Develop Reference

Place a popup under a button (UWP, XAML, C#)

I have created a Button. When the button is pressed a Popup appears. The Problem is, the popup is on the top left side while the button is on the Right side.
What do I have to do in XAML to make the popup appear under the button?
I even tried to place the popup in the top rightcorner via HorizontalAllignment. The Problem then is that the popup is outside my program (Right next to it. Literally).

just use the new DropDownButton in the new winUi library, it has a build in popup which comes under the button and the button even has an arrow on right side, it is perfect for your scenario. just use the nuget package, docs are here : https://learn.microsoft.com/en-us/uwp/toolkits/winui/

You can use the Flyout which is attached to specific controls including Button, then You can use the Placement property to specify where a flyout appears: Top, Left, Bottom, Right, or Full. So you can use the Placement property to specify the flyout to appear under the button as the following code.
<Button Content="Click me">
<Button.Flyout>
<Flyout Placement="Bottom">
<TextBlock Text="This is a flyout!"/>
</Flyout>
</Button.Flyout>
</Button>
By the way, as we suggestion in the Remark part,
Do not use a Popup if a Flyout, MenuFlyout, ToolTip or ContentDialog (MessageDialog for a Windows 8 app) is more appropriate.

How to disable opening WPF popup

I have a Popup and a ToggleButton. I set a binding like this:
<ToggleButton x:Name="myToggle" Content="{Binding MyData.Title}" />
<Popup IsOpen="{Binding IsChecked, ElementName=myToggle}" >
<TextBlock Text="{Binding MyData.Details}" />
</Popup>
As you see, I bound the toggle button's content to MyData.Title and the popup's content to MyData.Details.
Now I had the criteria MyData.ShowDetails. If it is true the popup can open and if it is false the popup should not be opened.
How can I set a binding to achieve this?
I tested these bindings on the Popup but no one works:
Visibility="{Binding MyData.ShowDetails, Converter={StaticResource BooleanToVisibilityConverter}}"
IsEnable="{Binding MyData.ShowDetails}"

You could put a panel (Grid ) on top of all the content in your window.
That needs to have a background set but it can be low opacity if you still want to see the window content.
Make that visible only when the popup is shown and collapse otherwise.
Make sure you set focus to your popup when it's shown.
.
Bear in mind.
Popups are separate windows.
They are intended to be shown briefly and have a number of potential drawbacks if you show them for longer periods. EG other applications can appear under them and they don't move with their "parent" window/control.
You might find a modal window is easier and suits better, depending on your exact requirements.
Just instantiate a window and use
PopupWindow newWindow = new PopupWindow();
newWindow.ShowDialog();
Where PopupWindow is just any old window styled to look like you want the popup.
This will guarantee the user can't somehow interact with any other window in your app.
.
Another possibility is to show your "popup" content in a grid which appears on top of everything inside your main window.
That's how editing data works in this:
https://gallery.technet.microsoft.com/scriptcenter/WPF-Entity-Framework-MVVM-78cdc204
The plus or minus of that approach is that it's in the one window.
--- Brian Kress ---

I found a special answer in my case. Instead of disabling Popup, I should disable the ToggleButton:
<ToggleButton x:Name="myToggle" Content="{Binding MyData.Title}"
IsEnabled="{Binding MyData.ShowDetails}"/>
<Popup IsOpen="{Binding IsChecked, ElementName=myToggle}" >
<TextBlock Text="{Binding MyData.Details}" />
</Popup>
It works perfect!
Note: This is not a general answer for Popup. Welcome to anyone who has an answer.

WPF: Which solution? TabControl with close button and new tab button

I'm trying to find the best solution for a TabControl that both support a close button on each TabItem, and always show a "new tab button" as the last tab.
I've found some half working solutions, but i think that was for MVVM, that I'm not using. Enough to try to understand WPF =)
This is the best solution I've found so far:
http://www.codeproject.com/Articles/493538/Add-Remove-Tabs-Dynamically-in-WPF
A solution that i actually understand. But the problem is that it is using the ItemsSource, and i don't want that. I want to bind the ItemsSource to my own collection without having to have special things in that collection to handle the new tab button.
I've been search for days now but cant find a good solution.
And I'm really new to WPF, otherwise i could probably have adapted the half done solutions I've found, or make them complete. But unfortunately that is way out of my league for now.
Any help appreciated.

