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Raise a event on the User control from the Main Window in WPF

There is a textbox in my mainwindow.xaml, when I enter the textbox, I expect the label in my usercontrol, known as View1.xaml will be update accordingly. However I realise the event is not raise at all in the user control when I type the textbox, can you tell me which part is wrong?
The event is able to raise in TextBox_TextChanged_1
my MainWindow.XAML
<Window xmlns:my="http://schemas.microsoft.com/winfx/2006/xaml/presentation/ribbon"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:testapplication" x:Class="testapplication.MainWindow"
Title="MainWindow" Height="964" Width="790">
<Grid >
<Button x:Name="OpenView1" Content="Open Window 1" HorizontalAlignment="Left" Margin="33,70,0,0" VerticalAlignment="Top" Width="111" RenderTransformOrigin="0.279,1.409" Click="OpenView1_Click"/>
<Button x:Name="OpenView2" Content="Open Window 2" HorizontalAlignment="Left" Margin="33,169,0,0" VerticalAlignment="Top" Width="111" Click="OpenView2_Click"/>
<Button x:Name="OpenView3" Content="Open Window 3" HorizontalAlignment="Left" Margin="33,259,0,0" VerticalAlignment="Top" Width="111" Click="OpenView3_Click"/>
<local:View1 x:Name="ViewOne" HorizontalAlignment="Left" Margin="33,332,0,0" VerticalAlignment="Top" Height="226" Width="204" Visibility="Hidden"/>
<local:View2 x:Name="ViewTwo" HorizontalAlignment="Left" Margin="284,332,0,0" VerticalAlignment="Top" Height="226" Width="208" Visibility="Hidden"/>
<local:View3 x:Name="ViewThree" HorizontalAlignment="Left" Margin="534,332,0,0" VerticalAlignment="Top" Height="226" Width="196" Visibility="Hidden"/>
<TextBox HorizontalAlignment="Left" Height="42" Margin="326,70,0,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="182" FontSize="22" TextChanged="TextBox_TextChanged_1"/>
</Grid>
</Window>
my MainWindow.cs
namespace testapplication
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
//InitializeComponent();
}
//event handler
public event EventHandler<EventArgs> changedText;
private void OpenView1_Click(object sender, RoutedEventArgs e)
{
ViewOne.Visibility = Visibility.Visible;
}
private void OpenView2_Click(object sender, RoutedEventArgs e)
{
ViewTwo.Visibility = Visibility.Visible;
}
private void OpenView3_Click(object sender, RoutedEventArgs e)
{
ViewThree.Visibility = Visibility.Visible;
}
private void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
{
if (changedText != null)
{
changedText(this, e);
}
}
}
}
This is my UserControl, known as View1.xaml, it is included in my MainWindow.Xaml
namespace testapplication
{
/// <summary>
/// Interaction logic for View1.xaml
/// </summary>
public partial class View1 : UserControl
{
private MainWindow newWindow = new MainWindow();
public View1()
{
InitializeComponent();
newWindow.changedText += newWindow_ChangeText;
}
void newWindow_ChangeText(object sender, EventArgs e)
{
ViewOnelabel.Content = "Happy";
}
}
}
The problem is my ViewOnelabel.Content = "Happy" did not execute at all, it remain unchanged

