WPF双向绑定无法正常工作

Question

我有一个数据上下文(UserPreferences)分配给我的主窗口,以及一个文本框,它双向绑定到上下文中的一个数据上下文属性(CollectionDevice)中的属性.

加载窗口时,文本框不会绑定到模型中的属性.我在调试器中验证数据上下文是否设置为模型对象,并且模型的属性已正确分配.然而,我得到的是一系列带有0的文本框.

当我将数据输入文本框时,数据将在模型中更新.当我加载数据并将其应用于数据上下文时,问题才会发生,文本框不会更新.

当我将模型保存到数据库时,将从文本框中保存正确的数据.当我从数据库恢复模型时,将应用正确的数据.当模型应用于构造函数中的数据上下文时,文本框的datacontext包含正确的数据,并且它的属性按原样分配.问题是UI没有反映这一点.

XAML

<Window.DataContext>
    <models:UserPreferences />
</Window.DataContext>

        <!-- Wrap pannel used to store the manual settings for a collection device. -->
        <StackPanel Name="OtherCollectionDevicePanel">
            <StackPanel Orientation="Horizontal">
                <TextBlock VerticalAlignment="Center" Margin="10, 10, 0, 0" Text="Baud Rate" />
                <TextBox Name="BaudRateTextBox" Text="{Binding Path=SelectedCollectionDevice.BaudRate, Mode=TwoWay}" Margin="10, 10, 0, 0" MinWidth="80" ></TextBox>
            </StackPanel>
            <WrapPanel>
                <TextBlock VerticalAlignment="Center" Margin="10, 10, 0, 0" Text="Com Port" />
                <TextBox Text="{Binding Path=SelectedCollectionDevice.ComPort, Mode=TwoWay}" Margin="10, 10, 0, 0" MinWidth="80" ></TextBox>
            </WrapPanel>
            <WrapPanel>
                <TextBlock VerticalAlignment="Center" Margin="10, 10, 0, 0" Text="Data Points" />
                <TextBox Text="{Binding Path=SelectedCollectionDevice.DataPoints, Mode=TwoWay}" Margin="10, 10, 0, 0" MinWidth="80" ></TextBox>
            </WrapPanel>
            <WrapPanel Orientation="Horizontal">
                <TextBlock VerticalAlignment="Center" Margin="10, 10, 0, 0" Text="WAAS" />
                <CheckBox IsChecked="{Binding Path=SelectedCollectionDevice.WAAS, Mode=TwoWay}" Content="Enabled" Margin="20, 0, 0, 0" VerticalAlignment="Bottom"></CheckBox>
            </WrapPanel>
        </StackPanel>

Model < - Datacontext.

/// <summary>
/// Provides a series of user preferences.
/// </summary>
[Serializable]
public class UserPreferences : INotifyPropertyChanged
{
    private CollectionDevice selectedCollectionDevice;

    public UserPreferences()
    {
        this.AvailableCollectionDevices = new List<CollectionDevice>();

        var yuma1 = new CollectionDevice
        {
            BaudRate = 4800,
            ComPort = 31,
            DataPoints = 1,
            Name = "Trimble Yuma 1",
            WAAS = true
        };

        var yuma2 = new CollectionDevice
        {
            BaudRate = 4800,
            ComPort = 3,
            DataPoints = 1,
            Name = "Trimble Yuma 2",
            WAAS = true
        };

        var toughbook = new CollectionDevice
        {
            BaudRate = 4800,
            ComPort = 3,
            DataPoints = 1,
            Name = "Panasonic Toughbook",
            WAAS = true
        };


        var other = new CollectionDevice
        {
            BaudRate = 0,
            ComPort = 0,
            DataPoints = 0,
            Name = "Other",
            WAAS = false
        };

        this.AvailableCollectionDevices.Add(yuma1);
        this.AvailableCollectionDevices.Add(yuma2);
        this.AvailableCollectionDevices.Add(toughbook);
        this.AvailableCollectionDevices.Add(other);

        this.SelectedCollectionDevice = this.AvailableCollectionDevices.First();
    }

    /// <summary>
    /// Gets or sets the GPS collection device.
    /// </summary>
    public CollectionDevice SelectedCollectionDevice
    {
        get
        {
            return selectedCollectionDevice;
        }
        set
        {
            selectedCollectionDevice = value;
            this.OnPropertyChanged("SelectedCollectionDevice");
        }
    }

