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Textbox event only fires the second time

question edited to provide a better explanation
I am using a treeview consisting of a stackpanel with a textblock and a textbox inside. What I would like to achieve is the total selection of the text when the textbox appears.
The textblock disappears by double-clicking or selecting an option from a context menu, giving visibility to the textbox to rename the item.
I'd like to have the selectall on the MouseLeftButtonDown on the textblock and also on click on a context menu option.
My treeview is contained in the MainWindow and, the stackpanel (with the text block and the textbox) is in a different file and I dynamically add it to the tree view depending on the user's action.
When I click on the StackPanel the first click highlights it, on double-click it opens a page and, on the MouseLeftButtonDown (and on click in a contextmenu option) I change the visibility of the textblock with the textbox and here I want the selectall() event to get fired.
I tried the following code and it only works halfway:
private void mniRename_Click(object sender, RoutedEventArgs e)
{
prevSelected.MyTextBlock.Visibility = Visibility.Collapsed;
prevSelected.MyTextBox.Visibility = Visibility.Visible;
prevSelected.MyTextBox.Focus();
if (prevSelected.MyTextBox.IsFocused)
{
prevSelected.MyTextBox.SelectAll();
}
prevSelected.MyTextBox.Text = prevSelected.MyTextBlock.Text;
}
The issue is that the SelectAll() event doesn't work on the first click while the Focus() works, then on the following clicks everything works fine.
The code is always executed in the same way.
Does anyone have any idea why this happens?

No really sure what you want to achieve. but what you describe can be achieved by the following code:
XAML
<StackPanel Orientation="Horizontal">
<TextBox x:Name="MyTextBox" LostFocus="MyTextBox_OnLostFocus" Width="100"/>
<TextBlock x:Name="MyTextBlock" Text="{Binding ElementName=MyTextBox, Path=Text}" MouseLeftButtonDown="MyTextBlock_OnMouseLeftButtonDown"/>
</StackPanel>
C#
private void MyTextBox_OnLostFocus(object sender, RoutedEventArgs e)
{
MyTextBox.Visibility = Visibility.Hidden;
MyTextBlock.Visibility = Visibility.Visible;
}
private void MyTextBlock_OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
MyTextBlock.Visibility = Visibility.Collapsed;
MyTextBox.Visibility = Visibility.Visible;
MyTextBox.Focus();
MyTextBox.SelectAll();
}

Show text when you press a button

I would like to know a way to make some text appear when you press a button.
I've already created a button and a text box:
<Button Height="25" Width="200" Click="Button_Click" Content="Press this button"/>
<TextBlock Height="50" Width="300" Margin="243,147,249,222" TextAlignment="Center" FontSize="30"/>
Also, I've created a boolean for when you press the button, I don´t know if this is necessary or not.
private void Button_Click(object sender, RoutedEventArgs e)
{
Boolean button = true;
}

Basically, like MaxB said, every control in WPF has a "Visibility" property, that you can change between Visible, Collapsed or Hidden.
Since you already have a Handle for the Button_Click event, all you need to do now is give a name to your TextBlock with the x:Name property like-so :
<TextBlock x:Name="MyTextBlock"/>
Then, in the code of your handler, you can choose which Visibility to apply to the TextBlock according to the state of your boolean.
You can access the TextBlock properties by the name you gave it in the XAML file, like-so :
this.MyTextBlock.Visibility = Visibility.Hidden, for example.

You didn't create a textbox you created a textblock. Firstly create a textbox and give it a name. Then on your Button_click method you can write NameOfTextBox.Text = "Your text";

LostFocus event of an Image isn't firing

I have an image which displays a delete button when tapped. What I need is for the delete button to disappear when the image has LostFocus.
Typically, for say a textbox I'd just use something like the following.
tb.LostFocus += tbOnLostFocus;
private void tbOnLostFocus(object sender, RoutedEventArgs e)
{
delBtn.Visibility = Visibility.Collapsed;
}
My issue is that the same code just isn't firing on an image. I vaguely remember reading somewhere a while ago that LostFocus events wont fire on an image as it isn't a focusable element. Not sure if my memory is correct as I can't find a reference to it now.
Has anyone found a suitable workaround or managed to achieve a similar result?