I have an open source library which supports MVVM and allows extra content, such as a button to be added into the tab strip. It is sports Chrome style tabs which can tear off.
http://dragablz.net

This is bit of a dirty way to achieve the Add (+) button placed next to the last TabItem without much work. You already know how to place a Delete button next to the TabItem caption so I've not included that logic here.
Basically the logic in this solution is
To bind ItemsSource property to your own collection as well as
the Add TabItem using a CompositeCollection.
Disable selection of
the Add(+) TabItem and instead perform an action to load a new tab when it
is clicked/selected.
XAML bit
<TextBlock x:Name="HiddenItemWithDataContext" Visibility="Collapsed" />
<TabControl x:Name="Tab1" SelectionChanged="Tab1_SelectionChanged" >
<TabControl.ItemsSource>
<CompositeCollection>
<CollectionContainer Collection="{Binding DataContext.MyList, Source={x:Reference HiddenItemWithDataContext}}" />
<TabItem Height="0" Width="0" />
<TabItem Header="+" x:Name="AddTabButton"/>
</CompositeCollection>
</TabControl.ItemsSource>
</TabControl>
The code behind
private void Tab1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (e.AddedItems.Contains(AddTabButton))
{
//Logic for adding a new item to the bound collection goes here.
string newItem = "Item " + (MyList.Count + 1);
MyList.Add(newItem);
e.Handled = true;
Dispatcher.BeginInvoke(new Action(() => Tab1.SelectedItem = newItem));
}
}

You could make a converter which appends the Add tab. This way the collection of tabs in you viewmodel will only contain the real tabs.
The problem is then how to know when the Add tab is selected. You could make a TabItem behavior which executes a command when the tab is selected. Incidentally I recommended this for another question just recently, so you can take the code from there: TabItem selected behavior

While I don't actually have the coded solution, I can give some insight on what is most likely the appropriate way to handle this in a WPF/MVVM pattern.
Firstly, if we break down the request it is as follows:
You have a sequence of elements that you want to display.
You want the user to be able to remove an individual element from the sequence.
You want the user to be able to add a new element to the sequence.
Additionally, since you are attempting to use a TabControl, you are also looking to get the behavior that a Selector control provides (element selection), as well as an area to display the element (content) which is selected.
So, if we stick to these behaviors you'll be fine, since the user interface controls can be customized in terms of look and feel.
Of course, the best control for this is the TabControl, which are you already trying to use. If we use this control, it satisfies the first item.
<TabControl ItemsSource="{Binding Path=Customers}" />
Afterwards, you can customize each element, in your case you want to add a Button to each element which will execute a command to remove that element from the sequence. This will satisfy the second item.
<TabControl ...>
<TabControl.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Path=CustomerId}" />
<Button Command="{Binding Path=RemoveItemCommand, Mode=OneTime,
RelativeSource={RelativeSource FindAncestor,
AncestorType={x:Type TabControl}}"
CommandParameter="{Binding}" />
</StackPanel>
</DataTemplate>
<TabControl.ItemTemplate>
</TabControl>
The last part is a bit more difficult, and will require you to actually have to create a custom control that inherits from the TabControl class, add an ICommand DependencyProperty, and customize the control template so that it not only displays the TabPanel, but right next to it also displays a Button which handles the DependencyProperty you just created (the look and feel of the button will have to be customized as well). Doing all of this will allow you to display your own version of a TabControl which has a faux TabItem, which of course is your "Add" button. This is far far far easier said than done, and I wish you luck. Just remember that the TabPanel wraps onto multiple rows and can go both horizontally or vertically. Basically, this last part is not easy at all.

Why do my TextBoxes in different tabs of a TabControl lose their undo history?

I have a TabControl with TextBox controls in the ContentTemplate. When I type some text in one tab and switch to another tab, the Undo history in the original tab is gone when I go back.
Another problem that comes up is any text that was selected is deselected and the caret moves to the beginning of the TextBox.
If I make a window with just hardcoded TabItem controls, the undo history is preserved. The issue has something to do with my binding or templates.
Here is my XAML for the main window
<Window x:Class="TabbedTextAreaTest.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>
<Grid.RowDefinitions>
<RowDefinition Height="auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
<Button Command="{Binding AddNewTab}">Add Tab</Button>
<TabControl ItemsSource="{Binding Tabs}" Grid.Row="1">
<TabControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Header}"/>
</DataTemplate>
</TabControl.ItemTemplate>
<TabControl.ContentTemplate>
<DataTemplate>
<TextBox Text="{Binding Content, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
</DataTemplate>
</TabControl.ContentTemplate>
</TabControl>
</Grid>
</Window>
Is there a way to preserve the undo/redo history and selected text when switching tabs without manually catching those commands?

When you use a TabControl which gets its tabs via databinding on ItemsSource, WPF doesn't keep the visual tree for each item around as you switch. Thus, when you switch from tab 1 to tab 2, then back to tab 1, the controls on tab 1 are not actually the same control instances which you saw on tab 1 the first time.
There are a number of ways around to deal with this - TabControls which have explicit TabItem instances do keep their visual trees when you switch tabs, so probably the easiest way to do it is to wrap your collection of tab items in something which makes TabItems for them.
Unfortunately right now I can't find a link to an example of how to do this. There are references to articles elsewhere on SO, but they all seem to point to pages which no longer exist, and I don't have time to dig any deeper.

