从Silverlight XAML调用基类方法

Question

As part of learning Silverlight, I'm trying to create a base UserControl to use as the starting point for my inherited controls. It's very simple, it merely defines some callback methods:

public class ClickableUserControl : UserControl
{
    private Control _superParent;

    public ClickableUserControl()
    {

    }

    public ClickableUserControl(Control superParent)
    {
        _superParent = superParent;

        this.MouseEnter += new MouseEventHandler(PostfixedLayoutItem_MouseEnter);
        this.MouseLeave += new MouseEventHandler(PostfixedLayoutItem_MouseLeave);
        this.MouseLeftButtonDown += new MouseButtonEventHandler(PostfixedLayoutItem_MouseLeftButtonDown);
    }

    public virtual void PostfixedLayoutItem_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        var elements = VisualTreeHelper.FindElementsInHostCoordinates(e.GetPosition(null), this);
        if (elements.Any(elm => elm is ClickToEditTextBox))
        {
            e.Handled = false;
        }
    }

    public void PostfixedLayoutItem_MouseLeave(object sender, MouseEventArgs e)
    {
        this.Cursor = Cursors.Arrow;
    }

    public void PostfixedLayoutItem_MouseEnter(object sender, MouseEventArgs e)
    {
        this.Cursor = Cursors.Hand;
    }

    public void ClickToEditTextBox_KeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Enter || e.Key == Key.Escape)
        {
            VisualStateManager.GoToState((Control)sender, "NotEdit", false);
            _superParent.Focus();
        }
    }

}

Please note the ClickToEditTextBox_KeyDown() method which is the problem!

Now, I have an inherited control that looks as follows (CheckboxLayoutItem.xaml):

<local:ClickableUserControl x:Class="OpusFormBuilder.LayoutItems.CheckboxLayoutItem"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:OpusFormBuilder.LayoutItems"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="400" x:Name="LayoutItem">
<StackPanel Name="stackPanel1" Orientation="Horizontal">
    <lc:LayoutItem Label="layoutItem" Name="layoutItem">
                <lc:LayoutItem.LabelTemplate>
                    <DataTemplate>
                        <Self:ClickToEditTextBox KeyDown="ClickToEditTextBox_KeyDown" Text="{Binding Label, Mode=TwoWay,  ElementName=layoutItem}" MaxWidth="150" MinWidth="150" TextWrapping="Wrap" MaxHeight="200" VerticalAlignment="Top" />
                    </DataTemplate>
                </lc:LayoutItem.LabelTemplate>
                <dxe:CheckEdit Name="InnerCheckbox" Grid.ColumnSpan="2" Grid.Column="0" Grid.Row="0" VerticalAlignment="Top" HorizontalAlignment="Stretch" IsEnabled="False" />
            </lc:LayoutItem>
    <Self:ClickToEditTextBox KeyDown="ClickToEditTextBox_KeyDown" x:Name="Description" MaxWidth="150" MaxHeight="200" TextWrapping="Wrap" VerticalAlignment="Top" HorizontalAlignment="Right" />
</StackPanel>

(Note - I have removed some namespace declarations for easier reading) Note the following line:

<Self:ClickToEditTextBox KeyDown="ClickToEditTextBox_KeyDown" Text="{Binding Label, Mode=TwoWay,  ElementName=layoutItem}" MaxWidth="150" MinWidth="150" TextWrapping="Wrap" MaxHeight="200" VerticalAlignment="Top" />

in which I set the KeyDown-event on a ClickToEditTextBox (the self namespace is defined, and correctly so).

Now, in the code behind (CheckboxLayoutItem.xaml.cs) in the constructor the call to InitializeComponent() fails with the error: Failed to assign to property 'System.Windows.UIElement.KeyDown'. [Line: 17 Position: 42]

I can't debug into InitializeComponent, however, but I can't see what could possibly be the issue from this error, other than the KeyDown events in the XAML.

Now, here is my question - how come I (seemingly) cannot reference a method defined in my base-class!? Previously I had the method in the CheckboxLayoutItem.xaml.cs method itself, but as some other controls needed some of the same functionality, it seemd a better option to put it in a base class.

Cheers!

Answer 1

I know this doesn't really answer your question, but you might want to look at Template (Custom Controls) controls. UserControl really isn't the best solution for what you're trying to do here.

UserControls are best for situations where you're building a one-off control that you don't intend in inheriting from.