There are a few things I would like to point out.
The equivalent of a winforms label in wpf is a TextBlock. A wpf label is actually a type of contentcontrol. Hence the content property.
In wpf there are routed events. These "bubble" up ( and tunnel down ) the visual tree. That means you can handle an event in the window from a control in a usercontrol inside it.
But mainly.
I encourage you to look into the MVVM pattern.
I've put together some code which illustrates these points.
I'd recommend just using binding and mvvm though.
My MainWindow markup:
Title="MainWindow" Height="350" Width="525"
TextBoxBase.TextChanged="Window_TextChanged"
>
<Window.DataContext>
<local:MainWindowViewModel/>
</Window.DataContext>
<Grid>
<StackPanel>
<Label Name="OutputLabel"/>
<TextBlock Text="{Binding OutputString}"/>
<local:UserControl1/>
</StackPanel>
</Grid>
Notice that it handles a textchanged event and because that's routing it will get the event from UserControl1 inside it.
Code behind:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private void Window_TextChanged(object sender, TextChangedEventArgs e)
{
OutputLabel.Content = $"Happy {((TextBox)e.OriginalSource).Text}";
}
}
You don't do anything with the text from your textbox in your handler but I have some code there proves you could get at that from mainwindow if you wanted.
My viewmodel:
public class MainWindowViewModel : INotifyPropertyChanged
{
private string inputString;
public string InputString
{
get { return inputString; }
set
{
inputString = value;
OutputString = $"{inputString.Length} characters entered";
RaisePropertyChanged();
}
}
private string outputString;
public string OutputString
{
get { return outputString; }
set
{
outputString = value;
RaisePropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Usercontrol1 just has a textbox:
<Grid>
<TextBox Text="{Binding InputString, UpdateSourceTrigger=PropertyChanged}"/>
</Grid>
As you type in that textbox, the text is transferred to the bound property in my viewmodel. That hits the code in my setter. This in turn sets OutputString which is bound to my textblock.
Text changes in both my label and textblock as I type.
Here's a link to my sample on onedrive
https://1drv.ms/u/s!AmPvL3r385QhgpgOPNKPs-veFJ2O3g

The main problem here is that your View1 class is subscribing to an event on a new MainWindow instance, not the MainWindow instance created by your application on start.
Since your MainWindow class has a reference to your View1 class (a named member "ViewOne") you should just change it from the MainWindow class.
private void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
{
ViewOne.ViewOneLabel.Content = "Happy";
}
Get rid of the chenagedText event handler and all the code in the View1.xaml.cs... you don't need it.
Note: I am hoping that you are just playing around and learning here... there is no way I would condone building a WPF application in this way.

You could only use the event of the MainPage. I recomment you to add a Property to the UserControl. In my case I call it Text.
public string Text
{
set { ViewOneLabel.Content = value; }
}
In the MainWindow use the Property within the TextChanged Event.
private void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
{
OpenView1.Text = TextBox.Text;
}

You are creating a new instance of MainWindow in your UserControl. What you want to do is to hook up an event handler to the instance that you actually see on the screen. You can get a reference to this one using the Window.GetWindow method:
public partial class View1 : UserControl
{
public View1()
{
InitializeComponent();
Loaded += (s, e) =>
{
Window mainWindow = Window.GetWindow(this) as MainWindow;
if(mainWindow != null)
mainWindow.changedText += newWindow_ChangeText;
};
}
void newWindow_ChangeText(object sender, EventArgs e)
{
ViewOnelabel.Content = "Happy";
}
}

