I have a listbox to which I'm binding HistoryItems , where HistoryItems is a ObservableCollection of History.
Here is the listbox declaration :
<ListBox x:Name="RecentListBox" SelectionChanged="RecentListBox_SelectionChanged" ItemsSource="{Binding HistoryItems,Converter={StaticResource HistoryValueConverter} }" ItemsPanel="{StaticResource ItemsPanelTemplate1_Wrap}" ItemTemplate="{StaticResource RecentViewModelTemplate}">
Here is the History class :
public class History : INotifyPropertyChanged
{
public History() { }
int _id;
string _date;
string _url;
string _name;
public History(int id, string date,string url,string name)
{
this.id = id;
this.date = date;
this.url = url;
this.name = name;
}
public int id
{
get
{
return _id;
}
set
{
if (value != _id)
{
_id = value;
NotifyPropertyChanged("id");
}
}
}
public string date
{
get
{
return _date;
}
set
{
if (!value.Equals(_date))
{
_date = value;
NotifyPropertyChanged("string");
}
}
}
public string url
{
get
{
return _url;
}
set
{
if (!value.Equals(_url))
{
_url = value;
NotifyPropertyChanged("url");
}
}
}
public string name
{
get
{
return _name;
}
set
{
if (!value.Equals(_name))
{
_name = value;
NotifyPropertyChanged("name");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (null != handler)
{
// App.viewModel.HistoryItems = (App.Current as App).dataHandler.retrieveHistory_DB();
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
When I start the app the list gets populated, but after I do some modifs in some pivot children, and go back to the main panorama view, I try to update the HistoryItems in OnNavigatedTo :
App.ViewModel.HistoryItems = (App.Current as App).dataHandler.retrieveHistory_DB();
but the listbox doesn't get updated (and the function returns the correct data). What could the problem be? History is INotifyPropertyChanged and the HistoryItems is a ObservableCollection<History> so there should be no problem.. What is causing the list to not update?
Since you are replacing HistoryItems when you refresh it doesn't matter that it's an ObservableCollection.
You can either clear the HistoryItems and then add the new items when you refresh. Or the ViewModel should implement INotifyPropertyChanged and the HistoryItems setter should raise the event.
Rewrite the setter for ViewModel.HistoryItems so that instead of doing this
_historyItems = value;
it does this
if (_historyItems == null)
_historyItems = new ObservableCollection<HistoryItem>();
_historyItems.Clear();
foreach (var hi in value)
_historyItems.Add(hi);
You need NotifyPropertyChanged for App.ViewModel in the Setter of HistoryItems
Related
I'm new to Xamarin Forms, I am trying to get/Pass the Id value from XAML UI to my ViewModel
My XAML:
TODO
My VM:
private int id;
public int Id
{
get
{
return id;
}
set
{
if (id != value)
{
id = value;
OnPropertyChanged("Id");
}
}
}
public string result { get; set; }
public ICommand SubmitResultsCommand
{
get
{
return new Command(async () =>
{
IsLoading = true;
Result _result = new Result();
var response
= await _services.SubmitResultsAsync(result, id, Settings.AccessToken);
IsLoading = false;
});
}
}
in ViewModel
Define the binding property which you need to bind to view in xaml
public class MyViewModel: INotifyPropertyChanged
{
// it is necessary if you want to change the value of Id in runtime
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private string id;
public string Id
{
get
{
return id;
}
set
{
if (id != value)
{
id = value;
NotifyPropertyChanged("Id");
}
}
}
// other properties
}
In ContentPage
Set the BindingContext
public MainPage()
{
InitializeComponent();
BindingContext = new MyViewModel();
}
My combo cbStudents is bound to StudentsList:
<ComboBox Name="cbStudents"
ItemsSource="{Binding Path=Students}"
SelectedItem="{Binding Path=SelectedStudent, Mode=TwoWay}"
DisplayMemberPath="Name"/>
public class Student
{
private string _name;
public string Name
{
get { return _name; }
set { _name = value; }
}
private int _age;
public int Age
{
get { return _age; }
set { _age= value; }
}
}
I want to get the SelectedItem:
I tried-
private ObservableCollection<Language> _students;
public ObservableCollection<Language> Students
{
get { return _students; }
set { _students= value; }
}
private string _selectedStudent;
public string SelectedStudent
{
get { return _selectedStudent; }
set { _selectedStudent= value; }
}
private void btnGetOutput(object sender, RoutedEventArgs e)
{
MessageBox.Show("Your selected item is: " + SelectedStudent);
}
Result:
I get Null output. No error code, nothing. Any help is appreciated.
