I've run out of ideas trying to collapse a DataGridTextcolumn depending on a value set in a public property (in a WPF/XAML/MVVM Light application).
An extract of the xaml is:
<StackPanel>
<DataGrid AutoGenerateColumns="False" Name="PipelinesGrid"
HorizontalAlignment="Left"
ItemsSource="{Binding Pipelines}"
SelectedItem="{Binding SelectedPipelineView, Mode=TwoWay}"
VerticalAlignment="Top" Margin="10,16,0,0"
SelectionUnit="FullRow" SelectionMode="Single"
CanUserAddRows="False">
<DataGrid.Columns>
<DataGridTextColumn
Binding="{Binding DailyCapacity, Mode=TwoWay}"
Header="Capacity(d)"
Visibility="{Binding Source={x:Reference PipelinesGrid},
Path=DataContext.ShowCapacities}"/>
Here is the Visibility setting is one of many that I've tried (this one gives a cycylical dependency error).
A relevant extract of the ViewModel code is:
private string _showCapacities;
public string ShowCapacities
{
get { return _showCapacities; }
set { _showCapacities = value; RaisePropertyChanged("ShowCapacities"); }
}
private void OnProjectSelected(ProjectSelectedArgs obj)
{
_selectedProject = obj.SelectedProject;
if (_selectedProject != null)
{
Pipelines = new ObservableCollection<PipelineView>();
foreach (var projectPipeline in _selectedProject.ProjectPipelines)
{
Pipelines.Add(new PipelineView(projectPipeline));
}
switch (_selectedProject.ProjectCategory.ProjectCategory1)
{
case "Upstream":
ShowCapacities = "Collapsed";
break;
case "Mid-Stream":
ShowCapacities = "Visible";
break;
}
}
IsEditing = false;
}
I've been informed by this article (http://stackoverflow.com/questions/8847661/datagridtextcolumn-visibility-binding) that I needed to use Source and Xreference. Thanks for any help.
There are various articles on SO that discuss this problem. Search for "wpf visibility binding datagrid column".
The problem is because DataGrid columns don't belong to the visual or logical tree of the DataGrid, so WPF can't find a suitable DataContext. Trying to use a relative or element binding fails as well.
Needless to say, some clever people have already solved this issue. My favourite solution is the proxy freezable method explained here: http://www.thomaslevesque.com/2011/03/21/wpf-how-to-bind-to-data-when-the-datacontext-is-not-inherited/ which worked fine for me.
Related
Suppose I am making a simple UWP application which navigates through several pages. I would like to have a common background for all pages, depending on which background a user has selected from the Settings page.
I have a SettingsPage.xaml with a comboBox (and Grid Background that needs to change):
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<ComboBox Name="ColourSelect" SelectionChanged="ComboBox_SelectionChanged">
<ComboBoxItem Name="Red">Red</ComboBoxItem>
<ComboBoxItem Name="Green">Green</ComboBoxItem>
<ComboBoxItem Name="Blue">Blue</ComboBoxItem>
</ComboBox>
</Grid>
Which interfaces with my SettingsPage.xaml.cs file:
private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
// Change background
if (Red.IsSelected) { } // Change to Red.png
else if (Green.IsSelected) { } // Change to Green.png
else if (Blue.IsSelected) { } // Change to Blue.png
}
I have set up my App.xaml to contain a background resource, but I'm not sure how to bind it to the C# in Settings.xaml.cs.
<Application.Resources>
<Style TargetType="Grid" x:Key="CommonBackground">
<Setter Property="Background" Value="{ <!-- Some image. How to bind? --> }"
</Style>
</Application.Resources>
What should I return to bind the user decision to the Application resources?
Thank you in advance!
This requires few changes in different pieces of application. Follow my steps.
In this case I a am creating two Resources. One that will maintain the Settings Combobox Colour Scheme. Second one is BitMapImage in Resource.
So my Application.Resource will look something like below.
<Application.Resources>
<image:BitmapImage x:Key="BackgroundSource" UriSource="ms-appx:///Assets/Red.png" />
<x:String x:Key="BackgroundBrush">Red</x:String>
</Application.Resources>
Make sure you are adding xmlns:image="using:Windows.UI.Xaml.Media.Imaging" in your App.xaml.
