how I can get direct access of control placed in User control? - wpf

Question

I have a label under my user control. Below is the XAML code of my User Control.
<UserControl x:Class="Class_CalcProject"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:ViewModel="clr-namespace:Class_WPFCalc_Project.WPF_Calculator.ViewModelCalculator"
xmlns:local="clr-namespace:Class_WPFCalc_Project"
mc:Ignorable="d"
d:DesignHeight="315" d:DesignWidth="650"
Loaded="SetTextBoxFocus"
KeyUp="KeyBoardHelper">
<Grid>
<Label x:Name="lblHello" />
</Grid>
</User Control>
Below is the Code behind file of User Control in VB.NET:
Import System.Data
Import System.ComponentModel
Import System.Collections
Import System.Collections.ObjectModel
Class Class_CalcProject
Public Sub New()
InitializeComponent()
End Sub
End Class
I have another Class File with Name Testing.vb
Import System.Data
Import System.ComponentModel
Import System.Collections
Import System.Collections.ObjectModel
Class Class_Testing
End Class
My question is Is there any way to access my Label1 (Control) which is placed inside User Control in Testing Class? Where I can directly Change /set any property of Label1. Something similar like:
Label1.IsEnabled = True
or
UserControl.Current.Windows.OfType(Of Class_CalcProject)().First().Label1.IsEnabled = True
In norwal WPF application I can able to access my label control in Testing Class by writing and change / set its property:
Application.Current.Windows.OfType(Of Class_CalcProject)().First().Label1.IsEnabled = True
In windows WPF application the above code is working fine for me. But when I try to convert from Windows to User Control it doesn't work. As I am newbie in WPF and vb.net. Any help in this regard will be highly appreciated. Thanks in advance for posting your reply.

Answer 1

This is what Properties are for. You shouldn't be able to access those controls outside the UserControl directly. But you can.
Any Control in .Net has a property called Controls, which lists the controls immediately inside the parent. You can get them all with some recursion in an extension method:
<Extension()> _
Public Function ChildControls(Of T As Control)(ByVal parent As Control) As List(Of T)
Dim result As New List(Of Control)
For Each ctrl As Control In parent.Controls
If TypeOf ctrl Is T Then result.Add(ctrl)
result.AddRange(ctrl.ChildControls(Of T)())
Next
Return result.ToArray().Select(Of T)(Function(arg1) CType(arg1, T)).ToList()
End Function
This method returns all children controls from the parent. From here, you would need to get the control you are looking for by name. Usage:
Dim myLabel = CType(TeradiodeTestPanel1.ChildControls.Where(Function(c) c.Name = "Label1").Single(), Label)
The Single method will throw an exception if the control isn't found, so Try...Catch accordingly.

Answer 2

You need to set the DataContext class for your UserControl and bind it's various properties to properties in that DataContext class.
It is considered best practice to observe the MVVM pattern and make your ViewModel class the DataContext of your UserControl. Your Testing Class could be that VM it would just need some modifications...
It is also best practice to use Data Binding instead of accessing the control properties in code behind so instead of Label1.IsEnabled = True you'd have <Label x:Name="lblHello" IsEnabled={Binding HelloLabelEnabled}/> in your XAML and HelloLabelEnabled property in your ViewModel which implements some form of change notification...
That's how things are supposed to work in WPF... you could, in theory, continue to code all this in your code-behind but that is highly discouraged and will make your life miserable in the long run...