It seems you want to select a student by its name, i.e. a string.
Instead of SelectedItem, you should then use SelectedValue and SelectValuePath:
<ComboBox
ItemsSource="{Binding Students}"
DisplayMemberPath="Name"
SelectedValuePath="Name"
SelectedValue="{Binding SelectedStudent}" />
The view model would of course have to implement INotifyPropertyChanged and should declare the Students property as a readonly:
public class ViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public ObservableCollection<Student> Students { get; }
= new ObservableCollection<Student>();
private string selectedStudent;
public string SelectedStudent
{
get { return selectedStudent; }
set
{
selectedStudent = value;
PropertyChanged?.Invoke(this,
new PropertyChangedEventArgs(nameof(SelectedStudent)));
}
}
}
First of all, you have defined ObservableCollection<Language> Students, I think it should be ObservableCollection<Student> Students instead.
Then, you have to bind to that collection, not to StudentList, which doesn't exist in your sample (maybe you didn't present full code?).
Then, you have to add items to that list somewhere, Students.Add(...).
Then, if items of your combo box are of type Student, then property bound to SelectedItem also must have type of Student, not string.
Last but not least: you have to bind class with all this fieelds defined to your view, so you must write: view.DataContext = objectWithData;, where view is your view and objectWithData is object with those fields defined.
You can implement INotifyPropertyChanged interface. As in the example below:
public class Data : INotifyPropertyChanged
{
// boiler-plate
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
protected bool SetValue<T>(ref T field, T value, string propertyName)
{
if (EqualityComparer<T>.Default.Equals(field, value)) return false;
field = value;
OnPropertyChanged(propertyName);
return true;
}
private ObservableCollection<Language> _students;
public ObservableCollection<Language> Students
{
get { return _students; }
set { _students= value; }
}
private Language _selectedStudent;
public Language SelectedStudent
{
get { return _selectedStudent; }
set { SetValue(_selectedStudent, value, "SelectedStudent"); }
}
}
I have to change the value in a text box dynamically, on selecting a value from a combox box, which is present in different view. when changing the dependency property's source, the propertychangedEventHandler value is not changing, i.e it is remaining as null, so the event is not getting fired. As a result the text in the textbox is not changing. Below is the code. I have bound the text in textbox to _name property.
public partial class Details : UserControl, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public string name = "";
public Details()
{
InitializeComponent();
Name = Connector.Name;
DataContext = this;
}
public string Name
{
get { return name; }
set
{
name = value; OnPropertyChanged("Name");
}
}
protected void OnPropertyChanged(string s)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(s));
}
}
}
Xaml code
<StackPanel Orientation="Vertical">
<TextBlock Text="Student Details" VerticalAlignment="Top" HorizontalAlignment="Center" FontSize="16" FontWeight="Bold"> </TextBlock>
<StackPanel Margin="0,5" Orientation="Horizontal" >
<Label MinWidth="100" MaxWidth="110">Name:</Label>
<Border BorderBrush="Gray" BorderThickness="2">
<TextBox Name="nametextbox" Text="{Binding Name,Mode=TwoWay}" Width="auto" MinWidth="100" FontWeight="Black"></TextBox>
</Border>
</StackPanel>
Is it possible that you accidentally exchanged name and _name, using name in XAML for the binding?
