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WPF - Changing Focus from a RichTextBox causes a InvalidOperationException

Running into a strange issue when I have to switch focus from a RichTextBox. The xaml for my application is as follows:
<Window Name="MyWindow" x:Class="WpfBasics.MainWindow"
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"
xmlns:local="clr-namespace:WpfBasics"
mc:Ignorable="d"
Title="MainWindow" Height="600" Width="400">
<StackPanel>
<TextBlock>Box 1:</TextBlock>
<RichTextBox x:Name="Box1" TextChanged="Box1_TextChanged" />
<TextBlock>Box 2:</TextBlock>
<RichTextBox x:Name="Box2" />
</StackPanel>
</Window>
With the following codebehind (only the relevant bit):
private void Box1_TextChanged(object sender, TextChangedEventArgs e)
{
Box2.Focus();
}
The moment I use Box1, Focus throws the following exception:
System.InvalidOperationException: 'Cannot Reopen undo unit while another unit is already open.'
Looking into the CallStack I believe the issue is caused by the LostFocus event handler on a RichTextBox.

Based on the information you gave, I created a sample project that seems to work. Give this a shot:
private void Box1_TextChanged(object sender, TextChangedEventArgs e)
{
RichTextBox textBox = sender as RichTextBox;
var text = new TextRange(textBox.Document.ContentStart, textbox.Document.ContentEnd).Text;
if (IsValid(text))
{
Dispatcher.BeginInvoke((Action)ChangeFocus);
}
}
private void ChangeFocus()
{
Box2.Focus();
}
private bool IsValid(string text)
{
var plainText = text.Substring(0, text.Length - 2);
if (plainText == "hello world")
return true;
return false;
}

How do I create a textchange event for WebBrowser control in an UserControl? [duplicate]

This question already has an answer here:
How do I count number of characters into webbrowser control C#?
(1 answer)
Closed 6 years ago.
I'm using WebBrowser control to show/edit body content from an email. All of this I did in an UserControl.
I was looking for on events of designer and WebBrowser doesn't have WebBrowser.TextChange method. I'd like write on it a method to detect the number of characters that user's typing. (ONLY TEXT, ignore images, etc...)

System.Windows.Controls.WebBrowser has not text property, so it has not TextChanged event. If you really want to do this, you may try KeyDwon or KeyUp event to achieve it.
The comment can't paste long code , so i add the code here.
<UserControl x:Class="WpfApplication2.UserControl1"
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">
<Grid>
<WebBrowser Name="wb" TextInput="wb_TextInput" KeyDown="wb_KeyDown" Visibility="Visible"/>
</Grid>
</UserControl>
public partial class UserControl1 : UserControl
{
public UserControl1()
{
InitializeComponent();
//wb.Navigate("http://www.baidu.com");
wb.Navigate("http://www.bing.com");
}
private void wb_TextInput(object sender, TextCompositionEventArgs e)
{
//not work
}
private void wb_KeyDown(object sender, KeyEventArgs e)
{
MessageBox.Show(e.Key.ToString());
e.Handled = false;
}
}

How to show programmatically FocusVisualStyle?

Afters attemps I could tell that the FocusVisualStyle is only activated by the keyboard (tab and arrows keys).
Try to make the FocusVisualStyle to be applied after the component is loaded, it is impossible to do, There is an easy way to get around this problem?
I found this:
- focus visual not showing when navigating focus programically
- How do WPF buttons decide to show FocusVisualStyle?
- http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/99856840-f8ef-4547-9150-c4c46ec2f3df
But none shows a definite solution (without overwriting the component), and I could not write, can someone help?

I am not pretty sure I understand your issue, but I tried the example in one of the links and I was able to move focus to next component from code behind exactly as you would do using keyboard. Here is the code.
<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"
xmlns:local="clr-namespace:WpfApplication1" Loaded="OnLoaded"
>
<StackPanel Margin="10">
<TextBox Margin="10" x:Name="a" >A</TextBox>
<TextBox Margin="10" x:Name="b" >B</TextBox>
<Button Focusable="False" Click="OnClick">Move Focus</Button>
</StackPanel>
</Window>
public partial class MainWindow : Window {
public MainWindow() {
InitializeComponent();
}
private void OnLoaded(object sender, RoutedEventArgs e) {
a.Focus();
}
private void OnClick(object sender, RoutedEventArgs e) {
var request = new TraversalRequest(FocusNavigationDirection.Next);
var elementWithFocus = FocusManager.GetFocusedElement(FocusTest) as UIElement;
if (elementWithFocus != null)
elementWithFocus.MoveFocus(request);
}
}

