Develop Reference

XAML WPF CheckBox Validation

I have a list of CheckBox'es. I would like the user to select at least one before click the next button.
I would want the Button to remain Enabled, but use a TextBlock below the CheckBox to show the prompt to select at least one CheckBox.
How can I check that.
Code:
XAML
<CheckBox x:Name="CheckBox1" Content="CheckBox1" />
<CheckBox x:Name="CheckBox2" Content="CheckBox2" />
<CheckBox x:Name="CheckBox3" Content="CheckBox3" />
<CheckBox x:Name="CheckBox4" Content="CheckBox4" />
<Button x:Name="NextButton" Click="NextButton_Click"/>
Code Behind
private void NextButton_Click(object sender, RoutedEventArgs e) {
if (CheckBox1.IsChecked ?? false) {
// do something
}
// same for other checkBoxes
}

private void NextButton_Click(object sender, RoutedEventArgs e)
{
if (!CheckBox1.IsChecked && !CheckBox2.IsChecked && !CheckBox3.IsChecked && !CheckBox4.IsChecked)
{
// update TextBlock to alert the user
}
else
{
if (CheckBox1.IsChecked)
{
// do something
}
// same for other checkboxes
}
}

You can also do the following, based on the example of just one CheckBox:
XAML
<CheckBox x:Name="CheckBox1" Content="CheckBox1" Checked="CheckBox1_OnChecked"/>
// after all your CheckBoxes insert TextBlock below
// which is Visible by default (but invisible once any CheckBox is checked)
<TextBlock x:Name="TextBlock" Visibility="Visible" Text="Please, select at least 1 checkbox"/>
<Button x:Name="NextButton" Click="NextButton_Click" Height="Auto" Width="Auto" Content="Button"/>
Code Behind
private void NextButton_Click(object sender, RoutedEventArgs e)
{
// your code
}
// We make Visibility of TextBox hidden
// Think for yourself how to take into account
// several CheckBoxes checked vs unchecked
private void CheckBox1_OnChecked(object sender, RoutedEventArgs e)
{
TextBlock.Visibility = Visibility.Hidden;
}
Think for yourself how to take into account several CheckBoxes checked vs unchecked, you may also use CheckBoxes event handler for Unchecked event: Unchecked="CheckBox1_OnUnchecked"

How to Get Tapped Item from Tapped Event in StackPanel

I have a ListPicker in an application page, but the SelectionChanged event gets called multiple times as the page loads. To avoid this, I have been following a previous question I asked here ListPicker SelectionChanged Event Called Multiple Times During Navigation in which the suggestion was instead of making ThemeListPicker_SelectionChanged make a parent stackpanel inside the datatemplate..', create a tap event in the StackPanel called stk_Tap, and 'use this tap stk_Tap to do your action as, this event would also get called every time the selection changed gets called but, it wont exhibit the buggy behavior like that of selection changed event'
Now I have adjusted my solution accordingly, but I do not know how to determine which item of the ListPicker is being selected or is currently selected. Also I removed the ListPicker SelectionChanged event in the ListPicker because I thought the StackPanel could get the item, but I am not sure if this is correct or how to do this?
XAML
<phone:PhoneApplicationPage.Resources>
<DataTemplate x:Name="PickerItemTemplate">
<TextBlock Text="{Binding Name}"/>
</DataTemplate>
</phone:PhoneApplicationPage.Resources>
<toolkit:ListPicker x:Name="ThemeListPicker" Header="Theme"
ItemTemplate="{StaticResource PickerItemTemplate}"
SelectionChanged="ThemeListPicker_SelectionChanged"/>
XAML.CS
private void ThemeListPicker_SelectionChanged(object sender,
SelectionChangedEventArgs e)
{
if(ThemeListPicker.SelectedIndex != -1)
{
var theme = (sender as ListPicker).SelectedItem;
if (index == 0)
{
Settings.LightTheme.Value = true;
MessageBox.Show("light");
}
else
{
Settings.LightTheme.Value = false;
MessageBox.Show("dark");
}
}
}
*EDIT: How I updated my solution
<phone:PhoneApplicationPage.Resources>
<DataTemplate x:Name="PickerItemTemplate">
<StackPanel tap="stk_Tap">
<TextBlock Text="{Binding Name}"/>
</StackPanel>
</DataTemplate>
</phone:PhoneApplicationPage.Resources>
<toolkit:ListPicker x:Name="ThemeListPicker" Header="Theme"
ItemTemplate="{StaticResource PickerItemTemplate}"
/>
So, even when I left the ListPicker SelectionChanged event in the code behind after making the modifications, I did not see the event being called twice upon the page loading/navigating to, but I am not sure how to get the currently selected item now?
EDIT2**
protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
themeList = new List<TestApp.Common.Theme>();
themeList.Add(new TestApp.Common.Theme() { Name = "Darker", name = "dark" });
themeList.Add(new TestApp.Common.Theme() { Name = "Lighter", name = "light" });
ThemeListPicker.ItemsSource = themeList;
}
private void stk_Tap(object sender, System.Windows.Input.GestureEventArgs e)
{
if (ThemeListPicker.SelectedIndex != -1)
{
//Need to get the current ThemeListPicker's 'name'
var selectedItem1 = (sender as StackPanel).DataContext as ListPicker;
//use selectedItem1
}
}

