Develop Reference

Sorting an ObservableCollection after editing a property of an item

I'm trying to bind an ObservableCollection<T> to a DataGrid in WPF.
Below the DataGrid, there are fields to edit the currently selected item from the DataGridlike so:
So the generic T of the ObservableCollection<T> has the following properties:
- Title (Überschrift)
- Description (Beschreibung)
- Path (Pfad)
and it also has a property Reihenfolge which means Order.
With the yellow arrows, I want to be able to modify the order of the entries.
Unfortunately, the ObservableCollection doesn't have an OrderBy-method...
I've tried the following:
In XAML I have defined a CollectionViewSource like this:
<CollectionViewSource Source="{Binding Bilder}" x:Key="Pictures">
<CollectionViewSource.SortDescriptions>
<scm:SortDescription PropertyName="Reihenfolge" />
</CollectionViewSource.SortDescriptions>
</CollectionViewSource>
And I have binded the DataGrid to this CollectionViewSource
<DataGrid Grid.Column="0" Grid.Row="1"
Name="PictureDataGrid"
ItemsSource="{Binding Source={StaticResource Pictures}}"
AutoGenerateColumns="False"
IsReadOnly="True"
CanUserAddRows="false"
SelectedItem="{Binding SelectedBild}"
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch">
...
In the ViewModel, I have these properties:
public ObservableCollection<BildNotifiableModel> Bilder { get; set; }
public BildNotifiableModel SelectedBild { get; set; }
and two methods which are called with DelegateCommands that update the order
private void MoveSeiteUp()
{
const int smallestReihenfolge = 1;
if (this.SelectedBild.Reihenfolge > smallestReihenfolge) {
var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge - 1);
this.SelectedBild.Reihenfolge--;
bildToSwapReihenfolgeWith.Reihenfolge++;
RaisePropertyChanged(nameof(this.Bilder));
}
}
private void MoveSeiteDown()
{
if (this.SelectedBild.Reihenfolge < MaxAllowedImages) {
var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge + 1);
this.SelectedBild.Reihenfolge++;
bildToSwapReihenfolgeWith.Reihenfolge--;
RaisePropertyChanged(nameof(this.Bilder));
}
}
The order gets updated correctly, but unfortunately, the view doesn't reflect the changes... only after closing and reopening the view, the entries in the DataGrid are in the correct order.
What am I doing wrong here?
How can I make the DataGrid update, when changing the order?
Thanks in advance

I think the problem is that the CollectionView doesn't listen for the PropertyChanged-Events from its elements and also RaisePropertyChanged(nameof(this.Bilder)); dosen't work because the CollectionView is not really changed.
I would recomend to create the CollectionView in code via CollectionViewSource.GetDefaultView(list). So you can control the CollectionView from your model and call ICollectionView.Refresh if needed.

In your Methods, create a new Collection and add it to "Bilder". Just raising the PropertyChanged will execute an evaluation for referential equality. If it is the same - which it will be, if you just move items inside around - it will not update the DataGrid.
If you are not using the ObservableCollections attributes, like automatically updates, when items are added or removed, you might also change it to a "normal" List.
private void MoveSeiteUp()
{
const int smallestReihenfolge = 1;
if (this.SelectedBild.Reihenfolge > smallestReihenfolge) {
var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge - 1);
this.SelectedBild.Reihenfolge--;
bildToSwapReihenfolgeWith.Reihenfolge++;
this.Bilder = new ObservableCollection<BildNotifiableModel> (this.Bilder);
RaisePropertyChanged(nameof(this.Bilder));
}
}
private void MoveSeiteDown()
{
if (this.SelectedBild.Reihenfolge < MaxAllowedImages) {
var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge + 1);
this.SelectedBild.Reihenfolge++;
bildToSwapReihenfolgeWith.Reihenfolge--;
this.Bilder = new ObservableCollection<BildNotifiableModel> (this.Bilder);
RaisePropertyChanged(nameof(this.Bilder));
}
}

Two-way-binding: editing passed value from XAML control in the model setter does not update control