Now Create a Static Method inside App.xaml.cs that will be used to update Background to the Page during Run time. It should be something like below.
public static void UpdateBGColors(string Color)
{
switch (Color)
{
case "Red":
Current.Resources["BackgroundSource"] = "ms-appx:///Assets/Red.png";
break;
case "Green":
Current.Resources["BackgroundSource"] = "ms-appx:///Assets/Green.png";
break;
case "Blue":
Current.Resources["BackgroundSource"] = "ms-appx:///Assets/Blue.png";
break;
default:
Current.Resources["BackgroundSource"] = "ms-appx:///Assets/Red.png";
break;
}
}
Now Your combobox_SelectionChanged should look like below.
private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
ComboBox cb = sender as ComboBox;
ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings;
localSettings.Values["BackgroundBrush"] = (cb.SelectedValue as ComboBoxItem).Content;
App.UpdateBGColors((cb.SelectedValue as ComboBoxItem).Content.ToString());
}
Now you need to wire up the Background of each page to the Resource BackgroundSource. So anywhere you want the background to be set based on settings add below lines of code
<Grid>
<Grid.Background>
<ImageBrush ImageSource="{StaticResource BackgroundSource}" />
</Grid.Background>
......
</Grid>
At this point, if you change the setting in setting page and if you navigate back to original page that you came into setting page, The background should be set automatically to whatever you selected in Settings.
But you also want to make sure the same background is loaded when the app is opened next time. To do that in App.xaml.cs, Add below lines in the beginning of OnLaunched Event.
ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings;
if (localSettings.Values["BackgroundBrush"] != null)
{
UpdateBGColors(localSettings.Values["BackgroundBrush"].ToString());
}
Since in settings page, you are saving BackgroundBrush Everytime you change the Combobox Item, Whenever your app is loading, Based on the BackgroundBrush BackgroundSource will be assigned to correct Uri and will be used as Page Backhground.
Full Repo is available Here
Good Luck.
[Update] You can use this, and after save your settings.
SettingsPage.xaml
<Grid>
<Grid.Background>
<ImageBrush x:Name="colorImage" Stretch="UniformToFill"/>
</Grid.Background>
<ComboBox Name="ColourSelect" SelectionChanged="ComboBox_SelectionChanged">
<ComboBoxItem Name="Red">Red</ComboBoxItem>
<ComboBoxItem Name="Green">Green</ComboBoxItem>
<ComboBoxItem Name="Blue">Blue</ComboBoxItem>
</ComboBox>
</Grid>
SettingsPage.xaml.cs
private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (Red.IsSelected)
{
ChangeColorImage("ms-appx:///Assets/Red.png");
}
else if (Green.IsSelected)
{
ChangeColorImage("ms-appx:///Assets/Green.png");
}
else if (Blue.IsSelected)
{
ChangeColorImage("ms-appx:///Assets/Blue.png");
}
}
private void ChangeColorImage(string imageUrl)
{
// using Windows.UI.Xaml.Media.Imaging;
BitmapImage imageSource = new BitmapImage(new Uri(imageUrl));
colorImage.ImageSource = imageSource;
}
Using Caliburn.Micro for a WinRT application, I would like to control the ZIndex of items displays in an ItemsControl.
When a user taps on an item, it should become the topmost element.
<ItemsControl Background="White" Height="auto" Width="auto" x:Name="Parts"
HorizontalAlignment="Left"
VerticalAlignment="Top"
>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas></Canvas>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
The viewmodel bound to the view above contains a property Parts:
private BindableCollection<IPartViewModel> _parts = new BindableCollection<IPartViewModel>();
public BindableCollection<IPartViewModel> Parts
{
get { return _parts; }
set { _parts = value; NotifyOfPropertyChange(() => Parts); }
}
IPartViewModel has different implementations, each with their own View (= custom user controls).
Every implementation of IPartViewModel has a ZIndex property, ready to be bound.
All other bindings (labels, the tapped event, ...) work perfectly, but I cannot figure out what the binding should look like to control the ZIndex.
Many other questions on SO deal with this issue, but none for WinRT.