No need to extra tap event for such kind of work.
private void ThemeListPicker_SelectionChanged(object sender,
SelectionChangedEventArgs e)
{
if(ThemeListPicker.SelectedIndex==-1)
return;
var theme = (sender as ListPicker).SelectedItem;
if (index == 0)
{
Settings.LightTheme.Value = true;
MessageBox.Show("light");
}
else
{
Settings.LightTheme.Value = false;
MessageBox.Show("dark");
}
ThemeListPicker.SelectedIndex=-1
}
ListPicker SelectionChanged Event Called Multiple Times During Navigation
for above problem if i guess right you set listpicker's itemssource on OnNavigatedTo event. so modify you r onNavigatedTo method with
protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
if (e.NavigationMode != NavigationMode.Back)
{
// Your code goes here
}
}
//Stack panel tap event
private void stack_Tap(object sender, System.Windows.Input.GestureEventArgs e)
{
var selectedIrem = (Cast as your type)(sender as StackPanel).DataContext;
}

How to set focus to a bound ListboxItem by pressing its child element?

I am developping a small WPF application which consist mostly in displaying ObservableCollection<> in others ObservableCollection<>, and so on.
Here is a code example of what my application looks like:
<Listbox Name="MainList" ItemsSource={Binding}>
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<Textblock Text={Binding MainName} />
<Button>Add item</Button>
<Button>Delete item</Button>
<Listbox Name="ChildList" ItemsSource="{Binding Path=ChildItem}">
<ListBox.ItemTemplate>
<DataTemplate>
<Textblock Text={Binding ChildName} />
</DataTemplate>
</ListBox.ItemTemplate>
</Listbox>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</Listbox>
And visually it pretty much looks like this:
EDIT:
I will re-explain what I am trying to do.
Whenever I click Button A or Button B I want to Select the MainList ListBoxItem in which they are contained (i.e: A Item)
And in a second time whenever I click Button B:
I want to be sure that a ListBoxItem is selected in ChildList(Second Listbox in the picture)
And if so, I want to delete it in code-behind.
But my main problem is since everything is generated by my bindings I cannot get, so far, an element from my ChildList because ChildList is duplicated in any of my MainList ListBoxItem.

If I understand well the problem is that you want first click on a button of unselected item to select the MainItem, and on next click, when MainItem is already selected, preform click action. Try this when button is clicked:
private ListBoxItem FindItemContainer(DependencyObject obj)
{
while (obj != null && !(obj is ListBoxItem))
{
obj = VisualTreeHelper.GetParent(obj);
}
if (obj != null)
return obj as ListBoxItem;
else
return null;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
var lbi = FindItemContainer(sender as DependencyObject);
if (lbi != null)
{
if (lbi.IsSelected)
{
//do click event
}
else
lbi.IsSelected = true;
}
}
Of course you can also do it more MVVM way by binding ListBoxItem.IsSelected to lets say bool MainItem.MyItemIsSelected
<ListBox.ItemContainerStyle>
<Style TargetType="{x:Type ListBoxItem}">
<Setter Property="IsSelected" Value="{Binding Path=MyItemIsSelected, Mode=TwoWay}"/>
</Style>
</ListBox.ItemContainerStyle>
and Button.Command to your ICommand MainItem.DeleteCommand and then when command is executed do something like that:
if (MyItemIsSelected)
{
//do command body
}
else
MyItemIsSelected = true;
which will be better long term because you could replicate SelectedItem behaviour in ChildList object (add MyItemIsSelected and bind it to inner 'ListBoxItem.IsSelected, like discribed above) and add MySelectedItem property to ChildList:
ChildItem MySelectedItem
{
get
{
return Items.FirstOrDefault(n=>n.MyItemIsSelected);
}
}
and your delete command would look like this:
if (MyItemIsSelected)
{
ChildItem selItem = ChildItems.MySelectedItem;
if (selItem != null) ChildItems.Items.Remove(selItem);
}
else
MyItemIsSelected = true;
if everything is data bound and lists are ObservableCollections then you can do all that in object and UI will follow. Actually you can do only this child selection binding bit and still use first solution and in Button_Click look like this:
private void Button_Click(object sender, RoutedEventArgs e)
{
var lbi = FindItemContainer(sender as DependencyObject);
if (lbi != null)
{
if (lbi.IsSelected)
{
MainItem mainItem = lbi.Content as MainItem;
ChildItem selChild = mainItem.ChildItems.MySelectedItem;
if (selChild != null) mainItem.ChildItems.Items.Remove(selChild);
}
else
lbi.IsSelected = true;
}
}
Here is simple, working example on Dropbox