    /// <summary>
    /// Gets or sets a collection of devices that can be used for collecting GPS data.
    /// </summary>
    [Ignore]
    [XmlIgnore]
    public List<CollectionDevice> AvailableCollectionDevices { get; set; }

    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Notifies objects registered to receive this event that a property value has changed.
    /// </summary>
    /// <param name="propertyName">The name of the property that was changed.</param>
    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

CollectionDevice < - 文本框绑定的位置.

/// <summary>
/// CollectionDevice model
/// </summary>
[Serializable]
public class CollectionDevice : INotifyPropertyChanged
{
    /// <summary>
    /// Gets or sets the COM port.
    /// </summary>
    private int comPort;

    /// <summary>
    /// Gets or sets a value indicating whether [waas].
    /// </summary>
    private bool waas;

    /// <summary>
    /// Gets or sets the data points.
    /// </summary>
    private int dataPoints;

    /// <summary>
    /// Gets or sets the baud rate.
    /// </summary>
    private int baudRate;

    /// <summary>
    /// Gets or sets the name.
    /// </summary>
    public string Name { get; set; }

    /// <summary>
    /// Gets or sets the COM port.
    /// </summary>
    public int ComPort
    {
        get
        {
            return this.comPort;
        }

        set
        {
            this.comPort= value;
            this.OnPropertyChanged("ComPort");
        }
    }

    /// <summary>
    /// Gets or sets the COM port.
    /// </summary>
    public bool WAAS
    {
        get
        {
            return this.waas;
        }

        set
        {
            this.waas = value;
            this.OnPropertyChanged("WAAS");
        }
    }

    /// <summary>
    /// Gets or sets the COM port.
    /// </summary>
    public int DataPoints
    {
        get
        {
            return this.dataPoints;
        }

        set
        {
            this.dataPoints = value;
            this.OnPropertyChanged("DataPoints");
        }
    }

    /// <summary>
    /// Gets or sets the COM port.
    /// </summary>
    public int BaudRate
    {
        get
        {
            return this.baudRate;
        }

        set
        {
            this.baudRate = value;
            this.OnPropertyChanged("BaudRate");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Notifies objects registered to receive this event that a property value has changed.
    /// </summary>
    /// <param name="propertyName">The name of the property that was changed.</param>
    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public override string ToString()
    {
        return this.Name;
    }
}

有人能指出我正确的方向吗？我认为这个问题是我在XAML中的约束力; 我找不到它.我需要它是双向绑定的,因为数据可以在模型中的应用程序生命周期内随时更改(数据库通过同步更新)并且UI需要反映这些更改,但用户可以通过以下方式将更改应用于模型用户界面.

更新1

我试图强制更新文本框数据绑定,但这不起作用.

BindingExpression be = this.BaudRateTextBox.GetBindingExpression(TextBox.TextProperty);
be.UpdateSource();

我也尝试设置UpdateSourceTrigger到PropertyChanged和似乎没有要么解决问题.

<TextBox Name="BaudRateTextBox" Text="{Binding Path=SelectedCollectionDevice.BaudRate, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Margin="10, 10, 0, 0" MinWidth="80" ></TextBox>

更新2

我试图跟随微软的一些文档,它似乎没有解决问题.窗口加载时,值仍为0.从数据库恢复对象的状态后,绑定未更新.虽然绑定是连接的,但是当我输入数据时,数据上下文会更新.出于某种原因,当我将它设置为双向时,它就像单向一样.