WPF- Binding a TextBlock to a Button

The same questions has been asked many times on this site and I have read most of them. But I have a special problem (maybe?) that couldn't figure it out after hours of struggling and reading SO posts.
The problem is -simply explained, I have a WPF form which contains a Connect button. If this button is pressed a textblock must appear on that form, displaying the word "Connecting...". Upon pressing the button, some handshaking operations are done in the associated C# code which takes some time. If the program fails to connect, the textblock must change to "Failed!". Otherwise, it changes to "Succeed."
Now for this simple problem, I wrote in my XAML:
<Window x:Class="WpfTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="300" Width="200">
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Button x:Name="connecting" Content="Connect" FontWeight="Bold" Click="startConnection"
Width="60" HorizontalAlignment="Center" VerticalAlignment="Center" Grid.Row="0"/>
<TextBlock x:Name="comm_stat" Grid.Row="1" HorizontalAlignment="Center" VerticalAlignment="Center"
Text="{Binding Content}"/>
</Grid>
</Window>
And the C# code (inspired by this answer):
using System;
using System.Text;
using System.Windows;
using System.ComponentModel;
namespace WpfTest
{
public class DynamicObj : INotifyPropertyChanged
{
public DynamicObj() : this(string.Empty) { }
public DynamicObj(string txt) { Content = txt; }
private string _name;
public string Content
{
get { return _name; }
set {
_name = value;
OnPropertyChanged("Content");
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string PropertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
}
}
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = this;
comm_stat.DataContext = new DynamicObj();
}
private void startConnection(object sender, RoutedEventArgs e)
{
comm_stat.Text = "Connecting...";
bool connect2device = false;
// do the handshaking operations. the result is then assigned to connect2device
comm_stat.Text = connect2device ? "Succeed." : "Failed!";
// some other operations
}
}
}
Now the problem is, whenever I click the button, no text is appeared in the textblock. Because the program waits for the startConnection method to reach its end and then updates the bonded textblock. But I want the textblock to change right after pressing the button. How can I do this?

You can use BackgroundWorker as such:
bool connect2device = false;
private void startConnection(object sender, RoutedEventArgs e)
{
comm_stat.Text = "Connecting...";
// do the handshaking operations. the result is then assigned to connect2device
BackgroundWorker worker = new BackgroundWorker();
worker.DoWork += DoWork;
worker.RunWorkerCompleted += Completed;
worker.RunWorkerAsync();
}
private void Completed(object sender, RunWorkerCompletedEventArgs e)
{
comm_stat.Text = connect2device ? "Succeed." : "Failed!";
}
private void DoWork(object sender, DoWorkEventArgs e)
{
//Change with actual work.
Thread.Sleep(1000);
connect2device = true;
}
One side note is that you actually do not use bindings to change the text. comm_stat.Text = "Connecting..."; sets the text property directly and the DynamicObj object is not used at all. It might be good for you to read a few tutorial on MVVM.