I ended up achieving this with a custom ItemsControl and overriding the method GetContainerForItemOverride where I return a ContentPresenter with a binding added to the ZIndex property
protected override DependencyObject GetContainerForItemOverride()
{
var cp = new ContentPresenter();
cp.SetBinding(Canvas.ZIndexProperty, new Binding { Path = new PropertyPath("ZIndex") });
return cp;
}
I would like to create something like CameraCaptureUI.CaptureFileAsync which will return the result to caller (location that user picked through bing maps in my case)
(the same question was asked here but I still need full screen UI or more complete code example)
Assuming the next use case:
CallerPage1 Navigate-> CallerPage2 (through Frame.Navigate(typeof(CallerPage2)) )
CallerPage2 Navigate-> LocationPickingPage (again through Frame.Navigate(typeof(LocationPickingPage )) <- here should be something else but not Frame.Navigate)
User picks a Location and presses done -> location object returned to CallerPage2
(through Frame.Navigate(typeof(CallerPage2)) )
And now if user presses back on CallerPage2 he/she will be navigated back to LocationPickingPage which is expected in navigation model described above but I wont to navigate him/her to CallerPage1
So this is how CameraCaptureUI.CaptureFileAsync behaves.
Maybe someone can help to look "behind the scenes" of CaptureFileAsync or familiar method and provide some example of how it can be implemented so that location picking can be performed like this:
Location location = await new LocationPickCaptureUI.CaptureLocationAsync();
Any help would be appreciated!
Edit
So, maybe someone can shad some light on how pages can share their data without affecting navigation history. I'm just looking for something like android's startActivityForResult.
I spend several days on this problem (msdn docs, researching different examples, forums and different sites including this one) and didn't find any approach so I think it is time to ask own question.
Sharing data between pages in manner I am looking for should be something obvious. Maybe I was looking in a wrong way but the problem is still persist's.
And please, if someone votes down my question share your mind and your source of knowledge as I still need help on this problem.
Thanks in advance
So, finally I've got an appropriate solution and maybe it can be helpful to anybody else.
The idea is to use Popup object and fit all the screen (however the details seemed like some kind of magic :) )
One thing: I used UserControl (in Visual Studio right click on project -> Add -> new item.. -> UserControl) template as in this scenario it is easy to manage popups's content
Here is the full source for C#:
CustomCaptureUI.xaml:
<UserControl
x:Class="Family.CustomCaptureUI"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Family"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="300"
d:DesignWidth="400"
x:Name="Root">
<Grid>
<Border BorderBrush="Gray" BorderThickness="1">
<Grid x:Name="Panel" Background="Gray">
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<StackPanel Grid.Column="1" VerticalAlignment="Center">
<TextBlock Text="New text" Foreground="LightGray" FontSize="18"/>
<TextBox x:Name="ToDoText" Width="Auto" BorderBrush="Black" BorderThickness="1" VerticalAlignment="Center"/>
<StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
<Button x:Name="SubmitButton" Background="Gray" Content="Submit" HorizontalAlignment="Center"/>
<Button x:Name="CancelButton" Background="Gray" Content="Cancel" HorizontalAlignment="Center"/>
</StackPanel>
</StackPanel>
</Grid>
</Border>
</Grid>
</UserControl>
CustomCaptureUI.xaml.cs:
public sealed partial class CustomCaptureUI : UserControl
{
public enum ResultStatuses
{
Canceled,
Ok,
None
}
public CustomCaptureUI()
{
_resultStatus = ResultStatuses.None;
// force content's size to preferable value
Root.Width = Window.Current.Bounds.Width;
Root.Height = Window.Current.Bounds.Width * 0.3;
// Init popup's Content
_popup.Child = this;
// Init popups's position
_popup.SetValue(Canvas.LeftProperty, (Window.Current.Bounds.Width - Root.Width) * 0.5);
_popup.SetValue(Canvas.TopProperty, (Window.Current.Bounds.Height - Root.Height) * 0.5);
}
public async Task<string> ShowDialog()
{
string result = string.Empty;
if (_semaphore != null) { DismissAddToDoPopup(); }
