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How to write getters and setters to convert WPF dependency property? [duplicate]

I am trying (and failing) to do data binding on a dependency property in xaml. It works just fine when I use code behind, but not in xaml.
The user control is simply a TextBlock that bind to the dependency property:
<UserControl x:Class="WpfTest.MyControl" [...]>
<TextBlock Text="{Binding Test}" />
</UserControl>
And the dependency property is a simple string:
public static readonly DependencyProperty TestProperty
= DependencyProperty.Register("Test", typeof(string), typeof(MyControl), new PropertyMetadata("DEFAULT"));
public string Test
{
get { return (string)GetValue(TestProperty); }
set { SetValue(TestProperty, value); }
}
I have a regular property with the usual implementation of INotifyPropertyChanged in the main window.
private string _myText = "default";
public string MyText
{
get { return _myText; }
set { _myText = value; NotifyPropertyChanged(); }
}
So far so good. If I bind this property to a TextBlock on the main window everything works just fine. The text update properly if the MyText changes and all is well in the world.
<TextBlock Text="{Binding MyText}" />
However, if I do the same thing on my user control, nothing happens.
<local:MyControl x:Name="TheControl" Test="{Binding MyText}" />
And now the fun part is that if I do the very same binding in code behind it works!
TheControl.SetBinding(MyControl.TestProperty, new Binding
{
Source = DataContext,
Path = new PropertyPath("MyText"),
Mode = BindingMode.TwoWay
});
Why is it not working in xaml?

The dependency property declaration must look like this:
public static readonly DependencyProperty TestProperty =
DependencyProperty.Register(
nameof(Test),
typeof(string),
typeof(MyControl),
new PropertyMetadata("DEFAULT"));
public string Test
{
get { return (string)GetValue(TestProperty); }
set { SetValue(TestProperty, value); }
}
The binding in the UserControl's XAML must set the control instance as the source object, e.g. by setting the Bindings's RelativeSource property:
<UserControl x:Class="WpfTest.MyControl" ...>
<TextBlock Text="{Binding Test,
RelativeSource={RelativeSource AncestorType=UserControl}}"/>
</UserControl>
Also very important, never set the DataContext of a UserControl in its constructor. I'm sure there is something like
DataContext = this;
Remove it, as it effectively prevents inheriting a DataContext from the UserConrol's parent.
By setting Source = DataContext in the Binding in code behind you are explicitly setting a binding source, while in
<local:MyControl Test="{Binding MyText}" />
the binding source implicitly is the current DataContext. However, that DataContext has been set by the assignment in the UserControl's constructor to the UserControl itself, and is not the inherited DataContext (i.e. the view model instance) from the window.

I have two custom controls in my XAML, how can i bind one of the controls to another control?

I am trying to bind a Xamarin.Forms view into another custom control through XAML, where they are both presented.
XAML:
<controls:CustomThemeChanger StartImage ="{Binding StartImage}"
EndImage ="{Binding EndImage}"
x:Name = "item" />
<controls:CustomGrid TheStartText ="{Binding Text}"
CustomThemeChanger="{Binding ., Source={x:Reference item}}" />
Code behind on the 2nd grid which wants access the first view:
public CustomThemeChanger CustomThemeChanger
{
get { return (CustomThemeChanger)GetValue(CustomThemeChangerProperty); }
set { SetValue(CustomThemeChangerProperty, value); }
}
public static readonly BindableProperty CustomThemeChangerProperty = BindableProperty.Create(nameof(CustomThemeChanger), typeof(CustomThemeChanger), typeof(CustomGrid), null, BindingMode.OneWay);
Right now it is not binding anything (null). I can bind the "TheStartText" successfully, so code seems to be fine, where as the issue seems to be in the XAML where i try to get the view.

Wpf usercontrol with embedded button : change button's content

I have a simple usercontrol with a button in it which i modified.
When I add this usercontrol to my mainwindow, I can only access the usercontrol's properties. How can I access the button content ? Ideally I'd like to have a custom property let's say "TheText" and I changed it like that
<local:MyButtonControl TheText="My text here will be the button content">
This is what I have in the usercontrol "MyButtonControl"
public object TheText
{
get => (object)GetValue(_text);
set => SetValue(_text, value);
}
public static readonly DependencyProperty _text =
DependencyProperty.Register("Text", typeof(object), typeof(MyButton), new UIPropertyMetadata(null));
But what Am I supposed to put for binding ? Can't figure it out. Here's the concerned button.
<Button x:Name="button" Content="{Binding ??? }" Style="{StaticResource RoundedButton}"/>

The Binding should look like this:
<Button Content="{Binding Text,
RelativeSource={RelativeSource AncestorType=UserControl}}" .../>
Note that a correct dependency property declaration would have to use the same name for both the dependency property and the CLR wrapper. There is also a convention to name the identifier field as <PropertyName>Property.
public object Text
{
get => (object)GetValue(TextProperty);
set => SetValue(TextProperty, value);
}
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(object), typeof(MyButton));
You should certainly also use string as type of a property that is called Text. Or you call the property ButtonContent or something like that.