The reason is simple. If you think the both operation you complain about are strictly UI operations: Undo: user editing on the UI control, selection: selection of the text on UI control.
When you swicth Tab to another and go back, what happens in WPF is that all controls are rebinded to there data (ModelView normally, or just Model) again, as if you was showing them for the first time. So they loose their UI appearance attributes.
To manage that correctly in Tab environment in WPF you need to manage Undo/Redo stack by your own.
Good luck.

TabControl- preventing user from changing the selected tab: MessageBox causing bug

I've been pounding away at this issue for a little while, and have only found part of the solution.
I'm trying to set up a TabControl so that I can in some cases prevent the user from changing the currently selected tab. When the user is prevented from changing the currently selected tab, then they are shown a dialog box.
I have already read the following documents:
WPF - reset ListBox scroll position when ItemsSource changes
http://wizardsofsmart.net/uncategorized/itemssourcechanged-event-using-attached-dependency-properties/
http://joshsmithonwpf.wordpress.com/2009/09/04/how-to-prevent-a-tabitem-from-being-selected/
http://social.expression.microsoft.com/Forums/en-US/wpf/thread/f7b46018-1e97-4bbe-ada8-49b75dbc1da2/
I have implemented the solution indicated in the 3rd link (though all of the above create the same error seen below). And it works, but...
Things mess up thoroughly if the user does the following:
attempts to change the tab when such an action is disallowed. The MessageBox pops up with the error.
the user clicks "OK" and is returned to the original window.
the user tries again to change the tab. No MessageBox appears.
if the user minimizes the window, and then maximizes it again, then the MessageBox that was supposed to appear earlier appears.
the user clicks "OK" and is returned to the original window... but the tab has been changed to the one they selected before, even though they should not be able to change tabs.
This is obviously not ideal behavior. Why isn't the MessageBox appearing the second time, and why is the tab changing when it should be disallowed from doing so?
If I remove the MessageBox part, it works fine.
Here is the code for the TabControl.SelectionChanged event handler:
bool _isChanging = false;
private void tabControlForNavigation_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (!_isChanging && canChangeTabs.IsChecked.HasValue)
{
_isChanging = true;
bool canLeave = canChangeTabs.IsChecked.Value; //normally this would be replaced by a check in the ViewModel
if (!canLeave)
{
int prevIndex = tabControlForNavigation.Items.IndexOf(tabControlForNavigation.SelectedContent);
tabControlForNavigation.SelectedIndex = prevIndex;
MessageBox.Show("Can't change tabs!"); //if I comment out this line, everything works fine.
}
_isChanging = false;
}
}
I am using MVVM to implement this. The Window looks like this:
<Window x:Class="TestTabControlSwitching.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>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition />
</Grid.RowDefinitions>
<CheckBox x:Name="canChangeTabs"
Content="Can Change Tabs"
IsChecked="True" />
<TabControl x:Name="tabControlForNavigation"
Grid.Row="1"
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding Collection}"
SelectedItem="{Binding SelectedItem}"
SelectionChanged="tabControlForNavigation_SelectionChanged"
Margin="4"
HorizontalAlignment="Stretch">
<TabControl.ItemTemplate>
<DataTemplate>
<ContentPresenter Content="{Binding Path=Name}" />
</DataTemplate>
</TabControl.ItemTemplate>
</TabControl>
</Grid>
I'm omitting the rest of the code for sake of brevity- there is a pretty straight-forward ViewModel structure backing the window.

As you noticed, the problem is the MessageBox inside the event handler. The focus will change to the MessageBox and you can get all kind of undesired effects. I've had my own problems with this.
Here is a couple of SO question on the same subject
WPF: Does MessageBox Break PreviewMouseDown?
Wpf stop routing event when MessageBox appear?
If you must display a message to the user then an alternate approach might be to create a new Window which you style like a MessageBox and then call Show (not ShowDialog) on it inside the event handler.

I know this post is a bit old, but I have a very easy way to accomplish this:
Use the tab_Enter event and create a method that performs your check and displays a MessageBox to the user and then set myTabs.SelectedIndex to the prior index. A simple example:
private void someTab_Enter(object sender, EventArgs e)
{
if (myCondition)
{
MessageBox.Show("Sorry, myCondition will not let you move to this tab.");
myTabs.SelectedIndex = someOtherTabIndex;
}
}

This was a very detailed question. I had the same problem you had (i.e. the message box doesn't display on 2nd or 3rd selection changed until you minimize and maximize the window) and after much debugging and multiple google searches, stumbled on the below linked MSDN forum post.
[TabControl SelectionChanged Strange Behaviour?]
Please ignore the poorly formatted question and answer. But as mentioned in the answer, putting it inside a dispatcher and focussing the selected tab after setting the index resolved the issue for me.

You are missing an easy trick. Just make focusable=False for the Tab header.
<TabItem Header="MY TAB" Focusable="False">
You could bind this property to your view model.
<TabItem Header="MY TAB" Focusable="{Binding Bool_CanHasCheeseBurger}">