// Init a Task for block the ShowDialog-method until user presses Cancel or Submit
_semaphore = new Task(() => { });
CancelButton.Click += (sender, e) =>
{
_resultStatus = ResultStatuses.Canceled;
DismissAddToDoPopup();
};
SubmitButton.Click += (sender, e) =>
{
result = ToDoText.Text;
_resultStatus = ResultStatuses.Ok;
DismissAddToDoPopup();
};
ShowAddToDoPopup();
// actual blocking of ShowDialog
await _semaphore;
return result;
}
public void DismissDialog()
{
_resultStatus = ResultStatuses.Canceled;
DismissAddToDoPopup();
}
private void ShowAddToDoPopup()
{
ToDoText.Text = string.Empty;
_popup.IsOpen = true;
}
private void DismissAddToDoPopup()
{
if (_semaphore != null)
{
// starts the task and allows awaited ShowDialog-method to be released
// after _semaphore is finishing
_semaphore.Start();
_semaphore = null;
}
_popup.IsOpen = false;
}
public ResultStatuses ResultStatus
{
get { return _resultStatus; }
}
private Popup _popup = new Popup();
private Task _semaphore;
private ResultStatuses _resultStatus;
}
And then it can be used like this:
var dialog = new CustomCaptureUI();
string result = await dialog.ShowDialog();
if (dialog.ResultStatus == AddToDoDialog.ResultStatuses.Ok)
{
// Useful stuff
if (!string.IsNullOrWhiteSpace(result))
{
...
}
}
Hope it can save someone's time a little
I have been messing with something that works in the code behind but when I try and bind to a MVVM , nothing displays. First I will show the code behind, then MVVM ( same xaml ). I want to use MVVM and not code behind.
Code Behind (works):
var loadOp = ctx.Load<GateBlox.Web.Models.Structure>(ctx.GetStructuresQuery());
loadOp.Completed += (s, e) => { _treeView.ItemsSource = loadOp.Entities.Where(struc => !struc.StructureParentFK.HasValue); };
XAML
<Grid x:Name="LayoutRoot">
<sdk:TreeView x:Name='_treeView' DataContext='{StaticResource ViewModel}'>
<sdk:TreeView.ItemTemplate>
<sdk:HierarchicalDataTemplate ItemsSource='{Binding Children}'>
<TextBlock Text='{Binding StructureName}' />
</sdk:HierarchicalDataTemplate>
</sdk:TreeView.ItemTemplate>
</sdk:TreeView>
</Grid>
MVVM (doesnt bind)
private LoadOperation<Structure> _loadStructures;
private StructureContext _structureContext;
private IEnumerable<Structure> _structures;
public IEnumerable<Structure> Structures
{
get { return this._structures; }
set { this._structures = value; RaisePropertyChanged("Structures"); }
}
public StructuresViewModel()
{
if (!DesignerProperties.IsInDesignTool)
{
_structureContext = new StructureContext();
_loadStructures = _structureContext.Load(_structureContext.GetStructuresQuery().Where (p=> ! p.StructureParentFK.HasValue));
_loadStructures.Completed += new EventHandler(_loadStructures_Completed);
}
}
void _loadStructures_Completed(object sender, EventArgs e)
{
this.Structures = _loadStructures.Entities;
}
Have your checked that you are not getting a binding expression error in the output? You are binding the items source of the data template to a property named Children, but your view model exposes a data source named Structures.
Also, in your working example, you are setting the ItemsSource of the TreeView, but in your MVVM XAML you are setting the ItemsSource of your data template. Is there an inconsistency between what ItemsSource you need to set/bind to?
You might also consider using a collection data source that implements the INotifyCollectionChanged interface (ObservableCollection or expose the binding source as a ICollectionView that uses a PagedCollectionView).
I recommend you take a look at this information about data binding in MVVM, as it provides excellent guidance on setting up data sources in your view models.
You are not setting the ItemsSource for your TreeView. I think your xaml should look something like this:
<Grid x:Name="LayoutRoot">
<sdk:TreeView x:Name='_treeView' DataContext='{StaticResource ViewModel}'
ItemsSource="{Binding Structures}">
<sdk:TreeView.ItemTemplate>
<sdk:HierarchicalDataTemplate ItemsSource='{Binding Children}'>
<TextBlock Text='{Binding StructureName}' />
</sdk:HierarchicalDataTemplate>
</sdk:TreeView.ItemTemplate>
</sdk:TreeView>
</Grid>
Hope this helps :)
I almost have it working now. I took a different approach and went with a HeirarchicalDataTemplate. At the moment the data is showing but not correctly: The child1 record is shwoing up as a parent as well.