更新3

我试图将代码移动到窗口加载的事件和构造函数之外,但似乎没有帮助.我发现有趣的是,在反序列化过程中不会触发PropertyChanged事件.在这种情况下,我认为它不重要,因为对象已完全恢复正常,然后我只是将它分配给数据上下文.我将数据上下文移出XAML并移入WindowLoaded,以测试XAML是否是问题.结果是一样的.

private void WindowLoaded(object sender, RoutedEventArgs e)
{
    // Restore our preferences state.
    var preferences = new UserPreferenceCommands();
    Models.UserPreferences viewModel = new Models.UserPreferences();

    // Set up the event handler before we deserialize.
    viewModel.PropertyChanged += viewModel_PropertyChanged;
    preferences.LoadPreferencesCommand.Execute(viewModel);

    // At this point, viewModel is a valid object. All properties are set correctly.
    viewModel = preferences.Results;

    // After this step, the UI still shows 0's in all of the text boxs. Even though the values are not zero.
    this.DataContext = viewModel;
}

// NEVER gets fired from within the WindowLoaded event.
void viewModel_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
    MessageBox.Show("Property changed!");
}

// This changes the model properties and is immediately reflected in the UI. Why does this not happen within the WindowLoaded event?
private void TestButtonClickEvent(object sender, RoutedEventArgs e)
{
    var context = this.DataContext as Models.UserPreferences;
    context.SelectedCollectionDevice.ComPort = 1536;
}

更新4 - 发现问题

我已经确定了问题,但仍需要一个解决方案.数据绑定的全部意义在于我不必执行此手动分配.我的INotify实现有问题吗？

private void WindowLoaded(object sender, RoutedEventArgs e)
{
    // Restore our preferences state.
    var preferences = new UserPreferenceCommands();
    Models.UserPreferences viewModel = new Models.UserPreferences();

    // Set up the event handler before we deserialize.
    viewModel.PropertyChanged += viewModel_PropertyChanged;
    preferences.LoadPreferencesCommand.Execute(viewModel);

    // At this point, viewModel is a valid object. All properties are set correctly.
    viewModel = preferences.Results;

    // After this step, the UI still shows 0's in all of the text boxs. Even though the values are not zero.
    this.DataContext = viewModel;

    // SOLUTION: - Setting the actual property causes the UI to be reflected when the window is initialized; setting the actual data context does not. Why? Also note that I set this property and my PropertyChanged event handler still does not fire.
    ((Models.UserPreferences) DataContext).SelectedCollectionDevice = viewModel.SelectedCollectionDevice;

}

Answer 1

默认情况下,TextTextBox 的属性仅在对焦点丢失时才更新.您是否使用DataContext验证了它？

如果要覆盖此行为,则必须以UpdateSourceTrigger这种方式包含该属性:

Text="{Binding Path=SelectedCollectionDevice.BaudRate, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}

将UpdateSourceTrigger值设置为PropertyChanged,当您更改绑定属性的值时,更改将反映在TextBox中,只要文本更改.

有关使用一个有用的教程UpdateSourceTrigger属性是在这里.

Answer 2

好吧,我能够确定问题并解决问题.事实证明这是导致这种情况的汇编.

首先,我的模型.

UserPreferences < - MainWindow是绑定到此的数据.

[Serializable]
public class UserPreferences : INotifyPropertyChanged
{
    private CollectionDevice selectedCollectionDevice;

    public UserPreferences()
    {
        this.AvailableCollectionDevices = new List<CollectionDevice>();

        var yuma1 = new CollectionDevice
        {
            BaudRate = 4800,
            ComPort = 31,
            DataPoints = 1,
            Name = "Trimble Yuma 1",
            WAAS = true
        };

        var yuma2 = new CollectionDevice
        {
            BaudRate = 4800,
            ComPort = 3,
            DataPoints = 1,
            Name = "Trimble Yuma 2",
            WAAS = true
        };

        var toughbook = new CollectionDevice
        {
            BaudRate = 4800,
            ComPort = 3,
            DataPoints = 1,
            Name = "Panasonic Toughbook",
            WAAS = true
        };


