I am new to WPF. I have created a WPF project, and add the following class
public class MessageList:INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
private List<string> list = new List<string>();
public List<string> MsgList
{
get { return list; }
set
{
list = value;
OnPropertyChanged("MsgList");
}
}
public void AddItem(string item)
{
this.MsgList.Add(item);
OnPropertyChanged("MsgList");
}
}
Then in the main window I added a ListBox and below is the xaml content
<Window.DataContext>
<ObjectDataProvider x:Name="dataSource" ObjectType="{x:Type src:MessageList}"/>
</Window.DataContext>
<Grid>
<Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="52,44,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
<ListBox Height="233" IsSynchronizedWithCurrentItem="True" HorizontalAlignment="Left" Margin="185,44,0,0" Name="listBox1" VerticalAlignment="Top" Width="260" ItemsSource="{Binding Path=MsgList}" />
</Grid>
Here is the source code of MainWindow.cs
public partial class MainWindow : Window
{
private MessageList mlist = null;
public MainWindow()
{
InitializeComponent();
object obj = this.DataContext;
if (obj is ObjectDataProvider)
{
this.mlist = ((ObjectDataProvider)obj).ObjectInstance as MessageList;
}
}
private void button1_Click(object sender, RoutedEventArgs e)
{
this.mlist.AddItem(DateTime.Now.ToString());
}
}
My question is after I clicked the button, there isn't any content displayed on the Listbox, what is the reason?
You should use an ObservableCollection instead of a List to notify the UI of collection changes.
You asked for a reason, while devdigital gave you the solution its worth mentioning why it is not working, and why his fix works:
Your mlist is bound to the ListBox and its all working well. Now you press the button and you add an entry to your list. The listbox just won't know about this change, because your list has no way of telling "Hey i just added a new item". To do that, you need to use a Collection implementing INotifyCollectionChanged, like the ObservableCollection. This is very similar to your OnPropertyChanged if you modify a property on your MessageList it also calls the OnPropertychanged method which fires the PropertyChanged event. The Databinding registers to the PropertyChanged event and now knows when you updated your property and automatically updates the UI. The same is necessary for Collections if you want this automatic updating of the UI on collections.
The culprit is the string items... string items being of primitive type, do not refresh bindings on the list box when you do the OnPropertyChanged
Either use observable collection or call this in your button1_Click() function...
listBox1.Items.Refresh();
Related
I'm trying to bind the data with text block in a listview but it doesn't show the data. However, when I run the application, I can see the list is created but it display the empty data. See the empty list of data in the below image:
Here's my XAML code:
<ListView Margin="20,0,0,20" x:Name="listView_attachedFiles">
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Width="100" Text="{Binding AttachedFiles, Mode=TwoWay, NotifyOnTargetUpdated=True}">
<Hyperlink>
</Hyperlink>
</TextBlock>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Here's the C# Code
public class ListviewModel : INotifyPropertyChanged
{
private ObservableCollection<string> _attachedfiles;
public ObservableCollection<string> AttachedFiles
{
get { return _attachedfiles; }
set
{
_attachedfiles = value;
OnPropertyChanged("AttachedFiles");
}
}
public ListviewModel()
{
AttachedFiles = new ObservableCollection<string>();
}
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Raises this object's PropertyChanged event.
/// </summary>
/// <param name="propertyName">The property that has a new value.</param>
protected void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Here's is how I'm populating the data:
// I'm calling this method to attach the list of filenames
private void ExecuteMethod_AttachFile(object Parameter)
{
OpenFileDialog ofd = new OpenFileDialog();
ofd.Multiselect = true;
if (ofd.ShowDialog() == true)
{
AttachedFileLocation = ofd.FileNames.ToList();
// adding bind data to the list of viewmodel: adding attachefile names
foreach (var file in AttachedFileLocation)
{
FileInfo info = new FileInfo(file);
DMS_Form.Instance.ListofViewModel.AttachedFiles.Add(info.Name + " X");
}
}
}
Here's is how I'm attaching the itemssource reference in the constructor of the WPF Form.
//Binding the list of attached files with the listview
listView_attachedFiles.ItemsSource = ListofViewModel.AttachedFiles;
Please help me figure out where I'm making the mistake. Any help would be highly appreciated. Thank you
Ali
With some hours of research, I realized there was a bit problem with my code. The solution is to first define data context in the WPF Form constructor method i.e
listView_attachedFiles.DataContext = ListofViewModel;
second update this XAML code
<TextBlock Width="100" Text="{Binding AttachedFiles, Mode=TwoWay, NotifyOnTargetUpdated=True}">
with this XAML code.