This is for a Windows 10 Universal App.
XAML:
<RelativePanel Padding="4" Margin="4,12,0,0">
<TextBlock x:Name="Label" Text="Class Name" Margin="12,0,0,4"/>
<ListView x:Name="ClassTextBoxes"
ItemsSource="{Binding TextBoxList}"
SelectionMode="None" RelativePanel.Below="Label">
<ListView.ItemTemplate>
<DataTemplate >
<RelativePanel>
<TextBox x:Name="tbox"
PlaceholderText="{Binding PlaceHolder}"
Text="{Binding BoxText,
Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}"
Padding="4" Width="200" MaxLength="25"/>
<TextBlock x:Name="errorLabel"
RelativePanel.Below="tbox"
Text="{Binding Error, Mode=TwoWay}"
Padding="0,0,0,4"
FontSize="10"
Foreground="Red"/>
<Button Content="Delete" Margin="12,0,0,0" RelativePanel.RightOf="tbox"/>
</RelativePanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</RelativePanel>
Model:
public class TextBoxStrings : BaseModel
{
private string _placeholder;
public string PlaceHolder
{
get { return _placeholder; }
set
{
if (_placeholder != value)
{
_placeholder = value;
NotifyPropertyChanged();
}
}
}
private string _boxText;
public string BoxText
{
get { return _boxText; }
set
{
if (_boxText != value)
{
_boxText = CheckBoxText(value);
NotifyPropertyChanged();
}
}
}
public string CheckBoxText(string val)
{
var r = new Regex("[^a-zA-Z0-9]+");
return r.Replace(val, "");
}
}
ViewModel:
private TrulyObservableCollection<TextBoxStrings> _textBoxList;
public TrulyObservableCollection<TextBoxStrings> TextBoxList
{
get { return _textBoxList; }
set
{
if (_textBoxList != value)
{
_textBoxList = value;
RaisePropertyChanged();
}
}
}
and I add new TextBoxString objects to my TextBoxList collection from within my view-model.
I want to make it that users can't type in certain characters (or rather, they get deleted whenever they
are typed in.
This works...in the model. Setting breakpoints and looking at the values, everything in the Model is working: value goes into the setter and gets changed, _boxText holds the new value that is set from CheckBoxText();
But the problem is, in my View, the textbox doesn't reflect changes to the underlying text that I make in the model.
So if I type in "abc*()" into "tbox", the value in the model will be "abc". The value of the textbox, however, will still be "abc*()".
I have a feeling it has something to do with the fact that I'm editing items that are inside of a collection and I don't have anything implemented to handle changing items within a collection. I was under the impression that using INotifyPropertyChanged and ObservableCollection<T> would take care of that for me.
Does anyone have any suggestions?
Thank you!
Edit: So, now I'm trying to use TrulyObservableCollection because I thought this was the problem, but it hasn't helped. Here it is: https://gist.github.com/itajaja/7507120

But the problem is, in my View, the textbox doesn't reflect changes to the underlying text that I make in the model.
As you've seen, the TextBox do reflect changes to your model. When you type in "abc*()" in the TextBox, the value in the model will be changed to "abc". The problem here is that the binding system in UWP is "intelligent". For TwoWay bindings, changes to the target will automatically propagate to the source and in this scenario, binding system assumes that the PropertyChanged event will fire for corresponding property in source and it ignores these events. So even you have RaisePropertyChanged or NotifyPropertyChanged in you source, the TextBox still won't update.
In WPF, we can call BindingExpression.UpdateTarget Method to force the update. But this method is not available in UWP.
As a workaround, you should be able to use TextBox.TextChanged event to check the input like following:
private void tbox_TextChanged(object sender, TextChangedEventArgs e)
{
var tb = sender as TextBox;
if (tb != null)
{
var originalText = tb.Text;
var r = new Regex("[^a-zA-Z0-9]+");
if (originalText != r.Replace(originalText, ""))
{
var index = (tb.SelectionStart - 1) < 0 ? 0 : (tb.SelectionStart - 1);
tb.Text = r.Replace(originalText, "");
tb.SelectionStart = index;
}
}
}
However it may break your MVVM model, you can use data validation to avoid this and here is a blog: Let’s Code! Handling validation in your Windows Store app (WinRT-XAML) you can refer to. And for my personal opinion, data validation is a better direction for this scenario.

if (_boxText != value)
{
_boxText = CheckBoxText(value);
NotifyPropertyChanged();
}
Try changing this to:
var tmp = CheckBoxText(value);
if (_boxText != tmp)
{
_boxText = tmp;
NotifyPropertyChanged();
}
I hope, in your XAML, the binding to property BoxText is two-way, right?