You can do everything you want to do in code behind:
Find the item on which the Button is pressed: in the click-event, cast the sender parameter to type Button. Its DataContext property will contain the item you want to select.
Select the item: set MainList.SelectedItem to the item.
Focus will be on the Button, but that should be ok, since it is inside the item.
Find the selected item in second listbox: locating the ListBox in the DataTemplate is tricky, but you could set its IsSynchronizedWithCurrentItem property to True, and then use the underlying child collection's default CollectionView. You'd find the current item of MainList like above. Then you'd use:
itemToDelete = CollectionViewSource.GetDefaultView(item.ChildItems).CurrentItem;
item.ChildItems.Remove(itemToDelete);

What is the correct way to code the nested methods?

I have created a registration form in silverlight 4, where i have a large number of text-boxes, in front of each text box i have placed a text-block as a required field validator, when any of the textbox left empty while loosing focus, the textblock placed in front of it must become red.
textboxes named textbox1, textbox2 ... and so as the textblocks
the problem is, i do not want code the specific method for each specific textbox, all i want to do is to complete such in just two three methods
here i did some coding which doesn't seems to be correct
private void textBox_LostFocus(object sender, RoutedEventArgs e)
{
var textBox = (TextBox) sender;
if (textbox.Text == "")
{
var textblock = "textblock" + textBox.Name.Remove(0,7);
TextblockColorChange(textblock);
}
}
private void TextblockColorChange(object sender)
{
var textblock = (TextBlock) sender;
textblock.Foreground= new SolidColorBrush(Colors.Red);
}
please suggest some better way to do so..

I'd create a UserControl that contains the TextBlock and the TextBox and use this UserControl everywhere you currently have the TextBlock and TextBox combination. Then this Usercontrol would have the LostFocus logic inside it and update the TextBlock appropriately. This prevents the need to figure out the right name of the control to update.

you need something like this,
XAML part:
<Grid x:Name="LayoutRoot" Background="White">
<StackPanel Orientation="Horizontal" Height="25">
<TextBox Width="150" LostFocus="TextBox_LostFocus"/>
<TextBlock Text="*" Foreground="#FF0000" VerticalAlignment="Center" Margin="10,0,0,0" Visibility="Collapsed"/>
</StackPanel>
</Grid>
C# Part:
private void TextBox_LostFocus(object sender, RoutedEventArgs e)
{
var textbox = sender as TextBox;
if(textbox == null) return;
var stackPanel = textbox.Parent as StackPanel;
if(stackPanel == null) return;
var textBlock = stackPanel.Children.Where(a => a is TextBlock).FirstOrDefault();
if (textBlock == null) return;
if (string.IsNullOrEmpty(textbox.Text)) textBlock.Visibility = Visibility.Visible;
else textBlock.Visibility = Visibility.Collapsed;
}

Whilst I actually prefer Bills approach (although I'd be inclined to use a Templated Control) here is another alternative which is quite fun. In your xaml use this sort of markup:-
<TextBlock Text="Enter Value 1" Foreground="{Binding Tag, ElementName=textBox1, TargetNullValue=Black}" />
<TextBox x:Name="textBox1" LostFocus="txt_LostFocus" />
Your common txt_LostFocus can look like this:-
private void txt_LostFocus(object sender, RoutedEventArgs e)
{
TextBox txt = ((TextBox)sender);
if (String.IsNullOrEmpty(txt.Text))
{
txt.Tag = new SolidColorBrush(Colors.Red);
}
else
{
txt.Tag = null;
}
}

var textblock = "textblock" + textBox.Name.Remove(0,7);
TextblockColorChange(textblock);
This code above will just send a string to TextblockColorChange()
You don't show any other code, but I'm guessing you want to do a FindControl or FindControl like search on that string before passing the result to your code.

How do I know that a Silverlight control has been displayed?