The right way to implement Weak Event Pattern for shared property MVVM

I'm preparing an application that will have multiple objects, each one will have an integer id and string data. I want the data of the objects with the same id to be the same. I will call this object SharedObject (this object acts like a ViewModel for some database table).
One may say it is very easy. You can create a single object and reference it each time you need it. But actually this way will not work for me since I can't predict when and where the object is created.
So to handle this problem I decided to put a static event in the SharedObject class and call it when any SharedObject data is changed (like PropertyChanged event in INotifyPropertyChanged but mine is static. This will make it visible to each instance of SharedObject), but the problem is that I end up with a program full of memory leaks!!
Last night I sorted out that I had to use weak event pattern to solve the memory leak problem.
I searched the net over the last night for full implementation of weak event pattern but I ended up with nothing or deleted pages.
Finally I figured out how to do it with weak event pattern and
I created a test project to test this approach, but it did not work,
the ReceiveWeakEvent event couldn't be called.
Am I missing something?
Or what is the right way to implement this pattern?
By the way I'm using .net 4 because I need my application to support Win XP (this is what my customer needs, don't ask me about it), so I can't use the generic WeakEventManager class.
Sorry for the long post but this problem was about to make me tear my hair off, and thanks in advance.
Here is the full application code:
SharedObject class:
public class SharedObject :INotifyPropertyChanged,IWeakEventListener
{
static WaekEvent sheardEvent = new WaekEvent();
public event PropertyChangedEventHandler PropertyChanged;
public int ID { get; private set; }
public SharedObject(int id)
{
this.ID = id;
SharedWeakEventManager.AddListener(sheardEvent, this);
}
string data;
public string Data
{
get
{
return data;
}
set
{
if(value != data)
{
data = value;
OnPropertyChanged("Data");
sheardEvent.RiseSharedEvent(this, new PropertyChangedEventArgs("Data"));
}
}
}
protected virtual void OnPropertyChanged(string propName)
{
PropertyChangedEventHandler handler;
lock (this)
{
handler = PropertyChanged;
}
if (handler != null)
handler.Invoke(this, new PropertyChangedEventArgs(propName));
}
void OnSharedPropertyChaingo(object sender,PropertyChangedEventArgs e)
{
SharedObject s = sender as SharedObject;
if (s == null || s.ID != ID)
return;
data = s.Data;
OnPropertyChanged("Data");
}
public bool ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
{
if(managerType == typeof(SharedWeakEventManager) && sender is SharedObject)
{
OnSharedPropertyChaingo(sender, e as PropertyChangedEventArgs);
}
return false;
}
}
WaekEvent and SharedWeakEventManager classes:
public class SharedObject
{
public event EventHandler SharedEvent;
public void RiseSharedEvent(object sender, EventArgs args)
{
if (SharedEvent != null)
SharedEvent.Invoke(sender, args);
}
}
public class SharedWeakEventManager : WeakEventManager
{
public static SharedWeakEventManager CurrentManager
{
get
{
var manager_type = typeof(SharedWeakEventManager);
var manager = WeakEventManager.GetCurrentManager(manager_type) as SharedWeakEventManager;
if (manager == null)
{
manager = new SharedWeakEventManager();
WeakEventManager.SetCurrentManager(manager_type, manager);
}
return manager;
}
}
public static void AddListener(WaekEvent source, IWeakEventListener listener)
{
CurrentManager.ProtectedAddListener(source, listener);
}
public static void RemoveListener(WaekEvent source, IWeakEventListener listener)
{
CurrentManager.ProtectedRemoveListener(source, listener);
}
protected override void StartListening(object source)
{
((WaekEvent)source).SharedEvent += this.DeliverEvent;
}
protected override void StopListening(object source)
{
((WaekEvent)source).SharedEvent -= this.DeliverEvent;
}
}
the XAML part of the MainWindow:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<ListView x:Name="View" Margin="10,49,10,10" SelectionChanged="ListView_SelectionChanged">
<ListView.View>
<GridView>
<GridViewColumn Header="ID" Width="100" DisplayMemberBinding="{Binding ID}"/>
<GridViewColumn Header="Data" Width="100" DisplayMemberBinding="{Binding Data}"/>
</GridView>
</ListView.View>
</ListView>
<Button Content="New" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Margin="10,13.01,0,0" Click="Button_Click"/>
<TextBox x:Name="IDText" HorizontalAlignment="Left" Height="23" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="92" Margin="136.2,11,0,0"/>
<TextBox x:Name="DataText" HorizontalAlignment="Left" Height="23" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="92" Margin="280.799,11,0,0" TextChanged="DataText_TextChanged"/>
<TextBlock HorizontalAlignment="Left" TextWrapping="Wrap" Text="ID" VerticalAlignment="Top" Margin="119.593,14,0,0"/>
<TextBlock HorizontalAlignment="Left" TextWrapping="Wrap" Text="Data" VerticalAlignment="Top" Margin="251.106,15.01,0,0"/>
<Button Content="Remove" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Margin="377.799,12,0,0" Click="Button_Click_1"/>
</Grid>
MainWindow class:
public partial class MainWindow : Window
{
private ObservableCollection<SharedObject> sharedObjects;
public ObservableCollection<SharedObject> SharedObjects
{
get
{
if (sharedObjects == null)
sharedObjects = new ObservableCollection<SharedObject>();
return sharedObjects;
}
}
public SharedObject SelelectedObject { get; set; }
public MainWindow()
{
InitializeComponent();
View.ItemsSource = SharedObjects;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
int id;
if (!int.TryParse(IDText.Text, out id))
return;
SharedObject x = new SharedObject(id);
x.Data = DataText.Text;
SharedObjects.Add(x);
}
private void Button_Click_1(object sender, RoutedEventArgs e)
{
if (SelelectedObject == null)
return;
SharedObjects.Remove(SelelectedObject);
SelelectedObject = null;
}
private void DataText_TextChanged(object sender, TextChangedEventArgs e)
{
if (SelelectedObject != null)
SelelectedObject.Data = DataText.Text;
}
private void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
SelelectedObject = View.SelectedItem as SharedObject;
if (SelelectedObject == null)
return;
IDText.Text = SelelectedObject.ID.ToString();
DataText.Text = SelelectedObject.Data;
}
}