You should edit BoxText and then send checked value to UI. Just send value to CheckBoxText and already edited should be assigned to _boxText. And then you should send BoxText to UI by calling RaisePropertyChanged("BoxTest"). Please, see the following code snippet:
private string _boxText;
public string BoxText
{
get { return _boxText; }
set
{
if (_boxText != value)
{
_boxText=CheckBoxText(value);
RaisePropertyChanged("BoxText");
}
}
}
There is no difference where you use INotifyPropertyChanged for one property of for properties placed in collection. The complete example with collections and ListView can be seen here

Check a large group of checkboxes

I want to be able to say:
Get the first textblock, then the first checkbox, both with the number 1 in their name.
Then if the checkbox is checked, then the textblock can be populated.
See code:
for (int i = 1; i < 10; i++)
{
TextBlock a = (this.FindName(string.Format("tb_{0}", i)) as TextBlock);
CheckBox b = (this.FindName(string.Format("ck_{0}", i)) as CheckBox);
if (b.IsChecked.HasValue)
{
if (a != null) a.Text = data.ArrayOfSensors[i].ToString();
}
else
{
if (a != null) a.Text = data.ArrayOfSensors[0].ToString();
}
}
So when the checkbox is enabled, the textblock will be populated with the index from the array.
Many thanks!
EDIT: A slightly better explanation:
The textblocks are named: tb_1, tb_2 etc
The Checkboxes are named: cb_1, cb_2 etc
The array is:
[0] 0
[1] 100
[2] 150
The number is what they all have in common. So I can use a for loop with i as a common variable for each. I also have about 50 textboxes and Comboboxes and don't want to write each one out individually.
EDIT: My ComboBoxes and Textblocks are created on Xaml code like this:
<CheckBox x:Name="Cb_1" Width="15" Height="15" Margin="349,53,127,164" IsChecked="True" />
<TextBlock x:Name="tb_1" Text="80" Height="20" Width="20" Margin="266,35,205,177" />

Its hard to answer without seeing what your XAML looks like, however it sounds like you may be trying to use WPF like it is WinFirms.
To build an interface like this in WPF, you should start by creating a custom class to hold your data, and then use an ItemsControl to render your collection of data.
For example, your class might look something like this
public class SensorData() : INotifyPropertyChanged
{
// should implement INotifyPropertyChanged of course
public string Text { get; set; }
public bool IsChecked { get; set; }
}
And an ObservableCollection<SensorData> might be rendered using an <ItemsControl> with a ItemsPanelTemplate containing both a CheckBox and a TextBox
<ItemsControl ItemsSource="{Binding MyCollectionOfSensorData}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<CheckBox Checked="{Binding IsChecked}" />
<TextBlock Text="{Binding Text}" />
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
This will loop through the collection of SensorData objects, and render a CheckBox and TextBox for each one. If you want to do any manipulation of the data from the code-behind, you only need to modify the properties of the SensorData objects.
For example, you could have a loop that goes
for (int i = 0; i < MyCollectionOfSensorData.Length; i++)
{
SensorData item = MyCollectionOfSensorData[i];
if (item.IsChecked)
item.Text = data.ArrayOfSensors[i].ToString();
else
item.Text = "0";
}
And there would be no interaction with the UI objects at all.

How to dynamically link a CheckBox to enable a TextBox in C# (WPF)?