How to bind multiple user controls?

I have created the following User Control:
<UserControl x:Class="TextBinder" ...>
<TextBox Text="{Binding ????}" />
</UserControl>
Now I am using my user control twice in my MainWindow. The MainWindow is then bound to my ViewModel (I set the DataContext). Now the problem is: how can I bind my user controls to the user_controlViewModel?
In my ViewModel, I have created two objects let's call them UC_1 and UC_2, they contain different texts and I would like to bind them to their respective user control in my MainWindow.
What should I put at ????
Note: please do not simplify mu TextBox to double textboxes in one usercontrol. This is not what I would like since in my real life example I have more stuff than textbox only and the usercontrol should be used multiple times in one view.
Thanks!

i gave you a general answer:
within a "real(a usercontrol you wanna use with different viewmodels with different property names)" usercontrol you bind just to your own DependencyProperties and you do that with ElementName or RelativeSource binding and you should never set the DataContext within a UserControl.
<UserControl x:Name="myRealUC" x:class="MyUserControl">
<TextBox Text="{Binding ElementName=myRealUC, Path=MyOwnDPIDeclaredInMyUc, Path=TwoWay}"/>
<UserControl>
if you do that you can easily use this Usercontrol in any view like:
<myControls:MyUserControl MyOwnDPIDeclaredInMyUc="{Binding MyPropertyInMyViewmodel}"/>
and for completeness: the Dependency Property
public readonly static DependencyProperty MyOwnDPIDeclaredInMyUcProperty = DependencyProperty.Register(
"MyOwnDPIDeclaredInMyUc", typeof(string), typeof(MyUserControl), new PropertyMetadata(""));
public bool MyOwnDPIDeclaredInMyUc
{
get { return (string)GetValue(MyOwnDPIDeclaredInMyUcProperty); }
set { SetValue(MyOwnDPIDeclaredInMyUcProperty, value); }
}

Thats right, you need yo declare a dependency property in your UserControl:
public partial class TextBinder:UserControl
{
public static readonly DependencyProperty textproperty =
DependencyProperty.Register("Text", typeof(string), typeof(TextBinder));
public string Text
{
get
{
return this.GetValue(textproperty) as string;
}
set
{
this.SetValue(textproperty,value);
}
}
}
And then, you can use your usercontrol in your window at this way:
<YourNamespace:TextBinder Text={Binding ViewModelProperty}/>

Binding from DependencyProperty of a UserControl not working

I have a UserControl with one DependencyProperty which sets in codebehind (I guess this may be a source of my problem, but still don't know what to do):
UserControl
public partial class MyControl
{
public MyControl()
{
InitializeComponent();
}
public static readonly DependencyProperty TextProperty = DependencyProperty.Register("Text", typeof(string), typeof(MyControl),
new FrameworkPropertyMetadata("",FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
public string Text
{
get { return (string)GetValue(TextProperty); }
set { SetValue(TextProperty, value); InvokePropertyChanged(new PropertyChangedEventArgs("Text"));}
}
public static string GetText(DependencyObject obj)
{
return (string)obj.GetValue(TextProperty);
}
public static void SetText(DependencyObject obj, string value)
{
obj.SetValue(TextProperty, value);
}
private void ChangeText()
{
Text="some value";
}
}
In my View.xaml I use this control like this:
<MyControl Text="{Binding Text, RelativeSource={RelativeSource Self}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"/>
And the Text property in my ViewModel:
private string _text;
public string Text
{
get { return _text; }
set { _text= value; InvokePropertyChanged(new PropertyChangedEventArgs("Text"));}
}
The problem:
Text property in the ViewModel never gets updated; when use binding with a regular control like TextBox, all works perfect; if I set Text in XAML, Text propery of UserControl updates.
What I did wrong?
UPDATE
My issue was that I have set DataContext explicitly on MyControl.

Issue is in your Binding:
Text="{Binding Text, RelativeSource={RelativeSource Self},
UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
Text property is in your ViewModel but you are referring to itself by using RealtiveSource to point back to self. So, it's binding Text DP with itself.
If you have set DataContext of your control, it will automatically inherit DataContext from parent. So, you don't need RelativeSource at all.
It simply should be:
Text="{Binding Text}"
Few points more (but not related to your issue):
Since you target to use this property from within control, so go for normal DP instead of attached property.
Since at time of registration, you have set it to bind TwoWay by default. No need to explicitly do that at time of binding.
Remove InvokePropertyChanged call from your DP wrapper setter. Setter won't be called from XAML and also DP is already PropertyChanged aware.
UPDATE
In case DataContext of MyControl is set to instance of another class, above approach will search for Text property in MyControl DataContext.
You can pass DataContext of parent control (StackPanel in your case) like this:
Text="{Binding DataContext.Text, RelativeSource={RelativeSource
Mode=FindAncestor, AncestorType=StackPanel}}"

You have registered your property as attached, yet you are also using it as a regular DependencyProperty. I think that the xaml parser gets confused. Decide which one you want to use.