<TextBlock Width="100" Text="{Binding}">
Now save, and build the application, run it.
I have a problem binding to a WPF form . I have my own static "settings" class (singleton) that implements PropertyChangedEventHandler and raises the event whenever a property is updated.
The singleton object is added to resources in the form's constructor and the property is correctly read on form's initialization, thus suggesting that the binding is correct.
However, WPF does NOT register any event handler for PropertyChangedEventHandler and PropertyChanged is always null. Thus the event is never raised, and my form is never updated (it's meant to be updated on a button click).
What am I doing wrong?
I suspect that calling Resources.Add for some reason prevents WPF from registering its own event handler, but I'm not sure.
I've read multiple SO questions on similar topics, but the 2 most common issues are not creating a proper singleton (thus passing another instance to xaml then intended) or not implementing INotifyPropertyChanged. I'm doing both of these correctly.
Expected behavior:
Settings.TextValue is the property I'm interested in. In its setter, NotifyPropertyChanged is called, which unfortunately fails to raise this.PropertyChanged event, since WPF registers no handler.
When MainWindow.Button1 is click, the textBox's value is supposed to change to "ButtonA OK" from the initial value of Settings.TextBox ("testOK").
Here's the code:
Settings.cs:
namespace bindings
{
public sealed class Settings : INotifyPropertyChanged
{
private static readonly Settings instance = new Settings();
private Settings()
{
}
public static Settings Instance { get { return instance; } }
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName = null)
{
// passing propertyName=null raises the event for all properties
if (PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
private string textValue = "testOK";
public static string TextValue
{
get { return Instance.textValue; }
set { Instance.textValue = value; Instance.NotifyPropertyChanged(); }
}
}
MainWindow.xaml.cs
namespace bindings
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
Resources.Add("foobar", Settings.Instance);
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
}
private void button1_Click(object sender, RoutedEventArgs e)
{
int hash = Settings.Instance.GetHashCode();
Settings.TextValue = "ButtonA OK";
}
}
}
MainWindow.xaml
<Window x:Class="bindings.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" Loaded="Window_Loaded" WindowStyle="ToolWindow">
<Grid PresentationTraceSources.TraceLevel="High" DataContext="{StaticResource foobar}">
<Button Content="ButtonA" Height="33" HorizontalAlignment="Left" Margin="76,243,0,0" Name="button1" VerticalAlignment="Top" Width="101" Click="button1_Click" />
<TextBox Height="28" HorizontalAlignment="Left" Margin="182,180,0,0" Name="textBox1" VerticalAlignment="Top" Width="93"
Text="{Binding Path=TextValue, Mode=OneWay}" DataContext="{Binding}" PresentationTraceSources.TraceLevel="High"/>
</Grid>
</Window>
Thanks for help!
I appear to be having serious problems getting my WPF UI to update when I update when I update the property it is bound to. Here is my view model class definition:
namespace WpfModel
{
class AppModel : INotifyPropertyChanged
{
private int _count = 7;
public int Count { get { return _count; }
set { _count = value; OnPropertyChanged("Count"); } }
public void Increment()
{
Count++;
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string prop)
{
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
var e = new PropertyChangedEventArgs("prop");
handler(this, e);
}
}
};
}
This is bound to my simple UI in the following XAML:
<Window x:Class="WpfModel.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="clr-namespace:WpfModel"
Title="WPF Data Model Demo" Height="128" Width="284" >
<Window.DataContext>
<vm:AppModel />
</Window.DataContext>
<Grid Height="Auto" Width="Auto">
<Button Margin="0,0,12,12" Name="IncButton" Height="23" VerticalAlignment="Bottom" HorizontalAlignment="Right" Width="75" Click="IncButton_Click" Content="Increment" />
<Label Content="Count Variable:" Height="28" HorizontalAlignment="Left" Margin="12,12,0,0" Name="label1" VerticalAlignment="Top" />
<Label Height="28" Margin="116,12,0,0" Name="CountLabel" VerticalAlignment="Top" HorizontalAlignment="Left" Width="40" Content="{Binding Path=Count}" />
</Grid>
</Window>
The application is defined like follows:
namespace WpfModel
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
private AppModel _model = new AppModel();
public MainWindow()
{
InitializeComponent();
//_model = new AppModel();
}
private void IncButton_Click(object sender, RoutedEventArgs e)
{
}
}
}
When the app starts up, everything is peachy, the label even initially displays whatever value is in the Count property of the model. Calling increment updates the model properly, and directly incrementing the Count property as shown in the code also works just fine.