Usually you have a public property with a capitalized name, and a private field with a non-capitalized name, optionally prefixed with an underscore as you did.
So, you should have
public string Name {
get { return _name; }
set { _name = value; OnPropertyChanged("Name"); }
{
private string _name = "";
Please check the following:
If you're not currently binding to name instead of _name;
Either if that is or is not the case, please fix your naming convention, because it is a source of errors, and every example you'll find follow the convention I included above.
In your XAML, you are binding "Name" property and in your code, you have created _name property. So, you need to change it to "Name" property in your code.
Just change your property as per below:
private string _name = "";
public string Name
{
get { return _name; }
set {
_name = value;
OnPropertyChanged("Name");
}
}
Try this and let me know.
I have used eventaggregator for this purpose, as we need to change the text in the text box dynamically when an event in a different view is fired. Below is the C# code of both the DropView(where we select student name from a list), and DetailsView(where we display the details). I publish events in Drop.xaml.cs and subscribe to those events in Details.xaml.cs
Drop.xaml.cs
public partial class Drop : UserControl
{
private IEventAggregator iEventAggregator;
public Drop(IEventAggregator ieventaggregator)
{
InitializeComponent();
iEventAggregator = ieventaggregator;
this.DataContext = this;
var doc = XDocument.Load("C:\\Users\\srinivasaarudra.k\\Desktop\\students.xml");
var names = doc.Descendants("Name");
foreach (var item in names)
{
droplist.Items.Add(item.Value);
}
}
public string name;
public string Naam
{
get { return name; }
set { name = value;
iEventAggregator.GetEvent<Itemselectedevent>().Publish(Naam);
}
}
public string grade;
public string Grade
{
get { return grade; }
set
{
grade = value;
iEventAggregator.GetEvent<gradeevent>().Publish(Grade);
}
}
public string dept;
public string Dept
{
get { return dept; }
set
{
dept = value;
iEventAggregator.GetEvent<deptevent>().Publish(Dept);
}
}
public static string str;
public static string Str
{
get { return str; }
set {
str = value;
}
}
private void droplist_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var sel = droplist.SelectedValue;
Str=sel.ToString();
XmlDocument doc2 = new XmlDocument();
doc2.Load("C:\\Users\\srinivasaarudra.k\\Desktop\\students.xml");
var details = doc2.DocumentElement.SelectNodes("/Students/StudentDetails");
foreach (XmlNode node in details)
{
if (node.SelectSingleNode("Name").InnerText == Str)
{
Naam = node.SelectSingleNode("Name").InnerText;
Grade = node.SelectSingleNode("Grade").InnerText;
Dept = node.SelectSingleNode("Department").InnerText;
}
}
// Details det = new Details();
Details dt = new Details(iEventAggregator);
}
}
public class Itemselectedevent:Prism.Events.PubSubEvent<string>
{
}
public class gradeevent : Prism.Events.PubSubEvent<string>
{
}
public class deptevent : Prism.Events.PubSubEvent<string>
{
}
Details.xaml.cs
public partial class Details : UserControl,INotifyPropertyChanged
{
public IEventAggregator iEventAggregator;
public event PropertyChangedEventHandler PropertyChanged;
public static string name;
public static string dept;
public static string grade;
[Bindable(true)]
public string Naam
{
get { return name; }
set
{
name = value;
OnPropertyChanged("Naam");
}
}
[Bindable(true)]
public string Grade
{
get { return grade; }
set
{
grade = value; OnPropertyChanged("Grade");
}
}
[Bindable(true)]
public string Dept
{
get { return dept; }
set
{
dept = value;
OnPropertyChanged("Dept");
}
}
public Details(IEventAggregator eventaggregator)
{
InitializeComponent();
this.iEventAggregator = eventaggregator;
iEventAggregator.GetEvent<Itemselectedevent>().Subscribe((str) => { Naam = str; });
iEventAggregator.GetEvent<gradeevent>().Subscribe((str) => { Grade = str; });
iEventAggregator.GetEvent<deptevent>().Subscribe((str) => { Dept = str; });
this.DataContext = this;
}
protected void OnPropertyChanged(string s)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(s));
}
}
private void Button_Click_1(object sender, RoutedEventArgs e)
{
Application.Current.Shutdown();
}
}
I have an ObservableCollection<Person> in my viewmodel. This is bound as an ItemsSource to a DataGrid in the view. The class Person only has threeProperties:
public class Person : ViewModelBase
{
private Guid id;
public Guid Id
{
get { return this.id; }
set
{
this.id = value;
OnPropertyChanged("Id");
}
}
private string firstname;
public string Firstname
{
get { return this.firstname; }
set
{
this.firstname = value;
OnPropertyChanged("Firstname");
}
}
private string lastname;
public string Lastname
{
get { return this.lastname; }
set
{
this.lastname = value;
OnPropertyChanged("Lastname");
}
}
}
The class ViewModelBase implements INotifyPropertyChanged.
