数据绑定到WPF中的UserControl [英] Data binding to a UserControl in WPF

问题描述

我有一个要参与数据绑定的UserControl.我已经在用户控件中设置了依赖项属性，但无法使其正常工作.

I have a UserControl that I want to participate in data binding. I've set up the dependency properties in the user control, but can't get it work.

当我用静态文本(例如BlueText ="ABC")调用时，uc显示正确的文本.当我尝试将其绑定到本地公共财产时，它总是空白.

The uc displays the correct text when I call it with static text (e.g BlueText="ABC") . When i try to bind it to a local public property, it is always blank.

<src:BlueTextBox BlueText="Feeling blue" />            <!--OK-->
<src:BlueTextBox BlueText="{Binding Path=MyString}" /> <!--UserControl always BLANK!-->
<TextBox Text="{Binding Path=MyString}" Width="100"/>  <!--Simple TextBox Binds OK-->

我将代码简化为以下简化示例.这是UserControl的XAML:

I've boiled the code down to the following simplified example. Here is the XAML of the UserControl:

    <UserControl x:Class="Binding2.BlueTextBox" ...
    <Grid>
        <TextBox x:Name="myTextBox" Text="{Binding BlueText}" Foreground="Blue" Width="100" Height="26" />
    </Grid>

以下是UserControl的代码:

Here is the code behind of the UserControl:

public partial class BlueTextBox : UserControl
{
    public BlueTextBox()
    {
        InitializeComponent(); 
        DataContext = this; // shouldn't do this - see solution
    }

    public static readonly DependencyProperty BlueTextProperty =
        DependencyProperty.Register("BlueText", typeof(string), typeof(BlueTextBox));

    public string BlueText
    {
        get { return GetValue(BlueTextProperty).ToString(); }
        set { SetValue( BlueTextProperty, value.ToString() ); }
    }

这似乎应该很简单，但我无法使其正常工作.感谢您的帮助！

This seems like it should be really easy, but I can't make it work. Thanks for your help!

更多信息:当我尝试Eugene建议的修复程序时，我注意到一些奇怪的行为.我在元数据中添加了PropertyChangedCallback；这使我可以看到BlueText设置的值.将字符串设置为静态值(="feeling blue")时，将触发PropertyChanged事件.数据绑定案例不触发PropertyChanged.我认为这意味着数据绑定值没有被发送到UserControl.(我认为在静态情况下不会调用构造函数)

More info: When i was trying the fix suggested by Eugene, I noticed some peculiar behavior. I added a PropertyChangedCallback to the metadata; this allows me to watch the value of BlueText getting set. When setting the string to a static value (="feeling blue") the PropertyChanged event fires. The data binding case does not fire PropertyChanged. I think this means the data-bound value is not getting sent to the UserControl. (I think the constructor does not get called in the static case)

解决方案::Arcturus和jpsstavares正确识别了问题.首先，在控件的构造函数中设置了DataContext = this时，我覆盖了数据绑定.这样可以防止设置数据绑定值.我还必须将控件命名为x:Name = root，并在XAML中指定Binding ElementName = root.要获得TwoWay绑定，我需要在调用方中设置Mode = TwoWay.这是正确的代码:

Solution: The problems were correctly identified by Arcturus and jpsstavares. First, I was overwriting the data binding when is set DataContext=this in the constructor of the control. This prevented the data bound value from getting set. I also had to name the control x:Name=root, and specify the Binding ElementName=root int the XAML. To get the TwoWay binding, I needed to set Mode=TwoWay in the caller. Here is the correct code:

<src:BlueTextBox BlueText="{Binding Path=MyString, Mode=TwoWay}}" /> <!--OK-->

现在在用户控件中添加了XAML:

Now the XAML in the UserControl:

    <UserControl x:Class="Binding2.BlueTextBox" x:Name="root"...
    <Grid>
        <TextBox x:Name="myTextBox" Text="{Binding ElementName=root, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
    </Grid>

最后，我在UserControl的构造函数中删除了DataContext = this.

Finally I removed the DataContext=this in the constructor of the UserControl.

    public BlueTextBox()
    {
        InitializeComponent(); 
        //DataContext = this; -- don't do this
    }

感谢大家的大力帮助！

推荐答案

您将控件中的DataContext设置为其自身，从而在其他控件中使用此控件时会覆盖DataContext.以您的情况为例:

You set the DataContext in the Control to itself, thus overwriting the DataContext when using this Control in other controls. Taking your binding as example in your situation:

<src:BlueTextBox BlueText="{Binding Path=MyString}" /> 

一旦加载并设置了所有Datacontext，由于将DataContext设置为它，它将在BlueTextBox控件中寻找MyString路径.我想这不是您打算的工作方式；).

Once loaded and all the Datacontext is set, it will look for the path MyString in your BlueTextBox thing control due to you setting the DataContext to it. I guess this is not how you intended this to work ;).

解决方案:

更改文本绑定为2个绑定之一:

Change the text binding either one of the 2 bindings:

{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type src:BlueTextBox}}, Path=BlueText}

或

命名您的控件根(或类似名称)

Name your control Root (or something like that)

<UserControl x:Name="Root"

{Binding ElementName=Root, Path=BlueText}

然后删除

DataContext = this;

来自UserControl的构造函数，它应该像超级按钮一样工作.

from the constructor of your UserControl and it should work like a charm..

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