The problem here, is that the PropertyChanged event handler never seems to get added to. I can step through the code in the debugger and see the value in the property updating, and I can see the call to OnPropertyChanged even, but the PropertyChanged handler itself is always null.
Is there a problem with my binding maybe?
I am using MSVC 2010 Express.
The issue is that the WpfModel you have as an instance variable, _model, is not the same instance that's being used as the Window's DataContext. Thus, it is not bound to by anything, and its PropertyChanged will always be null.
Change your XAML for setting the datacontext to this:
<Window.DataContext>
<vm:AppModel x:Name="_model" />
</Window.DataContext>
Get rid of the instance variable declared in the code behind, and fix the OnPropertyChanged implementation (use the parameter instead of the literal string "prop"), and it works.
this line:
var e = new PropertyChangedEventArgs("prop");
should be:
var e = new PropertyChangedEventArgs(prop);
You are passing the string "prop" so the bound values listening for "Count" will not be triggered.
**EDIT **
Based on your other comments (Answer?) I thought I had better update this with a fix - you could use the answer already given of course but I dont want to copy someone else :).
Add this to your click handler:
((AppModel)this.DataContext).Count += 1;
I am trying to bind a list box to a collection. The problem is that the collection can change, but the collection doesn't implement IObservableCollection. What is the best way to force the binding to refresh?
As Tormod suggested, the preferable methods would be changing the collection to an ObservableCollection, or implementing INotifyCollectionChanged in the collection would take care of refreshing the UI.
However, if those options aren't available, then you can 'force' a refresh by using INotifyPropertyChanged in whatever class contains the collection. We then will be treating the list just like a regular property, and using the setter to notify on changes. To do this it requires re-assigning the reference, which is why using something like an ObservableCollection is preferred, as well as raising the PropertyChanged event.
Here is a quick sample showing how this can be done with just a standard generic List:
public partial class Window1 : Window, INotifyPropertyChanged
{
public Window1()
{
InitializeComponent();
this.Names = new List<string>() { "Mike", "Robert" };
this.DataContext = this;
}
private IList<string> myNames;
public IList<string> Names
{
get
{
return this.myNames;
}
set
{
this.myNames = value;
this.NotifyPropertyChanged("Names");
}
}
private void OnAddName(object sender, RoutedEventArgs e)
{
Names.Add("Kevin");
Names = Names.ToList();
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String info)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}
}
Xaml:
<Window x:Class="Sample.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>
<StackPanel>
<ListBox ItemsSource="{Binding Names}" />
<Button Content="Add Name"
Click="OnAddName" />
</StackPanel>
</Grid>
Without more information on how and where this collection is used, here are some pointers which may help you.
If the collection is not sealed, you could inherit it.
If the collection is sealed, you could create an adapter class which contains an instance of your collection and wraps all relevant methods.
In any case, your new class could implement IObservableCollection and be used for binding.
You can set a binding to update explicitly and then trigger an update through code by say having a refresh button for example.
As an example.
<StackPanel>
<ListBox
x:Name="lb"
ItemsSource="{Binding SomeList, UpdateSourceTrigger=Explicit}"
/>
<Button Content="Refresh" Click="Refresh_Click" />
</StackPanel>
private void Refresh_Click(object sender, RoutedEventArgs e)
{
BindingExpression be = lb.GetBindingExpression(ListBox.ItemsSourceProperty);
be.UpdateSource();
}
You can also force a refresh in your ViewModel. This is sth I've seen Josh Smith do in his MVVM demo app:
ICollectionView coll = CollectionViewSource.GetDefaultView(myCollection);
if (coll!=null)
coll.Refresh();
myCollection can be any type of collection that you have bound to the View.
Bea Stollnitz has a bit more information about CollectionViewSource:
http://www.beacosta.com/blog/?m=200608
I have a listbox with a bunch of contols in each list item.
<ListBox x:Name="projectList" IsSynchronizedWithCurrentItem="True">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding Name}" />
<ListBox x:Name="taskList" ItemsSource="{Binding Tasks}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding Name}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<TextBox x:Name="textBoxTask" />
<Button
x:Name="ButtonAddNewTask"
Content="Test"
CommandParameter="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=DataContext}"
Click="ButtonAddNewTask_Click"
/>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
When I click on the button in the listbox i want to add a new item to the listbox within the listbox. I've come this far. So my question is how do I get hold of the textbox and how do I update the listbox?