You can achieve this by using MenuFlyout. Once the image is tapped it will show delete button. if the pointer is tapped anywhere other than clicking on delete button it will be collapsed
<Image Source="ms-appx:///Assets/1.jpg" Tapped="Image_Tapped">
<Image.Resources>
<MenuFlyout x:Name="DeleteMenuFlyout">
<MenuFlyout.Items>
<MenuFlyoutItem x:Name="delete" Click="Delete_Click" Text="Delete" />
</MenuFlyout.Items>
</MenuFlyout>
</Image.Resources>
</Image>
//C#
private void Image_Tapped(object sender,TappedRoutedEventArgs e)
{
DeleteMenuFlyout.ShowAt(sender as FrameworkElement);
}

WPF Why button's background is blinking after press?

I created a UserControl, and added a Button inside it removing the Background and Text properties:
<Button x:Name="Button"
HorizontalAlignment="Center"
Height="40"
VerticalAlignment="Center"
Width="40"
RenderTransformOrigin="0,-2"
Margin="0,0,0,0"
BorderBrush="{x:Null}"
Click="Button_Click"
Background="{x:Null}"/>
I also hadled the Button Click event as below:
private void Button_Click(object sender, RoutedEventArgs e)
{
Button.Content = new cross();
}
The above code fills the Button content with another UserControl which is a simple cross pic.
I have placed the UserControl with the Button into a MainWindow app and after pressing Button, it starts blinking - background is fluently changing between two colours. Beside my functionality from code works good. I just don't know how to get rid of that blinking background.
Before click:
After click:

You could set Focusable="False" at your Button to achive this.
But you should read about the Focusableproperty in the MSDN to check if it's ok for you. I guess you can't focus the Buttonusing the tab key anymore. But maybe that's not a problem for you.

StackOverflowException when trying to show a ContextMenu and clicking on its parent

I've encountered a weird behavior in WPF. Even though there are quite a few ways to avoid this problem, I'm trying to better understand why it's happening:
I created a new WPF application, just added a button which has a ContextMenu:
<Grid>
<Button x:Name="btnTest" Margin="10,10,10,10"
MouseEnter="BtnTest_OnMouseEnter" MouseLeave="BtnTest_OnMouseLeave">
<Button.ContextMenu>
<ContextMenu x:Name="myContext">
<TextBlock Text="Context Menu Text"></TextBlock>
</ContextMenu>
</Button.ContextMenu>
</Button>
</Grid>
In the code behind I use MouseEnter to show the ContextMenu and MouseLeave to hide it:
private void BtnTest_OnMouseEnter(object sender, MouseEventArgs e)
{
myContext.PlacementTarget = btnTest;
myContext.Placement = PlacementMode.Bottom;
myContext.IsOpen = true;
}
private void BtnTest_OnMouseLeave(object sender, MouseEventArgs e)
{
myContext.IsOpen = false;
}
So now - I see the ContextMenu under the button when the mouse is on the button and it hides when the mouse leaves the button.
BUT when I click the button I get an exception
An unhandled exception of type 'System.StackOverflowException'
occurred in WindowsBase.dll
Question is - Why is the Mouse Click, specifically, triggering this exception? I don't have any code of mine running on the Click event, yet without clicking an exception doesn't occur...
BTW: Same will happen if I replace the Button with an Image for instance, so it doesn't seem to be caused by a specific control...

Change your XAML like this:
<Grid>
<Popup x:Name="myContext">
<TextBlock Text="Context Menu Text"></TextBlock>
</Popup>
<Button x:Name="btnTest" Margin="10,10,10,10"
MouseEnter="BtnTest_OnMouseEnter" MouseLeave="BtnTest_OnMouseLeave">
</Button>
</Grid>
I think there is a loop of this sort going on in your code:
you enter the button, the popup shows
you click, popup hides (default behavior of contextmenu)
button gets focus, popup is shown again
What happens if you set the ´StaysOpen´ property of the ContextMenu? If you then dont get this behavior anymore my suspicion is correct.