为什么我的自定义UserControl上的依赖项属性无法识别？

Question

I have a UserControl called BranchFilter , with the following property:

private int? _branchId;
public int? LocalBranchId
{
    get { return _branchId; }
    set
    {
        SetProperty(ref _branchId, value);
        OnBranchChanged();
    }
}

In the same control, I register a dependency property so that I can bind the branch id to a viewmodel:

public static readonly DependencyProperty BranchIdProperty = DependencyProperty.Register(nameof(LocalBranchId), typeof(int?), typeof(BranchFilter), new UIPropertyMetadata(null));

And when I try and access this property, without even binding it, in a view, like so:

<controls:BranchFilter Grid.Row="0" BranchId="0">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="BranchChanged">
            <i:InvokeCommandAction Command="{Binding LoadItems}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</controls:BranchFilter>

I get the compile errors:

The member "BranchId" is not recognized or is not accessible.

The property 'BranchId' was not found in type 'BranchFilter'.

The property 'BranchId' does not exist in XML namespace 'clr-namespace:ApptBook.Client.Modules.Common.Controls'

I have followed every example, but they're all the same, for adding the dependency property, but everything I have tried has failed. What could be wrong with something so simple?

Answer 1

Should you not be accessing it using LocalBranchId instead of BranchId ?

<controls:BranchFilter Grid.Row="0" LocalBranchId="0">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="BranchChanged">
            <i:InvokeCommandAction Command="{Binding LoadItems}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</controls:BranchFilter>

I would also rename the DependencyProperty from BranchIdProperty to LocalBranchIdProperty .

Answer 2

You should correctly declare LocalBranchId as a dependency property:

public static readonly DependencyProperty LocalBranchIdProperty =
    DependencyProperty.Register(
        nameof(LocalBranchId), typeof(int?), typeof(BranchFilter));

public int? LocalBranchId
{
    get { return (int?)GetValue(LocalBranchIdProperty); }
    set { SetValue(LocalBranchIdProperty, value); }
}

---

If you need to get notified when the property value changes, you can register a PropertyChangedCallback by PropertyMetadata:

public static readonly DependencyProperty LocalBranchIdProperty =
    DependencyProperty.Register(
        nameof(LocalBranchId), typeof(int?), typeof(BranchFilter),
        new PropertyMetadata(LocalBranchIdPropertyChanged));

public int? LocalBranchId
{
    get { return (int?)GetValue(LocalBranchIdProperty); }
    set { SetValue(LocalBranchIdProperty, value); }
}

private static void LocalBranchIdPropertyChanged(
    DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
    var control = (BranchFilter)obj;
    var id = (int?)e.NewValue;
    ...
}