Question

我有一个分配给我的主窗口的数据上下文（UserPreferences），以及一个文本框，它在上下文中的一个数据上下文属性（CollectionDevice）内与属性双向绑定。

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，数据会在模型中更新。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，会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。问题是用户界面没有反映这一点。

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>

模型＆lt; - 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 ＆lt; - 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，但这样做也不行。

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

我也尝试将UpdateSourceTrigger设置为PropertyChanged，但似乎也无法解决问题。

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

更新2

我尝试跟随一些documentation from Microsoft并且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中并从构造函数中移出，但这似乎没有帮助。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，TextBox的Text属性仅在对焦点丢失时才会更新。您是否使用DataContext验证了它？

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

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

将UpdateSourceTrigger的值设置为PropertyChanged，当您更改绑定属性的值时，只要文本发生更改，更改就会反映在TextBox中。

有关UpdateSourceTrigger属性用法的有用教程是here。

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，我的模特。

UserPreferences ＆lt; - 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的设置器中，我不想查看所选设备是否其他。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SelectedCollectionDevice中的自定义数据分配给集合中的相应对象。

在窗口加载期间，Combobox.SelectedItem设置为SelectedCollectionDevice的索引。 Combobox.ItemsSource已设置为AvailableCollectionDevices集合。

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

执行上述代码时，组合框会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SelectedCollectionDevice分配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;
        }
    }
}

很长一段时间，我在SelectedCollectionDevice的设置器中添加了上面的代码，以将值应用于AvailableCollectionDevices列表＆lt;＆gt;。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而不是列表＆lt;＆gt;这就是为什么在首次加载窗口时数据总是被覆盖的原因。

这也解释了为什么使用本地SelectedCollectionDevice重新分配数据上下文viewModel.SelectedCollectionDevice属性的原因。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。非常感谢！

Answer 3

不是答案，但想发布适用于我的机器的代码以帮助OP ...

完整的xaml页面......

<Window x:Class="WpfApplication1.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="300" Width="300">
    <Grid>
        <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>
            <Button Click="ButtonBase_OnClick" Content="Set ComPort to 11"></Button>
        </StackPanel>
    </Grid>
</Window>

完整的代码背后......

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Windows;
using System.Xml.Serialization;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            DataContext = new UserPreferences();
        }

        private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
        {
            ((UserPreferences) DataContext).SelectedCollectionDevice.ComPort = 11;
        }

    }

    /// <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>
        [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));
            }
        }
    }

    /// <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;
        }
    }
}

Answer 4

我有同样的问题。我的问题是绑定属性名称错了。如果查看输出窗口，可以在运行时看到所有绑定错误。

System.Windows.Data错误：40：BindingExpression路径错误：＆＃39; SelectedProtectedWebsiteTemplate＆＃39;在＆＃39; object＆＃39;上找不到的属性＆＃39;＆＃39; ProtectedWebsitesViewModel＆＃39; （的HashCode = 32764015）＆＃39 ;. BindingExpression：路径= SelectedProtectedWebsiteTemplate.Name; 的DataItem =＆＃39; ProtectedWebsitesViewModel＆＃39; （的HashCode = 32764015）;目标元素是＆＃39; TextBox＆＃39; （名称=＆＃39;＆＃39）;目标属性是＆＃39; Text＆＃39; （类型＆＃39;字符串＆＃39）

WPF双向绑定无法正常工作

4 个答案: