How to properly bind Checkbox property

Question

I am working on a wpf application and I am dealing with checkboxes now The problem when I set the Ischecked property to "True" like this:

   <CheckBox  Visibility="{Binding checkVisibility}" IsChecked="true" 
   IsEnabled="True"></CheckBox>

I get my checkbox checked But when I try to bind a booléan property that it's value is "true" i get my checkbox always unchecked I can't see where is the proplem

this is my xaml

 <CheckBox  Visibility="{Binding checkVisibility}" IsChecked="{Binding Path=test,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" IsEnabled="True"></CheckBox>

this is my property

public bool _test = true;

public bool test {
    get {
        return _test;
    }
    set {
        if (_test == value) {
            return;
        }

        _test = value;
        RaisePropertyChanged("test");
    }
}

I want my checkbox to reflect my property value and vice versa but it's not the case as my checkbox is always unchecked I am missing something?

Edit Here is my VM:

namespace X{
public class MyViewModel :  
{ 
public MyViewModel()
{
  TestCheckbox();
}
#Region Properties

    public bool _test1 = true;
    public bool test1
    {
        get
        {
            return _test1;
        }

        set
        {
            if (_test1 == value)
            {
                return;
            }

            _test1 = value;
            RaisePropertyChanged("test1");
        }
    }

 ObservableCollection<Output> _output_List;
    public ObservableCollection<Output> output_List
    {
        get { return _output_List; }
        set
        {
            if (_output_List == value) return;
            _output_List = value;
            RaisePropertyChanged("output_List");
        }

    }
#EndRegion
#Region ButtonCommand
  private RelayCommand _SetOutputPropertiesCommand;

    public RelayCommand SetOutputPropertiesCommand => _SetOutputPropertiesCommand
                ?? (_SetOutputPropertiesCommand = new RelayCommand(
                () =>
                {   
                        foreach (Output item in output_List)
                        {
                          item.myvalue=Test2;
                        }
                    }

                }));

#EndRegion
#Region Method
  public void TestCheckbox()
    {
     Console.Writeline(Test2);
    }
#EndRegion    

            }
  public class Output
{
    public string label { get; set; }
    public string type { get; set; }
    public bool myvalue { get; set; }
    public bool Test2 { get; set; }
    [System.ComponentModel.DataAnnotations.Schema.NotMapped]
    [JsonIgnore]
    public string checkVisibility { get; set; }
}
}

My Xaml : my checkboxes are integrated in a DataGrid view

                    <DataGrid x:Name ="GridO"  Style="{x:Null}"
                    ItemsSource= "{Binding output_List,UpdateSourceTrigger=PropertyChanged}"

                  AutoGenerateColumns="False" CellStyle="{StaticResource Body_Content_DataGrid_Centering}"
                  Margin="5,0" IsReadOnly="True" SelectionMode="Single" RowHeight="50" Height="Auto">


                        <DataGrid.Columns>

                            <DataGridTextColumn Width="40*" Binding="{Binding label}">
                                <DataGridTextColumn.HeaderTemplate>
                                    <DataTemplate>
                                        <TextBlock  Text="Input"></TextBlock>
                                    </DataTemplate>
                                </DataGridTextColumn.HeaderTemplate>
                            </DataGridTextColumn>

                            <DataGridTextColumn  Width="40*" Binding="{Binding type}">
                                <DataGridTextColumn.HeaderTemplate>
                                    <DataTemplate>
                                        <TextBlock  Text = "Type"></TextBlock>
                                    </DataTemplate>
                                </DataGridTextColumn.HeaderTemplate>
                            </DataGridTextColumn>


                            <DataGridTemplateColumn Width="20*" >
                                <DataGridTemplateColumn.Header>
                                    <TextBlock Text="Value" />
                                </DataGridTemplateColumn.Header>
                                <DataGridTemplateColumn.CellTemplate>
                                    <DataTemplate>
                                            <CheckBox Margin="20,0,0,0" Visibility="{Binding checkVisibility }" IsChecked="{Binding Test2,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" IsEnabled="True"></CheckBox>
                                    </DataTemplate>
                                </DataGridTemplateColumn.CellTemplate>
                            </DataGridTemplateColumn>

                        </DataGrid.Columns>
                    </DataGrid>
   <Button x:Name="Valid_output" Cursor="Hand" Background="Transparent"  Height="55"  Width="140" Margin="0,0,20,0" Command="{Binding SetOutputPropertiesCommand}"  >

The bind is Working with "Test2" and not working with "Test1" which not in the same class as Test2 NB: the Button command(which is in the same class as "Test1") is working well

My DataTemplate: are in the App.xaml

  xmlns:v="clr-namespace:X.View"
  xmlns:vm="clr-namespace:X"
   <DataTemplate DataType="{x:Type vm:MyViewModel}">
            <v:MyWindow/>

Answer 1

I see the main problem in the DataGrid. You set ItemsSource to a collection, so for every row in the DataGrid the data source is one item in that collection. Not your MyViewModel.

This is the reason, why the Test2 is working - it is in the class which instances are in the collection.

You could try to add CheckBox to the window without DataGrid and bind the Test1 - it should work.

If you really want to use some property from your MyViewModel, you can, but it is not that easy. You have to have there something like:

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:YourNamespace"

<!--...something...-->

<DataGrid.Resources>
   <local:BindingProxy x:Key="Proxy" Data="{Binding}" />
</DataGrid.Resources>

<!--...something...-->

And then your binding in the DataGrid will look like this:

IsChecked="{Binding Data.Test1, Source={StaticResource Proxy}}"

Of course I don't know the exact settings of your application so you will have to complete/change the code according to them.

Answer 2

I suggest you to add a ViewModelBase class, like that

public abstract class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = 
    null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

Extends your ViewModel with this ViewModelBase class and implements your property

private bool myProperty;

public bool MyProperty { get; set; OnPropertyChanged(); }

Then you just have to bind on your property

<CheckBox IsChecked="{Binding MyProperty}"></CheckBox>

EDIT: To set your ViewModel as DataContext for your View you can set it from the code

MyView.DataContext = new MyViewModel();

or from the view, in the Window/User Control

<Window x:Class="MyApplication.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:MyApplication"
    Title="MainWindow" Height="350" Width="525"
    DataContext="local.MyViewModel">