Getting Error CS1061 on EventSetter of App.xaml

Question

I'm trying to create an element by my code and associate a style for it, also associating its EventSetter, the style works perfectly but when I try to run the function it does not work.

App.xaml

<Application x:Class="Learning.App"
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:local="clr-namespace:Learning">
<Application.Resources>
    <Style TargetType="Label" x:Key="LabelTituloEstiloPadrao">
    <Setter Property="Background" Value="White" />
    <Setter Property="HorizontalAlignment" Value="Left" />
    <Setter Property="Margin" Value="40,20,0,0" />

<EventSetter Event="MouseLeftButtonUp" Handler="lbl_MouseLeftButtonUp"/>
<EventSetter Event="MouseRightButtonUp" Handler="lbl_MouseRightButtonUp"/>

    </Style>    
    </ResourceDictionary>
</Application.Resources>
</Application>

MainWindow.xaml.cs

public ViewConfigAgendaDin()
        {
            InitializeComponent();
            ConfigInicial();

            Label l = new Label();
            lblTeste.Style = (Style)App.Current.Resources["LabelTituloEstiloPadrao"];

            StackHorarios.Children.Add(l);
        }

        private void lbl_MouseRightButtonUp(object sender, MouseButtonEventArgs e)
        {
            MessageBox.Show("Right");
        }

        public void lbl_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            MessageBox.Show("Left");
        }

when the application is being built, two errors are fired into the EventSetter

Error CS1061 "App" does not contain a setting for "lbl_MouseLeftButtonUp" and could not find any "lbl_MouseLeftButtonUp" extension method that accepts a first argument of type "App" (is there a usage directive or assembly reference missing?)

The same error also happens for the right event, how can I do to implement these two methods in my class where I am using this without giving problems?

Answer 1

Generally, you get Error CS1061 when a method is inaccessible from XAML.

Most common cases are:

• event handler is not declared in code-behind
• XAML's x:Class tag not matching the actual name of the class
• name of the method not matching the Handler of event setter
• incorrect arguments
• using a private method in the base class instead of protected
• a need for restarting the visual studio in rare cases

---

Looking at the XAML code, your class name is Learning.App

<Application x:Class="Learning.App"

But the code behind in which the event handlers are declared is ViewConfigAgendaDin

public class ViewConfigAgendaDin

You can't put the event handlers anywhere and expect the compiler to find them by itself. Because the handler is used in App.XAML, you need to Move the event handlers to App.xaml.cs and it will be good to go.

If you need them to be in ViewConfigAgendaDin class, either define the Style in ViewConfigAgendaDin.xaml or call a method in ViewConfigAgendaDin.xaml.cs from App.xaml.cs

Edit:

For example:

ViewConfigAgendaDin.xaml:

<ViewConfigAgendaDin 
    xmlns:v="clr-namespace:MY_NAMESPACE">
...
    <Label Tag="{Binding RelativeSource={RelativeSource AncestorType={x:Type v:ViewConfigAgendaDin}}}" 
           Style="{StaticResource LabelTituloEstiloPadrao}"/>
...
</ViewConfigAgendaDin>

ViewConfigAgendaDin.xaml.cs:

public void MyMethodForRightClick(object sender, MouseButtonEventArgs e)
{
    MessageBox.Show("Right");
}

App.xaml.cs:

private void lbl_MouseRightButtonUp(object sender, MouseButtonEventArgs e)
{
    ((sender as Label).Tag as ViewConfigAgendaDin).MyMethodForRightClick(sender, e);
}

---

Another way to handle this situation is to avoid code-behind altogether. Instead, make use of MVVM and Command Binding. You can easily bind any event to a command using Interactions