WPF: Passing variables from parent xaml to usercontrol

Question

I'm trying to pass int variable from MainWindow.xaml to UserControl. When I'm debbuging myGridSize is always equal zero. I would appreciate any help.

MainWindow.xaml

x:Name="myWindow">
 <Grid>
        <my:SudokuGrid x:Name="mySudokuGrid" myGridSize="{Binding SudokuSize, ElementName=myWindow}">
        </my:SudokuGrid>
</Grid>

MainWindow code

    public static readonly DependencyProperty SudokuSizeProperty =
        DependencyProperty.Register("SudokuSize", typeof(int), typeof(MainWindow), new FrameworkPropertyMetadata(null));
    private int SudokuSize
    {
        get { return (int)GetValue(SudokuSizeProperty); }
        set { SetValue(SudokuSizeProperty, value); }
    }

    public MainWindow()
    {
        SudokuSize = 9;
        InitializeComponent();
    }

UserControl.xaml

x:Name="gridCustom">
    <UniformGrid Name="SudokuUniGrid" Style="{StaticResource CustomGridStyle}">
    </UniformGrid>

UserControl code

    public static readonly DependencyProperty myGridSizeProperty =
        DependencyProperty.Register("myGridSize", typeof(int), typeof(SudokuGrid), new FrameworkPropertyMetadata(null));

    public int myGridSize
    {
        get { return (int)GetValue(myGridSizeProperty); }
        set { SetValue(myGridSizeProperty, value); }
    }


    UniformGrid BuildGrid()
    {
        //myGridSize = 9;           
        UniformGrid theGrid = new UniformGrid();
        for (int i = 0; i < myGridSize * myGridSize; ++i)
        {
            myButton button = new myButton();
            button.cmLen = myGridSize;
            button.Width = 30;
            button.Height = 30;
            button.Tag = i;
            theGrid.Children.Add(button);            
        }
        return theGrid;
    }

    public SudokuGrid()
    {
        InitializeComponent();
        SudokuUniGrid.Children.Add(BuildGrid());
    }

Answer 1

A few issues.

Your dependency property needs to be registered to the user control type. Also you need to wait for the user control to be fully loaded before accessing.

MainWindow.xaml

<Window x:Class="WpfApplication5.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApplication5"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525"
        x:Name="myWindow">
    <Grid>
        <local:SudokuUniGrid myGridSize="{Binding SudokuSize, ElementName=myWindow}">
        </local:SudokuUniGrid>
    </Grid>
</Window>

MainWindow.xaml.cs

public partial class MainWindow : Window
{
    public static readonly DependencyProperty SudokuSizeProperty =
        DependencyProperty.Register("SudokuSize", typeof(int), typeof(MainWindow), new FrameworkPropertyMetadata(null));

    private int SudokuSize
    {
        get { return (int)GetValue(SudokuSizeProperty); }
        set { SetValue(SudokuSizeProperty, value); }
    }

    public MainWindow()
    {
        SudokuSize = 9;
        InitializeComponent();
    }
}

SudokiGrid.xaml (user control)

<UserControl x:Class="WpfApplication5.UserControl"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <UniformGrid x:Name="SudokuUniGrid">
    </UniformGrid>
</UserControl>

SudokiGrid.xaml.cs (user control)

public class SudokuUniGrid : UserControl
{
    public static readonly DependencyProperty myGridSizeProperty =
        DependencyProperty.Register("myGridSize", typeof(int), typeof(UserControl), new FrameworkPropertyMetadata(null));

    public int myGridSize
    {
        get { return (int)GetValue(myGridSizeProperty); }
        set { SetValue(myGridSizeProperty, value); }
    }

    public SudokuUniGrid()
    {
        InitializeComponent();

        Loaded += SudokuUniGrid_Loaded;
    }

    private void SudokuUniGrid_Loaded(object sender, RoutedEventArgs e)
    {
        Console.WriteLine(myGridSize);

        // build here
    }
}