TextBlock Won't Update

I have a TextBlock (caloriesAvailableTextBlock) which I am trying to update. The Button (eatCaloriesButton) is supposed to reduce the number which the TextBlock is bound to by 100. However, the TextBlock will not update. It just remains at 2000. Any ideas what I am missing?
My xaml in HubPage.xaml:
<StackPanel>
<TextBlock TextWrapping="Wrap" Text="Calories Available:" FontSize="24"/>
<TextBlock x:Name="caloriesAvailableTextBlock" Loaded="caloriesAvailableTextBlock_Loaded" TextWrapping="Wrap" Text="{Binding}" FontSize="36"/>
<Button x:Name="eatCaloriesButton" Content="Eat 100 Calories" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" FontSize="18" Click="eatCaloriesButton_Click" FontFamily="Global User Interface"/>
</StackPanel>
My code behind in HubPage.xaml.cs:
public CalorieTracker CalorieTracker { get; set; }
private void NavigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
CalorieTracker = new CalorieTracker();
CalorieTracker.CaloriesAvailable = 2000;
}
private void eatCaloriesButton_Click(object sender, RoutedEventArgs e)
{
CalorieTracker.CaloriesAvailable -= 100;
}
private void caloriesAvailableTextBlock_Loaded(object sender, RoutedEventArgs e)
{
((TextBlock)sender).DataContext = CalorieTracker.CaloriesAvailable;
}
My CalorieTracker.cs class which holds the number which I am updating:
public class CalorieTracker : INotifyPropertyChanged
{
private int caloriesAvailable;
public int CaloriesAvailable
{
get { return caloriesAvailable; }
set { caloriesAvailable = value;
NotifyPropertyChanged("CaloriesAvailable");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
My understanding is that whenever CalorieTracker.CaloriesAvailable is changed, it will let all occurences of that variable know, but that is not what is happening. Any idea why not? Or am I just way off base?

The problem here appears to be how you set up your binding.
You set the whole DataContext to that int for your textblock. This is not what you want to do. For that to update on variable change, well, a lot of stuff would have to be different (for starters the runtime would have to listen on DataContextChanged instead of PropertyChanged).
Instead, set the DataContext for the page to your view model, then bind to a property:
<TextBlock x:Name="caloriesAvailableTextBlock" TextWrapping="Wrap" Text="{Binding CaloriesAvailable}" FontSize="36"/>
private void NavigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
DataContext = CalorieTracker = new CalorieTracker();
CalorieTracker.CaloriesAvailable = 2000;
}
Now your NotifyPropertyChanged will actually do what you expected, and your UI will update. This is a much better fit for the MVVM pattern anyways.