Parent1(level1)
Parent2(level1)
Child1(level2)
Child1(level1)
<navigation:Page x:Class="GateBlox.Views.Structure"
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"
mc:Ignorable="d"
xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"
d:DesignWidth="640"
d:DesignHeight="480"
Title="Structure Page"
xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk"
xmlns:viewmodel="clr-namespace:GateBlox.ViewModels">
<UserControl.Resources>
<viewmodel:StructuresViewModel x:Key='ViewModel'>
</viewmodel:StructuresViewModel>
</UserControl.Resources>
<Grid x:Name="LayoutRoot"
DataContext='{StaticResource ViewModel}'>
<Grid.Resources>
<sdk:HierarchicalDataTemplate x:Key="ChildTemplate"
ItemsSource="{Binding Path=Parent}">
<TextBlock FontStyle="Italic"
Text="{Binding Path=StructureName}" />
</sdk:HierarchicalDataTemplate>
<sdk:HierarchicalDataTemplate x:Key="NameTemplate"
ItemsSource="{Binding Path=Children}"
ItemTemplate="{StaticResource ChildTemplate}">
<TextBlock Text="{Binding Path=StructureName}"
FontWeight="Bold" />
</sdk:HierarchicalDataTemplate>
</Grid.Resources>
<sdk:TreeView x:Name='treeView'
Width='400'
Height='300'
ItemsSource='{Binding Structures}'
ItemTemplate='{StaticResource NameTemplate}'>
</sdk:TreeView>
</Grid>
using System;
using System.Collections.ObjectModel;
using GateBlox.Web.Models;
using System.ServiceModel.DomainServices.Client;
using GateBlox.Web.Services;
using GateBlox.Helpers;
using System.ComponentModel;
using System.Collections.Generic;
namespace GateBlox.ViewModels
{
public class StructuresViewModel : ViewModelBase
{
private LoadOperation<Structure> _loadStructures;
private StructureContext _structureContext;
private ObservableCollection<Structure> _structures;
public ObservableCollection<Structure> Structures
{
get { return this._structures; }
set { this._structures = value; RaisePropertyChanged("Structures"); }
}
public StructuresViewModel()
{
if (!DesignerProperties.IsInDesignTool)
{
_structureContext = new StructureContext();
_loadStructures = _structureContext.Load(_structureContext.GetStructuresQuery());
_loadStructures.Completed += new EventHandler(_loadStructures_Completed);
}
}
void _loadStructures_Completed(object sender, EventArgs e)
{
this.Structures = IEnumerableConverter.ToObservableCollection(_loadStructures.Entities);
}
}
}
I'm trying to do a two way binding of the SelectedIndex attribute of a ListPicker in a Windows Phone 7 UserControl.
It raises the following exception when I set the DataContext:
SelectedIndex must always be set to a valid value.
This is the XAML code
<Grid x:Name="LayoutRoot">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<toolkit:ListPicker
Grid.Row="0"
x:Name="List1"
SelectionChanged="Picker_SelectionChanged"
SelectedIndex="{Binding PickerSelectedIndex, Mode=TwoWay}"
ItemTemplate="{StaticResource PickerTemplate}"
ItemsSource="{Binding MyList}"/>
</Grid>
And the code behind in DataContext
private ObservableCollection<MyClass> myList = null;
public ObservableCollection<MyClass> MyList
{
get { return this.myList; }
set
{
if (value != this.myList)
{
this.myList= value;
NotifyPropertyChanged("MyList");
this.PickerSelectedIndex = 0;
}
}
}
private int pickerSelectedIndex = 0;
public int PickerSelectedIndex
{
get
{
return this.pickerSelectedIndex;
}
set
{
this.pickerSelectedIndex= value;
}
}
Putting a breakpoint in PickerSelectedIndex.get I can see that it is returned correctly (0).
I am sure that the problem is SelectedIndex="{Binding PickerSelectedIndex, Mode=TwoWay}" because deleting this line solves the problem, and I can see the ListPicker correctly loaded with the data from MyList.
