Question

I have a usercontrol like this:

<UserControl x:Class="MySample.customtextbox"
         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="20" d:DesignWidth="300">
    <Grid>
           <TextBox x:Name="Ytextbox"  Background="Yellow"/> 
    </Grid>
</UserControl>

I want use this control in a View such as MainWindowView
How can I Binde my Ytextbox Text Property to a property in my MainWindowViewModel?

<CT:customtextbox  Text="{binding  mypropertyinviewmodel}"/>

I know that I must define a DependencyProperty for my control until I can bind a property in my viewmodel to it so i define a dependency property for my control like this:

public static readonly DependencyProperty InfoTextProperty = 
        DependencyProperty.Register("InfoText", typeof(string), typeof(customtextbox), new FrameworkPropertyMetadata(false));

public string InfoText
{
    get { return (string)GetValue(InfoTextProperty);}
    set
    {
        SetValue(InfoTextProperty, value); 
    }
} 

When I define a dependency property for my control I have a xaml error:

Error 1 Cannot create an instance of “customtextbox”.

Answer 1

new FrameworkPropertyMetadata(false)

You cannot set the default value of a string property to false (which of course is a bool).

There may be some other problems (e.g. you have no binding on the TextBox in the user coontrol declaration and you try to set a property you did not register where you create an instance) but for those you should search SO.