The items in the collection are updated perfect if I add or remove an entry in the dategrid. The item is then also removed in the collection.
My problem is that the content of an person-item is updated, but I don't know how I can react on this.
Do I have to add an event or something else to the person-class to get informed or is there another way to do this?
Implement INotifyPropertyChanged interface on your class Person so that any change in Person properties gets reflected back on UI.
Sample -
public class Person : INotifyPropertyChanged
{
private Guid id;
public Guid Id
{
get { return id; }
private set
{
if(id != value)
{
id = value;
NotifyPropertyChanged("Id");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Im new to WPF and Iv been breaking my head over this for past couple of days. I am trying to set a basic binding of textbox to a string property. I followed the MS tutorial but nothing seems to be working.
Here's email class, I am trying to bind its subject property to display in a textbox
public class Email : INotifyPropertyChanged
{
private string _subject;
public string Subject
{
get { return _subject; }
set
{
_subject = value;
OnPropertyChanged("Subject");
}
}
private string _contents;
public string Contents
{
get { return _contents; }
set
{
_contents = value;
OnPropertyChanged("Contents");
}
}
private Category _category;
public Category Category
{
get { return _category; }
set
{
_category = value;
OnPropertyChanged("Category");
}
}
public Email()
{
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string info)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(info));
}
}
}
Here's the email setter inside UserControl that parents the textbox:
private Email _email;
public Email Email
{
get { return _email; }
set
{
_email = value;
if (_email != null)
{
Binding myBinding = new Binding("Subject");
myBinding.Source = _email;
tbSubject.SetBinding(TextBlock.TextProperty, myBinding);
}
}
}
tbSubject is never getting set to anything, its always empty even if email passed is not null and has a subject! If I do just this:
public Email Email
{
get { return _email; }
set
{
_email = value;
if (_email != null)
{
tbSubject.Text = _email.Subject;
}
}
}
it works fine. I dont understand what I am doing wrong.
I think I've got it. Here's the change I had to make:
public partial class EmailContentsTemplate : UserControl, INotifyPropertyChanged
{
private Email _email;
public Email Email
{
get { return _email; }
set
{
_email = value;
OnPropertyChanged("Email");
}
}
public EmailContentsTemplate()
{
InitializeComponent();
DataContext = this;
Binding myBinding = new Binding("Email.Subject");
myBinding.Source = this;
tbSubject.SetBinding(TextBlock.TextProperty, myBinding);
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string info)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(info));
}
}
}
So I changed source to "this" and made the user control implement INotifyPropertyChanged. Now it works.
Alternatively I got it working through XAML
<TextBox x:Name="tbSubject" Grid.Column="1" Grid.Row="1" Margin="3" Text="{Binding Email.Subject}"/>