I have a row in a grid with 5 textboxes, 2 of which are enabled by checkboxes. I am trying to dynamically add additional rows to the grid when a button is clicked. The eventhandler I added will only enable the textbox in the first row, but not in the current row (2nd). There is another eventhandler which handles the box in the first row, this is a new one. (BTW I only have part of the second row coded). Not sure if I should try making a template for the checkbox, and then use binding to the textbox? And if so, the instructions I've read on connecting the binding are vague and confusing. Or can I do the binding directly? Or ?
public partial class Window2 : Window
{
int currentColumn = 0;
int currentRow = 1;
int timesCalled = 1;
public Window2()
{
InitializeComponent();
}
private void AddLevelButton_Click(object sender, RoutedEventArgs e)
{
string level = this.Level.Content.ToString(); //label for the row
string[] splitLevel = level.Split(' ');
int levelNum = int.Parse(splitLevel[1]);
levelNum = timesCalled + 1;
int nextRow = currentRow + 1;
int nextColumn = currentColumn + 1;
Label levelLabel = new Label();
levelLabel.Content = "Level " + levelNum.ToString();
Grid.SetRow(levelLabel, nextRow);
Grid.SetColumn(levelLabel, currentColumn);
FlowGrid.Children.Add(levelLabel);
currentColumn++;
CheckBox antesBox = new CheckBox(); //the checkbox to enable the
antesBox.Name = "AntesBox"; //textbox which follows
antesBox.VerticalAlignment = VerticalAlignment.Bottom;
antesBox.HorizontalAlignment = HorizontalAlignment.Right;
antesBox.FontSize = 16;
antesBox.Width = 20;
antesBox.Height = 20;
antesBox.Checked += AntesBox_Checked1; //eventhandler
Grid.SetRow(antesBox, nextRow);
Grid.SetColumn(antesBox, currentColumn);
FlowGrid.Children.Add(antesBox);
nextColumn = ++currentColumn;
TextBox enterAntes = new TextBox(); //the textbox to be enabled
enterAntes.Name = "EnterAntes";
enterAntes.Margin = new Thickness(5, 0, 5, 0);
enterAntes.FontSize = 16;
enterAntes.FontFamily = new FontFamily("Verdana");
enterAntes.IsEnabled = false;
enterAntes.KeyDown += EnterAntes_KeyDown1; //tested; this works
Grid.SetRow(EnterAntes, nextRow);
Grid.SetColumn(EnterAntes, nextColumn);
FlowGrid.Children.Add(EnterAntes);
nextColumn = ++currentColumn;
}
private void enterAntes_KeyDown1(object sender, KeyEventArgs e)
{
int key = (int)e.Key;
e.Handled = !(key >= 34 && key <= 43 ||
key >= 74 && key <= 83 || key == 2);
}
private void AntesBox_Checked1(object sender, RoutedEventArgs e)
{
EnterAntes.IsEnabled = true;
}

You need to add following codes to enable text boxes.
Following is the xaml view of the datagrid.
<DataGrid x:Name="gvTest" AutoGenerateColumns="False" ItemsSource="{Binding}" HorizontalAlignment="Left" Margin="86,204,0,0" VerticalAlignment="Top" Height="132" Width="436">
<DataGrid.Columns>
<DataGridTemplateColumn Header="TextBox 01">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBox x:Name="txt01" Width="50" Text="{Binding TxtBox01}"></TextBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
<DataGridTemplateColumn Header="TextBox 02">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBox x:Name="txtbox02" Width="50" Text="{Binding TxtBox02}"></TextBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
<DataGridTemplateColumn Header="TextBox 03">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBox x:Name="txtbox03" Width="50" Text="{Binding TxtBox03}"></TextBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
<DataGridTemplateColumn Header="TextBox 04">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBox x:Name="txtbox04" Width="50" IsEnabled="False" Text="{Binding TxtBox04}" Loaded="txtbox04_Loaded"></TextBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
<DataGridTemplateColumn Header="TextBox 05">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBox x:Name="txtbox05" Text="{Binding TxtBox05}" Loaded="txtbox05_Loaded"></TextBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
<DataGridTemplateColumn Header="Enable" >
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<CheckBox x:Name="chk01" Checked="chk01_Checked" IsChecked="{Binding IsActive}"></CheckBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
</DataGrid.Columns>
</DataGrid>
add the following codes to declare instance of required textboxes and declare observable collection.
TextBox txt04;
TextBox txt05;
ObservableCollection<TestItem> TestItemList = new ObservableCollection<TestItem>();
add the following codes to the loaded event of the required textboxes.
private void txtbox04_Loaded(object sender, RoutedEventArgs e)
{
txt04 = (sender as TextBox);
//txt04.IsEnabled = false;
}
private void txtbox05_Loaded(object sender, RoutedEventArgs e)
{
txt05 = (sender as TextBox);
}
Now, create a model class with following code segment in order to bind values to the datagrid.
public class TestItem
{
public string TxtBox01 { get; set; }
public string TxtBox02 { get; set; }
public string TxtBox03 { get; set; }
public string TxtBox04 { get; set; }
public string TxtBox05 { get; set; }
public bool IsActive { get; set; }
public TestItem()
{
IsActive = false;
}
}
I have used a button to add new rows to the datagrid. add the following codes to the button click to add rows.
private void btnAdd_Click(object sender, RoutedEventArgs e)
{
TestItemList.Add(new TestItem());
gvTest.ItemsSource = TestItemList;
}
Finally, add the following codes to the checkbox checked event
CheckBox c = (sender as CheckBox);
if (c.IsChecked==true)
{
txt04.IsEnabled = true;
txt05.IsEnabled = true;
}
Hope this helps you to fulfill your requirement.