        var other = new CollectionDevice
        {
            BaudRate = 0,
            ComPort = 0,
            DataPoints = 0,
            Name = "Other",
            WAAS = false
        };

        this.AvailableCollectionDevices.Add(yuma1);
        this.AvailableCollectionDevices.Add(yuma2);
        this.AvailableCollectionDevices.Add(toughbook);
        this.AvailableCollectionDevices.Add(other);

        this.SelectedCollectionDevice = this.AvailableCollectionDevices.First();
    }

    /// <summary>
    /// Gets or sets the GPS collection device.
    /// </summary>
    public CollectionDevice SelectedCollectionDevice
    {
        get
        {
            return selectedCollectionDevice;
        }
        set
        {
            selectedCollectionDevice = value;

            if (selectedCollectionDevice.Name == "Other")
            {
                this.AvailableCollectionDevices[3] = value;
            }

            this.OnPropertyChanged("SelectedCollectionDevice");
        }
    }

    /// <summary>
    /// Gets or sets a collection of devices that can be used for collecting GPS data.
    /// </summary>
    [Ignore]
    [XmlIgnore]
    public List<CollectionDevice> AvailableCollectionDevices { get; set; }

    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Notifies objects registered to receive this event that a property value has changed.
    /// </summary>
    /// <param name="propertyName">The name of the property that was changed.</param>
    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

在SelectedCollectionDevice我的设置器中我不想看看所选设备是否是其他设备.所有其他设备(yuma1,panasonic等)都具有永不改变的预定属性值.当用户选择"其他"时,将显示文本框,并且他们可以手动输入数据.问题是当在窗口加载期间从数据库恢复手动输入的数据时,我没有将自定义数据分配给SelectedCollectionDevice集合中的相应对象.

在窗口加载期间,将Combobox.SelectedItem其设置为索引SelectedCollectionDevice.将Combobox.ItemsSource被设置为AvailableCollectionDevices收集.

this.CollectionDevice.SelectedIndex = 
    viewModel.AvailableCollectionDevices.IndexOf(
        viewModel.AvailableCollectionDevices.FirstOrDefault(
            acd => acd.Name == viewModel.SelectedCollectionDevice.Name));

执行上面的代码时,组合框从其数据源中提取默认对象,该数据源的所有值都设置为零.在组合框的SelectionChanged事件中,我将数据上下文分配SelectedCollectionDevice给与组合框关联的零输出项.

private void CollectionDeviceSelected(object sender, SelectionChangedEventArgs e)
{
    if (e.AddedItems.Count > 0 && e.AddedItems[0] is CollectionDevice)
    {
        // Assign the view models SelectedCollectionDevice to the device selected in the combo box.
        var device = e.AddedItems[0] as CollectionDevice;
        ((Models.UserPreferences)this.DataContext).SelectedCollectionDevice = device;

        // Check if Other is selected. If so, we have to present additional options.
        if (device.Name == "Other")
        {
            OtherCollectionDevicePanel.Visibility = Visibility.Visible;
        }
        else if (OtherCollectionDevicePanel.Visibility == Visibility.Visible)
        {
            OtherCollectionDevicePanel.Visibility = Visibility.Collapsed;
        }
    }
}

长话短说,我在setter中添加了上面的代码,SelectedCollectionDevice以便将值应用于AvailableCollectionDevicesList <>.这样,当组合框选择了"其他"值时,它会使用正确的数据从集合中提取值.在反序列化期间,我只是反序列化SelectedCollectionDevice而不是List <>这就是为什么数据在窗口第一次加载时总是被覆盖的原因.

这也解释了为什么重新分配数据上下文SelectedCollectionDevice属性与本地viewModel.SelectedCollectionDevice工作.我正在替换与组合框关联的零对象,该组合框在SelectionChanged事件期间设置了数据上下文.我无法在XAML中设置DataContext并删除手动分配.

感谢所有帮助,它帮助我缩小调试范围,直到我最终解决了问题.非常感激!