Simple databinding not working

I'm new to WPF and I'm trying to make a simple app, a stopwatch. It works fine if I'm not doing the data binding. Here's my XAML.
<Window x:Class="StopWatch.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:s="clr-namespace:StopWatch"
Title="MainWindow" Height="318" Width="233">
<Window.Resources>
<s:StopWatchViewModel x:Key="swViewModel" x:Name="swViewModel"></s:StopWatchViewModel>
</Window.Resources>
<Grid DataContext="{StaticResource swViewModel}">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="auto"/>
<RowDefinition Height="128*" />
</Grid.RowDefinitions>
<TextBlock Grid.Row="1" Height="49" HorizontalAlignment="Left" Margin="42,50,0,0" Name="txtTime" Text="{Binding Path=Message}" VerticalAlignment="Top" Width="147" FontSize="20" TextAlignment="Center" />
<Button Content="Start" Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="12,15,0,0" Name="startBtn" VerticalAlignment="Top" Width="58" Click="startBtn_Click" />
<Button Content="Stop" Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="76,15,0,0" Name="stopBtn" VerticalAlignment="Top" Width="58" Click="stopBtn_Click" />
<Button Content="Reset" Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="140,15,0,0" Name="resetBtn" VerticalAlignment="Top" Width="59"/>
</Grid>
and here is the code in MainWindow
public partial class MainWindow : Window
{
private StopWatchViewModel stopwatch;
public MainWindow()
{
InitializeComponent();
stopwatch = new StopWatchViewModel();
}
private void startBtn_Click(object sender, RoutedEventArgs e)
{
stopwatch.Start();
}
private void stopBtn_Click(object sender, RoutedEventArgs e)
{
stopwatch.Stop();
}
}
and here's the code in StopWatchViewModel.cs
class StopWatchViewModel : INotifyPropertyChanged
{
private DispatcherTimer timer;
private Stopwatch stopwatch;
private string message;
public event PropertyChangedEventHandler PropertyChanged;
public string Message
{
get
{
return message;
}
set
{
if (message != value)
{
message = value;
OnPropertyChanged("Message");
}
}
}
public StopWatchViewModel()
{
timer = new DispatcherTimer();
stopwatch = new Stopwatch();
timer.Tick += new EventHandler(timer_Tick);
timer.Start();
stopwatch.Reset();
}
public void Start()
{
stopwatch.Start();
}
public void Stop()
{
stopwatch.Stop();
}
private void timer_Tick(object sender, EventArgs e)
{
Message = stopwatch.Elapsed.ToString(); // Doesn't work.
// Message = "hello"; does not work too!
}
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
I don't know where I got it wrong.
EDIT: I got it working. So here's the working code for anyone's reference.
XAML, change the original to this
<Window x:Class="StopWatch.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:s="clr-namespace:StopWatch"
Title="MainWindow" Height="318" Width="233">
<Grid> // partial code
and in behind code, change the constructor based on Erno's suggestion.
public MainWindow()
{
InitializeComponent();
viewModel = new StopWatchViewModel();
this.DataContext = viewModel;
}
Thanks guys!

Your problem here is that you don't have any mechanism for letting WPF know that your property is updated. Basically you have two options here:
Make Message into a Dependancy Property.
Implement INotifyPropertyChanged so that it let's the GUI know when the message have been updated.
To make sure that you have all parts for getting INotifyPropertyChanged to work, check that you did all of this:
Define the event PropertyChanged.
Make a private NotifyPropertyChanged method to raise the event. This method should take a string parameter (name of the property) and raise the event like this : PropertyChanged(this, new PropertyChangedEventArgs(<nameofproperty>). The reason to make this method is to put the null check and invocation details in one place.
In the property setter, call NotifyPropertyChanged with the correct name (case-sensitive) of the property after the value has changed.

Just replace your Message property like this and it will work:
public string Message
{
get { return (string)GetValue(MessageProperty); }
set { SetValue(MessageProperty, value); }
}
public static readonly DependencyProperty MessageProperty =
DependencyProperty.Register("Message", typeof(string),
typeof(MainWindow), new UIPropertyMetadata(String.Empty));
EDIT after posting my solution I noticed you changed all the code into a ViewModel solution... feel free to ignore or go back to your first set of code.
In your new code you are creating TWO instances of the ViewModel, one in code and one in the resources. That is not good as you are manipulating the one in code and binding to the one in the resources(xaml)
EDIT:
change your constructor to this:
public MainWindow()
{
InitializeComponent();
stopwatch = new StopWatchViewModel();
this.DataContext = stopwatch;
}
That's all

Changes to the property won't get noticed if you don't implement INotifyPropertyChanged correctly. So you should do that first. Maybe you missed something when you did it earlier.