Why am I seeing a "member is not recognized or is not accessible" error on my WPF User Control?

Question

I've got a custom user control with a public property that I'd like to be able to set in XAML. Here it is below.

TestControl.xaml

<UserControl x:Class="Scale.Controls.TestControl"
         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" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">

TestControl.xaml.cs

using System.Windows.Controls;

namespace MyProject.Controls
{
    public partial class TestControl : UserControl
    {
        public string TestMe { get; set; }
        public TestControl()
        {
            InitializeComponent();
        }
    }
}

Then, in my MainWindow.xaml file, I try to include this:

<controls:TestControl TestMe="asdf" />

However, even though Visual Studio autocompletes the TestMe property, I then see things with a squiggly underline that says "The member "Test Me" is not recognized or is not accessible," as seen below.

I could have sworn I've done something like this before in other projects. How can I access (i.e. set) the public properties via XAML like this?

Answer 1

Visual Studio 2017

I had exactly the same problem. It was compiling one day ... and then it wasn't. I wasn't using DependencyProperty which shouldn't be needed as above. The properties were appearing in Intellisense but gave the same message when inserted. I cleaned, built, rebuilt, restarted VS, rebooted etc. All to no avail.

Last ditch try ... I removed all the offending attributes and got a clean compile. Then I put them back and it compiled. I really wasn't expecting that. Somehow VS had gotten its knickers in a twist.

Answer 2

If you are using VS2017, try to delete bin and obj folders in all projects of your solution, clean the solution and build again. It works for me !

Answer 3

You need to declare your property as Dependency Properties

namespace MyProject.Controls
{
    public partial class TestControl : UserControl
    {
        //Register Dependency Property

        public static readonly DependencyProperty TestMeDependency = DependencyProperty.Register("MyProperty", typeof(string), typeof(TestControl));

        public string MyCar
        {
            get
            {

                return (string)GetValue(TestMeDependency);

            }
            set
            {
                SetValue(TestMeDependency, value);
            }
        }

        public TestControl()
        {
            InitializeComponent();
        }
    }
}