStatus = "";
    public string TxtStatus
    {
        get { return _txtStatus; }
        set
        {
            _txtStatus = value;
            NotifyPropertyChanged("TxtStatus");
        }
    }

public partial class App : Application
{
    private static ViewModel _viewModel { get; set; }
    public static ViewModel ViewModel
    {
        get { return _viewModel ?? (_viewModel = new ViewModel()); }
    }

public partial class Status : PhoneApplicationPage
{
    public Status()
    {
        InitializeComponent();
        DataContext = App.ViewModel;
    }

public class MqttService
{
    private readonly ViewModel _viewModel;

    public MqttService(ViewModel viewModel)
    {
        _viewModel = viewModel;
    }

    private void Log(string log)
    {
        _viewModel.TxtStatus = _viewModel.TxtStatus + log;
    }

    private void Connect()
    {
        _client.Connect(true);
        Log(MsgConnected + _viewModel.TxtBrokerUrl + ", " + _viewModel.TxtClientId + "\n");
        _viewModel.IsConnected = true;
    }

    private MqttService _mqttService;
    public MqttService MqttService
    {
        get { return _mqttService ?? (_mqttService = new MqttService(this)); }
    }

private void Log(string log)
{
    _viewModel.TxtStatus = _viewModel.TxtStatus + log;
}

private void Log(string log)
{
    Deployment.Current.Dispatcher.BeginInvoke(() =>
    {
        App.ViewModel.TxtStatus = log + App.ViewModel.TxtStatus;
    });
}

在StatusPage.xaml中绑定

<TextBlock x:Name="TxtStatus" Text="{Binding Path=TxtStatus, Mode=OneWay}" Width="450" TextWrapping="Wrap" HorizontalAlignment="Left" VerticalAlignment="Top" />

ViewModel.cs中的MqttService属性

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    private string _txtStatus = "";
    public string TxtStatus
    {
        get { return _txtStatus; }
        set
        {
            _txtStatus = value;
            NotifyPropertyChanged("TxtStatus");
        }
    }

public partial class App : Application
{
    private static ViewModel _viewModel { get; set; }
    public static ViewModel ViewModel
    {
        get { return _viewModel ?? (_viewModel = new ViewModel()); }
    }

public partial class Status : PhoneApplicationPage
{
    public Status()
    {
        InitializeComponent();
        DataContext = App.ViewModel;
    }

public class MqttService
{
    private readonly ViewModel _viewModel;

    public MqttService(ViewModel viewModel)
    {
        _viewModel = viewModel;
    }

    private void Log(string log)
    {
        _viewModel.TxtStatus = _viewModel.TxtStatus + log;
    }

    private void Connect()
    {
        _client.Connect(true);
        Log(MsgConnected + _viewModel.TxtBrokerUrl + ", " + _viewModel.TxtClientId + "\n");
        _viewModel.IsConnected = true;
    }

    private MqttService _mqttService;
    public MqttService MqttService
    {
        get { return _mqttService ?? (_mqttService = new MqttService(this)); }
    }

private void Log(string log)
{
    _viewModel.TxtStatus = _viewModel.TxtStatus + log;
}

private void Log(string log)
{
    Deployment.Current.Dispatcher.BeginInvoke(() =>
    {
        App.ViewModel.TxtStatus = log + App.ViewModel.TxtStatus;
    });
}

---

现在我想知道是否有某种循环引用问题（MqttService ViewModel）。我不确定，我觉得不错。

您的代码在

WPF

.NET4.0

因此，您的属性

TxtStatus

可能永远不会得到字符串

_txtStatus ="new status"; // wrong
TxtStatus = "new status"; // right

或者您的

x:Name=“TxtStatus”

会受到一些干扰，但这将是一个基于Windows-Phone-7的问题，谢谢大家。在写了关于线程的评论之后，我做了一些研究，发现了以下内容：。我改变了TxtStatus的设置方式，现在它工作得很好。：）

（错误）MqttService.cs中TxtStatus的设置值

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    private string _txtStatus = "";
    public string TxtStatus
    {
        get { return _txtStatus; }
        set
        {
            _txtStatus = value;
            NotifyPropertyChanged("TxtStatus");
        }
    }

public partial class App : Application
{
    private static ViewModel _viewModel { get; set; }
    public static ViewModel ViewModel
    {
        get { return _viewModel ?? (_viewModel = new ViewModel()); }
    }

public partial class Status : PhoneApplicationPage
{
    public Status()
    {
        InitializeComponent();
        DataContext = App.ViewModel;
    }

public class MqttService
{
    private readonly ViewModel _viewModel;

    public MqttService(ViewModel viewModel)
    {
        _viewModel = viewModel;
    }

    private void Log(string log)
    {
        _viewModel.TxtStatus = _viewModel.TxtStatus + log;
    }

    private void Connect()
    {
        _client.Connect(true);
        Log(MsgConnected + _viewModel.TxtBrokerUrl + ", " + _viewModel.TxtClientId + "\n");
        _viewModel.IsConnected = true;
    }

    private MqttService _mqttService;
    public MqttService MqttService
    {
        get { return _mqttService ?? (_mqttService = new MqttService(this)); }
    }

private void Log(string log)
{
    _viewModel.TxtStatus = _viewModel.TxtStatus + log;
}

private void Log(string log)
{
    Deployment.Current.Dispatcher.BeginInvoke(() =>
    {
        App.ViewModel.TxtStatus = log + App.ViewModel.TxtStatus;
    });
}

（良好）MqttService.cs中TxtStatus的设置值

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    private string _txtStatus = "";
    public string TxtStatus
    {
        get { return _txtStatus; }
        set
        {
            _txtStatus = value;
            NotifyPropertyChanged("TxtStatus");
        }
    }

public partial class App : Application
{
    private static ViewModel _viewModel { get; set; }
    public static ViewModel ViewModel
    {
        get { return _viewModel ?? (_viewModel = new ViewModel()); }
    }

public partial class Status : PhoneApplicationPage
{
    public Status()
    {
        InitializeComponent();
        DataContext = App.ViewModel;
    }

public class MqttService
{
    private readonly ViewModel _viewModel;

    public MqttService(ViewModel viewModel)
    {
        _viewModel = viewModel;
    }

    private void Log(string log)
    {
        _viewModel.TxtStatus = _viewModel.TxtStatus + log;
    }

    private void Connect()
    {
        _client.Connect(true);
        Log(MsgConnected + _viewModel.TxtBrokerUrl + ", " + _viewModel.TxtClientId + "\n");
        _viewModel.IsConnected = true;
    }

    private MqttService _mqttService;
    public MqttService MqttService
    {
        get { return _mqttService ?? (_mqttService = new MqttService(this)); }
    }

private void Log(string log)
{
    _viewModel.TxtStatus = _viewModel.TxtStatus + log;
}

private void Log(string log)
{
    Deployment.Current.Dispatcher.BeginInvoke(() =>
    {
        App.ViewModel.TxtStatus = log + App.ViewModel.TxtStatus;
    });
}

---

输出视图中有任何绑定错误吗？我看不出您的代码有任何错误。您如何更新要在文本块中显示的值？也许您可以添加一个

，UpdateSourceTrigger=PropertyChanged

应用程序中是否存在多线程？更具体地说，

TxtStatus

是否在UI线程中更新？您可以在ViewModel上TxtStatus的setter中设置断点，并查看更新属性时是否命中它。如果它被击中，你可能有2个并发视图模型；一个连接到视图，另一个连接到服务。