Why isn't change button content working

I have this code:
private void ModifyButton_Click(object sender, RoutedEventArgs e)
{
ModifyButton.Content = "Another button name";
}
But it doesn't work. I mean, the modify button content doesn't change but the program doesn't fail or throw any exception.
I'm trying to modify the button name in order to change it's behavior (kinda Edit/Save) within the same button. Is this not possible using C#/WPF?
Thanks in advance.
EDIT:
XAML:
<Button Name="ModifyButton" Content="Modificar" Margin="5,10,0,0" Height="23" Width="120" HorizontalAlignment="Left" Click="ModifyButton_Click"></Button>
WEIRD BEHAVIOR: If I put a MessageBox.Show call after the change of the button content, then, while the message box is displayed the button dislay the new (changed) name, but after the message box is closed, then it shows it's original text.

I guess that the XAML of your UI is not bound to the value of your button. Did you check the DataBinding?
[EDIT]
Your magic information here is that you use ShowDialog(). As you already guessed, this influences your UI thread and therefore the display behavior. ShowDialog() displays the Form as a modal dialog and blocks your UI thread and therefore blocks the refresh of it. This may cause all sorts of weird behavior.

This is what i have and it works:
Window 1
<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<Grid>
<Button Name="ModifyButton" Content="Open Dialog" Margin="80,104,78,0" Height="23" Click="ModifyButton_Click" VerticalAlignment="Top"></Button>
</Grid>
</Window>
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
}
private void ModifyButton_Click(object sender, RoutedEventArgs e)
{
Window2 win2 = new Window2();
win2.ShowDialog();
}
}
Window 2
<Window x:Class="WpfApplication1.Window2"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window2" Height="300" Width="300">
<Grid>
<Button Name="ModifyButton" Content="Modificar" Margin="80,104,78,0" Height="23" Click="ModifyButton_Click" VerticalAlignment="Top"></Button>
</Grid>
</Window>
public partial class Window2 : Window
{
public Window2()
{
InitializeComponent();
}
private void ModifyButton_Click(object sender, RoutedEventArgs e)
{
ModifyButton.Content = "Another button name";
}
}

Setting control to be content of several controls

I have a control which i'm putting in dialog as a content. Due to relization of this dialog i have to create it every time when i need it(Show/Hide won't do the trick). I want my control to remember field content beetween calls. While i can apply viewmodel to achieve this i prefer just keep control as a field and assing it as content of dialog every time i need it. But i run into following error:
"Specified element is already the logical child of another element. Disconnect it first."
I tried to assing null to dialog window's content before closing it, but it doesn't solve the problem. Is there anything i can do?

Setting window.Content = null works fine for me. Following is the code I used:
public partial class MainWindow : Window
{
TextBlock textBlock = new TextBlock();
public MainWindow()
{
InitializeComponent();
}
private void Button_Click(object sender, RoutedEventArgs e)
{
TestWindow testWindow = new TestWindow();
testWindow.Content = textBlock;
testWindow.Closing += HandleTestWindowClosing;
testWindow.Show();
}
void HandleTestWindowClosing(object sender, System.ComponentModel.CancelEventArgs e)
{
var testWindow = sender as TestWindow;
if(testWindow!=null)
{
testWindow.Content = null;
testWindow.Closing -= HandleTestWindowClosing;
}
}
}

Check out the following working example. It isn't exactly your scenario, but pretty close. The key is setting the 'Child' property to null. It moves the TextBox from the top border to the bottom.
<Window x:Class="SO.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 />
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Button Grid.Row="0" Click="Move_Click">Move</Button>
<Border x:Name="topBorder" Grid.Row="1">
<TextBlock x:Name="ctrl">Some Text Block</TextBlock>
</Border>
<Border x:Name="bottomBorder" Grid.Row="2"/>
</Grid>
</Window>
and the code behind:
using System.Windows;
namespace SO
{
public partial class MainWindow :Window
{
public MainWindow( )
{
InitializeComponent( );
}
private void Move_Click( object sender, RoutedEventArgs e )
{
this.topBorder.Child = null;
this.bottomBorder.Child = this.ctrl;
}
}
}