Here is my click event
private void ButtonAddNewTask_Click(object sender, RoutedEventArgs e)
{
Button button = (Button)sender;
Project proj = button.DataContext as Project;
if(proj.Tasks == null)
proj.Tasks = new List<Task>();
proj.Tasks.Add(new Task("Added Task"));
}
Thanx
The easiest solution would likely be to have one object represent each item in the outer ListBox. It would then have properties that would represent each control in the item - the text in the TextBox, and the items in the ListBox (a list of Tasks, I think, based on your Click handler).
In your Click handler, you can get the Button's DataContext (which should be an item in the collection of the outer list), and add a new Task to that object's list of tasks. Since the inner ListBox is bound to that list, it should be updated with the new item (assuming that it sends events when items are added, such as with ObservableCollection).
Update: Based on your comments, the following should work.
Your Project class should have two properties:
class Project
{
public string Name { get; set; }
private ObservableCollection<Task> tasks =
new ObservableCollection<Task>();
public IList<Task> Tasks
{
get { return this.tasks; }
}
}
The Task class just has one property - the name of the task.
The ProjectView class is a wrapper around the Project class (I got this idea from #timothymcgrath's answer). It keeps track of the name of a new task, and the current Project:
class ProjectView : INotifyPropertyChanged
{
public Project Project { get; set; }
private string newTaskName = string.Empty;
public string NewTaskName
{
get { return this.newTaskName; }
set
{
this.newTaskName = value;
this.OnPropertyChanged("NewTaskName");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propName)
{
PropertyChangedEventHandler eh = this.PropertyChanged;
if(null != eh)
{
eh(this, new PropertyChangedEventArgs(propName));
}
}
}
You'll need a new class that will be used as the DataContext. Something like this:
class Model
{
private ObservableCollection<ProjectView> projects =
new ObservableCollection<ProjectView>();
public IList<ProjectView> Projects
{
get { return this.projects; }
}
}
In the code behind, set the DataContext of the object to an instance of the above class:
public class Window1
{
public Window1()
{
this.InitializeComponent();
this.DataContext = this.model;
}
private Model model = new Model();
}
In the XAML, the bindings should be modified to bind to the above properties:
<ListBox x:Name="projectList" IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding Path=Projects}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding Project.Name}" />
<ListBox x:Name="taskList"
ItemsSource="{Binding Project.Tasks}"
DisplayMemberPath="Name" />
<TextBox x:Name="textBoxTask"
Text="{Binding Path=NewTaskName, UpdateSourceTrigger=PropertyChanged}"/>
<Button x:Name="ButtonAddNewTask" Content="Test"
Click="ButtonAddNewTask_Click" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Finally, in the click handler for the button, create the task. The DataContext of the Button will be the ProjectView for that item.
private void ButtonAddNewTask_Click(object sender, RoutedEventArgs e)
{
Button btn = (Button)sender;
ProjectView curProject = btn.DataContext as Project;
if(null != curProject)
{
curProject.Project.Tasks.Add(new Task()
{
Name = curProject.NewTaskName
});
}
}
Since all of the controls get their values via binding, you don't need to access the control itself to get the data - just use the data structures that are supplying the controls already.
It would probably be better to move the code that creates the Task into another class (possibly Project), but I just left it in the event handler for ease of typing on my part.
Update 2: Modified the above code to move the NewTaskName property into a separate class that wraps an instance of Project for use with the UI. Does this work better for you?
I'm assuming your Project ListBox is populated with an Collection of Project objects. I would add an AddNewTask ICommand to the Project class and expose it through a property. Then bind the Add New Task button to the new AddNewTask ICommand. For the CommandParameter, put the TaskName in and it will be passed into the command.
Try reading up on some MVVM (Model View ViewModel) for some examples of how this works. It is very clean and works great.
This solution worked for the task at hand so to speak.
private void ButtonAddNewTask_Click(object sender, RoutedEventArgs e)
{
Button button = (Button)sender;
DependencyObject obj = LogicalTreeHelper.GetParent(button);
StackPanel item = obj as StackPanel;
TextBox textBox = item.FindName("textBoxTask") as TextBox;
ListBox listBox = item.FindName("taskList") as ListBox;
Project proj = button.DataContext as Project;
if(proj.Tasks == null)
proj.Tasks = new List<Task>();
listBox.ItemsSource = proj.Tasks;
listBox.Items.Refresh();
}