At the risk of perpetuating the wrong approach, it seems to me that the most direct way to address your specific need here is to fix your event handler so that it is always specific to the text box that corresponds to the checkbox in question. This is most easily done by moving the event handler subscription to below the declaration of the local variable enterAntes, and then use that variable in the event handler (i.e. so that it's capture by the anonymous method used as the event handler). For example:
TextBox enterAntes = new TextBox(); //the textbox to be enabled
antesBox.Checked += (sender, e) => enterAntes.IsEnabled = true;
Now, that said, I whole-heartedly agree with commenter Mark Feldman who suggests that the code you've written is not the right way to accomplish your goal in WPF.
I'm not sure I agree with the characterization "harder". That's such a loaded and subjective term, depending in no small part in what you find easy or hard. Being new to WPF, you almost certainly find the concepts of data binding and declarative XAML-based coding "hard", and direct, procedural code such as in your example "easy" (or at least "easier" :) ).
But he's absolutely right that in the long run, you will be better served by doing things "the WPF way". You may or may not wind up with much less code, but the WPF API is designed to be leveraged as much as possible from the XAML, and use code-behind minimally (and certainly not for the purpose to build the UI).
So what's all that mean for your code? Well, I ramble and it would be beyond the scope of a good, concise Stack Overflow answer for me to try to rewrite your entire code from scratch to suit the WPF paradigm. But I will offer some suggestions as to how I'd handle this.
First, forget the UI objects themselves for a moment. Write classes that describe the key characteristics of the UI as you want it to be, without being the UI itself. In this example, this could mean that you should have a list of rows. There should also be a class that defines what a single row looks like, e.g. with a bool property (to reflect the checkbox state) and a string property (to reflect the text box value). This is your "model"; i.e. each class is an individual model class, and at the same time you could consider the entire collection of classes as the model for your UI.
Now, go back to your UI and define it in XAML, not in code. There are several different ways to represent a list in the UI. Classes like ListBox, ListView, DataGrid, or even ItemsControl (the base class for many of the list-oriented controls). Bind the source of your list control to the model list you created in the previous step.
Define a DataTemplate (again, in XAML) for the type of class that is contained in the list. This will declare the UI for a single row in your list. Your template might look something like this:
<!-- Make sure you defined the "local" XML namespace for your project using the
xmlns declaration -->
<DataTemplate DataType="{x:Type local:MyRowModel}">
<StackPanel Orientation="Horizontal">
<TextBox Text="{Binding Text}" IsEnabled={Binding IsEnabled}"/>
<Checkbox Checked="{Binding IsEnabled}"/>
</StackPanel>
</DataTemplate>
All of the XAML inside the DataTemplate element tells WPF what you want a single row to look like, within the control that is presenting your row model. That control will set the DataContext for the list item defined by the template, such that the {Binding...} declarations can reference your row model's properties directly by name.
That row model in turn might look something like this:
class MyRowModel : INotifyPropertyChanged
{
private string _text;
private bool _isEnabled;
public string Text
{
get { return _text; }
set
{
if (_text != value)
{
_text = value;
OnPropertyChanged();
}
}
}
public bool IsEnabled
{
get { return _isEnabled; }
set
{
if (_isEnabled != value)
{
_isEnabled = value;
OnPropertyChanged();
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([CallerMemberName]string propertyName = null)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
When your button to add a new item is clicked, don't mess with the UI directly. Instead, add a new element to your list of rows. Let WPF do the work of updating the UI to match.
NOTES:
The above uses StackPanel for the data template for convenience. If you want things lined up in columns, you'll probably want to use a Grid and declare its columns using SharedSizeGroup.
Or better yet, maybe you can use DataGrid which, assuming its default presentation of the values is acceptable to you, offers simple and automatic handling of exactly this type of layout.
The above is not meant to be anything close to a complete explanation of how to use data templating. It's just supposed to get you pointed in the right direction. Templating is one of WPF's more powerful features, but with that it also has the potential to be fairly complex.
For all of this to work, your types need to provide notification when they change. In the case of the row model, you can see it implements INotifyPropertyChanged. There is also an interface INotifyCollectionChanged; usually you don't have to implement this yourself, as WPF has the type ObservableCollection<T> which you can use just like List<T>, to store lists of data but with a way for notifications of changes to be reported to WPF.
I know this is a lot to take it all at once. Unfortunately, it's not feasible to try to explain all in a single answer all the things you need to learn to get this right. Frankly, even the above is pushing the limits as to what's within the scope of a Stack Overflow answer. But I hope that I've hit just the right highlights to get you looking at the right parts of the WPF documentation, and to understand the underlying philosophy of the WPF API.