I can't see where is the problem...
Moving SelectedIndex after ItemsSource solved the problem.
This is the working snippet
<toolkit:ListPicker
Grid.Row="0"
x:Name="List1"
SelectionChanged="Picker_SelectionChanged"
ItemTemplate="{StaticResource PickerTemplate}"
ItemsSource="{Binding MyList}"
SelectedIndex="{Binding PickerSelectedIndex, Mode=TwoWay}"/>
Anyone have an explanation for this?
My guess would be that the binding is being applied with a default value of zero when created and before the items exist. It's therefore trying to select the first item (with a zero index) before that item is created.
Try making sure that the ViewModel property of PickerSelectedIndex defaults to -1.
You may also want to delay setting the binding until the items are created.
Matt Lacey is right; binding happens before the data items get populated & hence the error. If you have an event handler for SelectionChanged, you will notice that a breakpoint in it will be hit as the page/listpicker loads. Here is one way to get around this initialization issue:
private void SomeListPicker_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
// Make sure we don't handle the event during initiation.
if (e.RemovedItems != null && e.RemovedItems.Count > 0)
{
if (this.SomeListPicker.SelectedItem != null)
{
// Do actual stuff.
}
}
}
I had the same issue and the ordering of the properties in XAML didn't help. In my case, I was binding ItemsSource to a property on a StaticResource, but I was binding SelectedIndex with a property of my page's ViewModel. The moment I changed the binding of ItemsSource to bind to a property on the ViewModel itself (i.e. duplicated a property of the StaticResource), my issue went away and I was able to perform 2-way binding on SelectedIndex as well.
I've found the same problem with my app.
But I noticed that it happens when I delete all the elements of the list bounded to the ListPicker in the ViewModel.
So it isn't necessary to Bind SelectedIndex with another property since the problem depends only on the list bounded.
Here is my code which work fine for me:
<toolkit:ListPicker x:Name="ListaCorsi"
SelectionChanged="ListaCorsi_SelectionChanged"
ItemsSource="{Binding ListaCorsiUser}"
SelectionMode="Single"
ItemTemplate="{StaticResource CorsiDataTemplate}"
ItemsPanel="{StaticResource ItemsPanelTemplateListaCorsi}"/>
The list in view model:
private ObservableCollection<Corsi> _listaCorsiUser;
public ObservableCollection<Corsi> ListaCorsiUser
{
get { return _listaCorsiUser; }
set
{
_listaCorsiUser = value;
OnPropertyChanged("ListaCorsiUser");
}
}
The handler for SelectionChanged:
void ListaCorsi_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (ListaCorsi.SelectedItem != null)
{
---
this.CorsoSelected = ListaCorsi.SelectedItem as Corsi;
}
}
Where Corsi is the class type of the list.
Here ListPicker template:
<DataTemplate x:Key="CorsiDataTemplate">
<Grid>
<Grid.Background>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="Black" Offset="0"/>
<GradientStop Color="#FF3523FF" Offset="0.25"/>
<GradientStop Color="Black" Offset="1"/>
<GradientStop Color="#FF3523FF" Offset="0.75"/>
</LinearGradientBrush>
</Grid.Background>
<TextBlock TextWrapping="Wrap" Text="{Binding NomeCorso}" FontSize="24" FontFamily="Freestyle Script" TextAlignment="Center"/>
</Grid>
</DataTemplate>
And, in the end, the method delete that checks if the list returned by IsolatedStorage is empty, if so, I put a fake empty element in the list bounded to the ListPicker, in order to not receive the error mentioned in this post.
if (this.CorsoSelected != null)
{
---
List<Corsi> corsi = new List<Corsi>(DBHelper.GetCorsiByUserId(PassaggioValori.UserId));
if (corsi.Count > 0)
{
this.ListaCorsiUser = new ObservableCollection<Corsi>(corsi);
}
else
{
this.ListaCorsiUser = new ObservableCollection<Corsi>(new List<Corsi>() { new Corsi()});
}
----
}
The strange thing was that, if the list was empty when the page has been loaded, nothing happens, instead, when I removed the last element from the list, the application raised the exception "SelectedItem must always be set to a valid value".
Now the problem is solved.