在 UserControl 中使用依赖属性的 wpf 问题 [英] wpf trouble using dependency properties in a UserControl

问题描述

I made a UserControl that is meant to be updated once every few seconds with data from a serial port. This UserControl should be very simple, consisting of a Label for a field name, and another Label containing the field value. I say that it should be simple, but it doesn't work. It does not update at all, and doesn't even display the field name.

Below is the code:

public partial class LabeledField : UserControl {

    public LabeledField() {
        InitializeComponent();
    }

    public string fieldName { 
        get { return fieldNameLabel.Content.ToString(); } 
        set { fieldNameLabel.Content = value; } 
    }

    public string fieldValue { 
        get { return (string)GetValue(fieldValueProperty); } 
        set { SetValue(fieldValueProperty, value); }
    }

    public static readonly DependencyProperty fieldValueProperty =
        DependencyProperty.Register(
            "fieldValue", 
            typeof(string), 
            typeof(LabeledField),
            new FrameworkPropertyMetadata(
                "No Data"
            )
        )
    ;
}

Here is the XAML:

<UserControl x:Class="DAS1.LabeledField" Name="LF"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<StackPanel Orientation="Horizontal">
    <Label Width="100" Height="30" Background="Gray" Name="fieldNameLabel" />
    <Label Width="100" Height="30" Background="Silver" Name="fieldValueLabel" Content="{Binding fieldValue}" />
</StackPanel>

And here is the XAML for the Window which references the UserControl. First the header:

<Window x:Class="DAS1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
xmlns:me="clr-namespace:DAS1"
Title="Window1" Height="580" Width="780">

Then the UserControl itself:

<me:LabeledField fieldName="Test" Width="200" Height="30" fieldValue="{Binding businessObjectField}"/>

If I knew of a more specific question to ask, I would--but can anyone tell me why this doesn't work?

解决方案

Turns out that in the XAML for the user control, the binding was incorrectly specified.

Originally it was:

<Label Width="100" Height="30" Name="fieldValueLabel" Content="{Binding fieldValue}" />

But I had not specified the element to which fieldValue belongs. It should be (assuming my user control is named "LF":

<Label Width="100" Height="30" Name="fieldValueLabel" Content="{Binding ElementName=LF, Path=fieldValue}" />

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