How can i get startX and startY position?

Question

How can i get the startX and startY position of the rectToGetXAndY. This piece of functionality is very critical to my application but it is driving me crazy. The only approach that comes to my mind is to ask the user to manually click on the top left border of the grid and then handle mouseleftbuttondown event. Obviously this is not the solution i want. Here is my code :-

<UserControl xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk"  x:Class="DelSilverlightApp.MainPage"
    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"
    mc:Ignorable="d"
    d:DesignHeight="600" d:DesignWidth="800">

    <Grid x:Name="LayoutRoot" Background="DarkSlateGray">
        <Grid x:Name="rectToGetXAndY" Background="HotPink" Width="300" Height="300" HorizontalAlignment="Center" VerticalAlignment="Center">

        </Grid>
    </Grid>
</UserControl>

EDIT :-

This the code behind :-

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace DelSilverlightApp
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
            this.Loaded += new RoutedEventHandler(MainPage_Loaded);
        }

        void MainPage_Loaded(object sender, RoutedEventArgs e)
        {
            GeneralTransform gt = rectToGetXAndY.TransformToVisual(null);
            Point p = gt.Transform(new Point(0, 0));
            MessageBox.Show(p.X + " " + p.Y);
        }
    }
}

Thanks in advance :)

Answer 1

I made it work using @AnthonyWJones' code using the following:

XAML

        <UserControl x:Class="GetPositionUi.MainPage"
            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"
            mc:Ignorable="d"
            DataContext="{Binding RelativeSource={RelativeSource Self}}"
            d:DesignHeight="300" d:DesignWidth="400">

            <Grid x:Name="LayoutRoot" Background="DarkSlateGray">
                <Grid x:Name="rectToGetXAndY" 
                        Background="HotPink" 
                        Width="300" 
                        Height="300" 
                        HorizontalAlignment="Center" 
                        VerticalAlignment="Center">
                    <TextBlock x:Name="PositionTextBlock" Text="{Binding Path=ReferencePosition}"/>
                </Grid>
            </Grid>
        </UserControl>

Code behind:

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Net;
    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Documents;
    using System.Windows.Input;
    using System.Windows.Media;
    using System.Windows.Media.Animation;
    using System.Windows.Shapes;

    namespace GetPositionUi
    {
        public partial class MainPage : UserControl
        {

            #region ReferencePosition

            /// <summary>
            /// ReferencePosition Dependency Property
            /// </summary>
            public static readonly DependencyProperty ReferencePositionProperty =
                DependencyProperty.Register("ReferencePosition", typeof(Point), typeof(MainPage),
                    new PropertyMetadata((Point)(new Point(0, 0)),
                        new PropertyChangedCallback(OnReferencePositionChanged)));

            /// <summary>
            /// Gets or sets the ReferencePosition property.  This dependency property 
            /// indicates the reference position of the child element.
            /// </summary>
            public Point ReferencePosition
            {
                get { return (Point)GetValue(ReferencePositionProperty); }
                set { SetValue(ReferencePositionProperty, value); }
            }

            /// <summary>
            /// Handles changes to the ReferencePosition property.
            /// </summary>
            private static void OnReferencePositionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
            {
                ((MainPage)d).OnReferencePositionChanged(e);
            }

            /// <summary>
            /// Provides derived classes an opportunity to handle changes to the ReferencePosition property.
            /// </summary>
            protected virtual void OnReferencePositionChanged(DependencyPropertyChangedEventArgs e)
            {
            }

            #endregion

            public MainPage()
            {
                InitializeComponent();
            }

            protected override Size ArrangeOverride(Size finalSize)
            {
                var arrangedSize = base.ArrangeOverride(finalSize);
                GeneralTransform gt = rectToGetXAndY.TransformToVisual(LayoutRoot);
                Point p = gt.Transform(new Point(0, 0));
                ReferencePosition = p;
                return arrangedSize;
            }
        }
    }

The key here is letting the base arrange the controls first, then use the transform to find the position and finally returning the new arrangedSize.

I would not recommend showing a message box at this point, but you can use the dependency property changed callback to do anything you want with the updated position.

Answer 2

In Silveright you can use this code to determine the current X and Y position of rectToGetXAndY relative to LayoutRoot:-

GeneralTransform gt = rectToGetXAndY.TransformToVisual(LayoutRoot);
Point p = gt.Transform(new Point(0, 0));