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WPF多重绑定失败。为什么?

multibinding data-binding wpf .net c#

6

Dabblernl · 技术社区 · 15 年前

我有这个标记:

   <GroupBox BorderThickness="2">
    <GroupBox.BorderBrush>
        <SolidColorBrush x:Name="Border">
            <SolidColorBrush.Color>
                <MultiBinding Converter="{StaticResource ConnectionAndLoggedInToBorderBrush}">
                    <Binding Path="IsConnected"/>
                    <Binding Path="IsLoggedIn"/>
                </MultiBinding>
            </SolidColorBrush.Color>
        </SolidColorBrush>
    </GroupBox.BorderBrush>

在后面的代码中,我在窗口加载方法中有这一行:

DataContext = uiManager;

uiManager的类型为uiManager,它有两个名为isConnected和isLoggedin的公共属性。

此代码在启动时失败,因为多绑定调用的转换器中的值数组没有填充布尔值,而是具有DependencyProperty.UnsetValue的值。

当我使用下面的标记(并更改转换器的返回类型)时,它确实有效。

   <GroupBox BorderThickness="2">
    <GroupBox.BorderBrush>
         <MultiBinding Converter="{StaticResource ConnectionAndLoggedInToBorderBrush}">
              <Binding Path="IsConnected"/>
              <Binding Path="IsLoggedIn"/>
         </MultiBinding>
    </GroupBox.BorderBrush>

在第一个示例中,通过代码隐藏中的DataContext进行的绑定集似乎失败了,但在第二个示例中有效。为什么?

对于uimanager类下面的完整性:

public class UIManager:IUIManager
    {

        #region Implementation of IUIManager

        private const string IsLoggedInProperty = "IsLoggedIn";
        private bool loggedIn;
        private readonly object loggedInLock = new object();
        public bool IsLoggedIn
        {
            get
            {
                lock (loggedInLock)
                {
                    return loggedIn;
                }
            }
            set
            {
                lock (loggedInLock)
                {
                    if(value==loggedIn)return;
                    loggedIn = value;
                    OnPropertyChanged(IsLoggedInProperty);
                }
            }
        }

        private void OnPropertyChanged(string property)
        {
            if(PropertyChanged!=null)PropertyChanged(this,new PropertyChangedEventArgs(property));
        }

        private const string IsConnectedProperty = "IsConnected";
        private bool isConnected;
        private object isConnectedLock = new object();
        public bool IsConnected
        {
            get
            {
                lock (isConnectedLock)
                {
                    return isConnected;
                }
            }
            set
            {
                lock (isConnectedLock)
                {
                    if(value==isConnected)return;
                    isConnected = value;
                    OnPropertyChanged(IsConnectedProperty);
                }
            }
        }

        #endregion

        #region Implementation of INotifyPropertyChanged

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }

编辑: 失败的xaml的转换方法(在值[0]转换为bool时失败):

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            var is_connected = (bool) values[0];
            var is_loggedin = (bool) values[1];
            return is_loggedin
                       ? is_connected
                             ? Colors.YellowGreen
                             : Colors.Red
                       : Colors.Gray;
        }

对于工作XAML:

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            var is_connected = (bool) values[0];
            var is_loggedin = (bool) values[1];
            return is_loggedin
                       ? is_connected
                             ? Brushes.YellowGreen
                             : Brushes.Red
                       : Brushes.Gray;
        }

3 回复 | 直到 14 年前

1

15

gix 15 年前

这个问题与 MultiBinding 或者你的转换器。 DependencyProperty.UnsetValue 表示绑定没有值。实际上,如果在调试模式下运行,您可以在 Output 窗口:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=IsConnected; DataItem=null; target element is 'SolidColorBrush' (HashCode=17654054); target property is 'Color' (type 'Color')
System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=IsLoggedIn; DataItem=null; target element is 'SolidColorBrush' (HashCode=17654054); target property is 'Color' (type 'Color')

因此,让我们简化标记并应用一些诊断:

<GroupBox>
    <GroupBox.BorderBrush>
        <SolidColorBrush>
            <SolidColorBrush.Color>
                <Binding Path="GroupColor" PresentationTraceSources.TraceLevel="High"/>
            </SolidColorBrush.Color>
        </SolidColorBrush>
    </GroupBox.BorderBrush>
</GroupBox>

应用附加的依赖项属性 PresentationTraceSources.TraceLevel 产生更多的输出:

