AddHandler from Page1 to Show Message MainWIndow using WPF and VB.NET - wpf

Question

I'm stuck. I am trying to AddHandler for a button on Page1 such that when the button is clicked it will AddHandler to the MainWindow_MouseUp event, so I can click anywhere on the MainWindow to show a message.
How can I fix this problem?
Notes:
I have removed the Handler for MainWindow_MouseUp on MaindWindow_load event, so the message will no show on load of MainWindow.
I have a frame showing Page1.
When a button in Page1 is clicked, it's supposed to AddHandler, so MainWindow_MouseUp will show a message when MainWindow executes the MainWindow_MouseUp event.
Page1.xaml
<Page x:Class="Page1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
Title="Page1" Background="Red">
<Grid>
<Button Content="AddHandler for MainWindow MouseUp message"
Height="42"
HorizontalAlignment="Left"
Margin="0,126,0,0"
Name="Button1"
VerticalAlignment="Top"
Width="300" />
<TextBlock Height="84"
HorizontalAlignment="Left"
Margin="80,184,0,0"
Name="TextBlock1"
Text="The button will add a handler in order to show a message on the MainWindow MouseUp event"
VerticalAlignment="Top"
Width="151"
TextWrapping="Wrap" />
<TextBlock Height="23"
HorizontalAlignment="Left"
Margin="12,56,0,0"
Name="TextBlock2"
Text="Page1"
VerticalAlignment="Top" />
</Grid>
</Page>
Page1.vb
Class Page1
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs) _
Handles Button1.Click
Dim _MainWindow As New MainWindow
AddHandler _MainWindow.MouseUp, AddressOf Button1_Click
End Sub
End Class
MainWindow.xaml
<Window x:Class="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>
<Frame Source="Page1.xaml"
Height="300"
HorizontalAlignment="Left"
Margin="110,-1,0,0"
Name="Frame1"
VerticalAlignment="Top"
Width="300" />
<TextBlock Height="144"
HorizontalAlignment="Left"
Margin="0,48,0,0"
Name="TextBlock2"
Text="Click here to show a message if handler MainWindow MouseUp is added from page1"
VerticalAlignment="Top"
TextWrapping="Wrap"
Width="104"
Foreground="#FF003AFF" />
<TextBlock Height="153"
HorizontalAlignment="Left"
Margin="416,159,0,0"
Name="TextBlock3"
Text="Click here to show a message if handler MainWindow MouseUp is added from page1"
VerticalAlignment="Top"
TextWrapping="Wrap"
Foreground="#FFEF00FF" />
</Grid>
</Window>
MainWindow.vb
Public Class MainWindow
Private Sub Window_Loaded(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs) _
Handles MyBase.Loaded
RemoveHandler Me.MouseUp, AddressOf MainWindow_MouseUp
End Sub
Private Sub MainWindow_MouseUp(ByVal sender As Object, _
ByVal e As MouseEventArgs) _
Handles Me.MouseUp
Test1()
End Sub
Public Sub Test1()
MessageBox.Show("AddHandler added from page 1 was successful!")
End Sub
End Class

Answer 1

This is just all a bit confused. Let's look at what you are doing :
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
System.Windows.RoutedEventArgs) Handles Button1.Click
Dim _MainWindow As New MainWindow
AddHandler _MainWindow.MouseUp, AddressOf Button1_Click
End Sub
This is making a new MainWindow and is linking its MouseUp event to the method Button1_Click - you're telling _MainWindow to execute Page1's Button1_Click method when it fires its MouseUp event. I suspect this is not what you want to do.
Now this :
RemoveHandler Me.MouseUp, AddressOf MainWindow_MouseUp
tells me that you don't want MainWindow_MouseUp to be hooked up right away. You can get rid of this line simply by removing the Handles clause like :
Private Sub MainWindow_MouseUp(ByVal sender As Object, _
ByVal e As MouseEventArgs) 'Handles Me.MouseUp
Test1()
End Sub
Now there's nothing to remove.
So... we're back to the problem of notifying MainWindow that Page1's button has been clicked. To do this, add an event to Page1 :
Class Page1
Shared Event PageButtonClick(sender As Object, e As RoutedEventArgs)
Private Sub Button1_Click(sender As System.Object, e As _
System.Windows.RoutedEventArgs) Handles Button1.Click
RaiseEvent PageButtonClick(sender, e)
End Sub
End Class
I've made the event shared here - this allows us to link it up without creating an instance of the page in MainWindow (ie: you can simply have a frame using Page1 as source). What we're doing here is raising a PageButtonClick event in Page1 when Button1 has been clicked.
In your main window, then :
Class MainWindow
Private Sub Window_Loaded(sender As System.Object, e As _
System.Windows.RoutedEventArgs) Handles MyBase.Loaded
'Here we listen for the Page1Click event and execute the method
'Page1_Clicked when we hear it
AddHandler Page1.PageButtonClick, AddressOf Page1_Clicked
End Sub
Private Sub Window_MouseUp(sender As System.Object, e As _
System.Windows.Input.MouseButtonEventArgs)
MessageBox.Show("Hello")
End Sub
Private Sub Page1_Clicked(sender As Object, e As RoutedEventArgs)
'When we get a click from Page1, add a handler to this window's
'MouseUp event and have it execute the Sub Window_Mouseup
AddHandler Me.MouseUp, AddressOf Window_MouseUp
End Sub
End Class
Now, the above is quite dangerous because you'll always be adding handlers any time the button is clicked. You should always be very careful about adding handlers - whenever you add one you MUST make sure to remove it before freeing up whatever has hooked it up (otherwise you end up with memory leaks since handlers can root an object!). I would always do something like this (in MainWindow) :
Private _mouseUpConnected As Boolean = False
Private Sub Page1_Clicked()
If Not _mouseUpConnected Then
AddHandler Me.MouseUp, AddressOf Window_MouseUp
_mouseUpConnected = True
End If
End Sub
This makes sure you only add the handler once. Now to get rid of it later :
Private Sub Window_Closed(sender As System.Object, e As System.EventArgs) _
Handles MyBase.Closed
RemoveHandler Page1.PageButtonClick, AddressOf Page1_Clicked
if _mouseupConnected then RemoveHandler Me.MouseUp, AddressOf Window_MouseUp
End Sub
This takes care of the PageButtonClick handler - it is added when the window is loaded and removed when it is closed. It also takes care of the MouseUp handler - if it has been connected, we disconnect it before closing. This ensures that MainWindow is properly garbage collected.