I have a list box displaying the names of help topics which can be added to and the names of the topics changed. Originally it was just displaying strings, but to get the inline editing working I changed it to use a custom type consisting of a string and an InEdit property so the UI can determine whether to display the TextBlock or TextBox:
XAML:
<ListBox ItemsSource="{Binding HelpTopics, Mode=TwoWay}"
SelectedValuePath="Description"
SelectedValue="{Binding SelectedPageId, Mode=TwoWay}"
SelectionChanged="ListBox_SelectionChanged">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock Text="{Binding Description, Mode=TwoWay}"
VerticalAlignment="Center"
MouseLeftButtonUp="TopicTextBlock_MouseLeftButtonUp"
Visibility="{Binding InEdit, Converter={StaticResource boolToVisibilityConverter}, ConverterParameter=contra}"/>
<TextBox Text="{Binding Description, Mode=TwoWay}"
Visibility="{Binding InEdit, Converter={StaticResource boolToVisibilityConverter}, ConverterParameter=pro}"
LostFocus="EditTopicTextBox_LostFocus"
HorizontalAlignment="Stretch" VerticalAlignment="Center"/>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Button Margin="5" Content="Add Topic" Command="{Binding AddTopicCommand}"/>
HelpTopics is an ObservableCollection<EditableHelpTopic>.
SelectedPageId is a string.
boolToVisibilityConverter is a converter that does what it says.
What works:
Adding a topic creates a new item and adds it to the list and put the item in to edit mode.
Double clicking on an existing item puts that item into edit mode sets the focus to the TextBox and selects all the text so it can be overwritten.
When the TextBox loses focus the edit is saved and the display returns to the TextBlock.
What doesn't work:
When a new topic is added the TextBox should have focus and the text selected so the user can enter a new name.
So my question is is there a point in the code or an event where I know that the TextBox has been created and is visible so I can set focus and select its contents. I've tried hooking into the SelectionChanged event but when that fires the TextBox hasn't yet been displayed. I also added an event to the OnAddTopicExecute method in the view model which I handled in the view, but again that fired before the TextBox was visible.
Below is the code that supports the above XAML. I've tried to cut it down, but there still seems to be a lot of it, so you can skip this if you're not interested ;)
Code behind:
private DateTime lastClickTime = DateTime.MinValue;
private Point lastClickPosition;
private void TopicTextBlock_MouseLeftButtonUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
{
UIElement element = sender as UIElement;
if ((DateTime.Now - this.lastClickTime).TotalMilliseconds > 300)
{
this.lastClickPosition = e.GetPosition(element);
this.lastClickTime = DateTime.Now;
}
else
{
Point position = e.GetPosition(element);
if (Math.Abs(this.lastClickPosition.X - position.X) < 4 && Math.Abs(this.lastClickPosition.Y - position.Y) < 4)
{
var textBlock = sender as TextBlock;
var editableHelpTopic = textBlock.DataContext as EditableHelpTopic;
editableHelpTopic.InEdit = true;
var parent = textBlock.Parent as Grid;
TextBox textBox = parent.Children.First(c => c.GetType() == typeof(TextBox)) as TextBox;
textBox.Focus();
textBox.SelectAll();
}
}
}
private void EditTopicTextBox_LostFocus(object sender, RoutedEventArgs e)
{
var textBox = sender as TextBox;
var editableHelpTopic = textBox.DataContext as EditableHelpTopic;
editableHelpTopic.InEdit = false;
if (!textBox.Text.Equals(editableHelpTopic.Description))
{
this.editViewModel.RenameTopic(textBox.Text);
}
}
View Model:
public EditViewModel()
{
...
this.AddTopicCommand = new DelegateCommand(this.OnAddTopicExecute, this.OnAddTopicCanExecute);
...
}
where DelegateCommand is an implemetation of ICommand.
private void OnAddTopicExecute(object parameter)
{
var newTopic = new EditableHelpTopic
{
Description = "NewTopic",
InEdit = true
};
this.HelpTopics.Add(newTopic);
this.SelectedPageId = newTopic.Description;
}
Definitions:
public class EditableHelpTopic : INotifyPropertyChanged
{
public bool InEdit { ... }
public string Description { ... }
}

It turned out to be simpler than I thought.
I just needed to add a Loaded event handler to the TextBox:
private void EditTopicTextBox_Loaded(object sender, RoutedEventArgs e)
{
var textBox = sender as TextBox;
var editableHelpTopic = textBox.DataContext as EditableHelpTopic;
if (editableHelpTopic.InEdit)
{
textBox.Focus();
textBox.SelectAll();
}
}