System.Windows.Data Warning: 52 : Created BindingExpression (hash=17654054) for Binding (hash=44624228)
System.Windows.Data Warning: 54 :   Path: 'GroupColor'
System.Windows.Data Warning: 56 : BindingExpression (hash=17654054): Default mode resolved to OneWay
System.Windows.Data Warning: 57 : BindingExpression (hash=17654054): Default update trigger resolved to PropertyChanged
System.Windows.Data Warning: 58 : BindingExpression (hash=17654054): Attach to System.Windows.Media.SolidColorBrush.Color (hash=52727599)
System.Windows.Data Warning: 60 : BindingExpression (hash=17654054): Use Framework mentor <null>
System.Windows.Data Warning: 63 : BindingExpression (hash=17654054): Resolving source 
System.Windows.Data Warning: 65 : BindingExpression (hash=17654054): Framework mentor not found
System.Windows.Data Warning: 61 : BindingExpression (hash=17654054): Resolve source deferred
System.Windows.Data Warning: 91 : BindingExpression (hash=17654054): Got InheritanceContextChanged event from SolidColorBrush (hash=52727599)
System.Windows.Data Warning: 63 : BindingExpression (hash=17654054): Resolving source 
System.Windows.Data Warning: 66 : BindingExpression (hash=17654054): Found data context element: GroupBox (hash=51393439) (OK)
System.Windows.Data Warning: 67 : BindingExpression (hash=17654054): DataContext is null
System.Windows.Data Warning: 91 : BindingExpression (hash=17654054): Got InheritanceContextChanged event from SolidColorBrush (hash=52727599)
System.Windows.Data Warning: 63 : BindingExpression (hash=17654054): Resolving source 
System.Windows.Data Warning: 65 : BindingExpression (hash=17654054): Framework mentor not found
System.Windows.Data Warning: 63 : BindingExpression (hash=17654054): Resolving source 
System.Windows.Data Warning: 65 : BindingExpression (hash=17654054): Framework mentor not found
System.Windows.Data Warning: 63 : BindingExpression (hash=17654054): Resolving source  (last chance)
System.Windows.Data Warning: 65 : BindingExpression (hash=17654054): Framework mentor not found
System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=GroupColor; DataItem=null; target element is 'SolidColorBrush' (HashCode=52727599); target property is 'Color' (type 'Color')

我们看到装订没有找到 DataContext 绑定失败。当我更改Windows的构造函数时, 数据上下文 在初始化内容之前设置绑定工作:

public Window1()
{
    DataContext = ...;
    InitializeComponent();
}

这很奇怪,因为在其他地方绑定并不重要。不知道为什么它在那里不起作用,所以我只能提供解决办法。例如,将画笔创建为具有绑定的资源(该资源也可以是 GroupBox ):

<GroupBox BorderBrush="{DynamicResource resbrush}">
    <GroupBox.Resources>
        <SolidColorBrush x:Key="resbrush">
            <SolidColorBrush.Color>
                <MultiBinding Converter="{StaticResource ConnectionAndLoggedInToBorderBrush}">
                    <Binding Path="IsConnected"/>
                    <Binding Path="IsLoggedIn"/>
                </MultiBinding>
            </SolidColorBrush.Color>
        </SolidColorBrush>
    </GroupBox.Resources>
</GroupBox>

我建议你放下 多重装订 做一些预处理 数据上下文 如果你 UIManager 类是某种类型的 MVVM ViewModel .

2

1

agroskin 14 年前

我的理论。颜色是结构(不能为空),所以solidColorBrush.color=空是错误的。WPF无法创建solidColorBrush,您将得到异常。

 <GroupBox.BorderBrush>
     <SolidColorBrush x:Name="Border">
         <SolidColorBrush.Color>
             <MultiBinding Converter="{StaticResource 
                           ConnectionAndLoggedInToBorderBrush}">
                 <Binding Path="IsConnected"/>
                 <Binding Path="IsLoggedIn"/>
             </MultiBinding>
         </SolidColorBrush.Color>
     </SolidColorBrush>
 </GroupBox.BorderBrush>

borderBrush是对象(可以为空),所以groupBox.borderBrush=空可以。

 <GroupBox.BorderBrush>
      <MultiBinding Converter="{StaticResource 
                    ConnectionAndLoggedInToBorderBrush}">
           <Binding Path="IsConnected"/>
           <Binding Path="IsLoggedIn"/>
      </MultiBinding>
 </GroupBox.BorderBrush>

此solidColorBrush不是对象,而是工厂。它仅在需要时实例化,此时您已经附加了DataContext。

 <GroupBox.Resources>
      <SolidColorBrush x:Key="resbrush">
           <SolidColorBrush.Color>
                <MultiBinding Converter="{StaticResource 
                              ConnectionAndLoggedInToBorderBrush}">
                     <Binding Path="IsConnected"/>
                     <Binding Path="IsLoggedIn"/>
                </MultiBinding>
           </SolidColorBrush.Color>
      </SolidColorBrush>
 </GroupBox.Resources>

只有我的2美分。

读我的文章,btw,如果你需要一些奇怪的绑定或者带有奇怪转换器的动画,它可能会很有用。 http://www.codeproject.com/KB/WPF/BindingHub.aspx

3

0

Pete OHanlon 15 年前

正是因为这样的原因,您可能想考虑学习MVVM。此模式帮助您抽象模型和绑定,这样您就不必太依赖DPS了—您只需在视图模型中绑定到一个可通知属性即可。

有几篇关于MVVM的优秀文章,所以我建议你从阅读卡尔·希夫莱特、乔什·史密斯、马龙·格雷奇和萨夏·巴伯的作品开始。