change textblock text that is inside Listbox in windowsphone 8

i want to change textblock text in page initialize event
here is my xaml
<ListBox Margin="3,60,1,10" BorderThickness="2" Grid.Row="1" Name="lstAnnouncement" Tap="lstAnnouncement_Tap" Width="476" d:LayoutOverrides="VerticalMargin">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Name="thispanel" Grid.Row="1" Orientation="Horizontal" Height="120" Width="478" >
<StackPanel.Background>
<ImageBrush ImageSource="Images/Text-ALU.png" Stretch="Fill" />
</StackPanel.Background>
<Grid HorizontalAlignment="Left" Width="30" Margin="0,0,0,2" Background="#FF0195D5" Height="118">
<TextBlock x:Name="txtDate" TextWrapping="Wrap">
</TextBlock>
</Grid>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
i want to change txtDate.Text using c# in code-behind but txtdate is not accessible in code behind so how to achieve it ?

The reason you're not able to access the txtDate object is because it's contained within the DataTemplate you're using for the ListBox. This isn't an error - the DataTemplate is being applied to every single item added to your ListBox.
Given that the ListBox creates, among other controls, a Grid containing a TextBlock with the name "txtDate", for every single item added to it, what would it mean to access the txtDate object? How would your program decide which of a (functionally) infinite number of txtDates associated with an identical number of ListBoxItems you meant when you referenced txtDate?
If you wanted to be able to easily change the content of txtDate, you'd want to bind the ItemsSource of your ListBox to a property in a ViewModel. The easiest way to do this would be to have that property be an IEnumerable containing a custom model type. This way, you could update the text property of that model and call NotifyPropertyChanged on the that property, and the UI would update to reflect the new data.
Here's an example:
public class YourViewModel
{
public List<YourModel> Models { get; set; }
}
public class YourModel : INotifyPropertyChanged
{
private string yourText;
public string YourText
{
get { return yourText; }
set
{
yourText = value;
NotifyPropertyChanged("YourText");
}
}
// add INotifyPropertyChanged implementation here
}
And then you'd want to bind the ItemsSource of the ListBox to YourViewModel's Models property, and the text of your TextBox to the YourModel's YourText property. Any time you change the YourModel.YourText property, it'll automatically update on the UI. I think it's probably subject to debate whether having your model implement INotifyPropertyChanged is proper MVVM, but I find it a lot easier in these cases than forcing the ViewModel to update every single model each time a change is made on one of them.
If you're not familiar with the MVVM pattern used with WPF, this might be a good start: MVVM example.

this function will help you... This will help u find the control inside of a listbox runtime..
public FrameworkElement SearchVisualTree(DependencyObject targetElement, string elementName)
{
FrameworkElement res = null;
var count = VisualTreeHelper.GetChildrenCount(targetElement);
if (count == 0)
return res;
for (int i = 0; i < count; i++)
{
var child = VisualTreeHelper.GetChild(targetElement, i);
if ((child as FrameworkElement).Name == elementName)
{
res = child as FrameworkElement;
return res;
}
else
{
res = SearchVisualTree(child, elementName);
if (res != null)
return res;
}
}
return res;
}
Here first parameter is parent and the second parameter is the name of the element which in your case is "txtDate".. hope it works!!