For handling Button Click in View-model we hook Button-Command with a ViewModel Property.
<Button Command="ButtonCommand"/>
class MyViewModel
{
ICommand _buttonCommand;
public MyViewModel()
{
_buttonCommand=new CommandHandler(() => Buttonfunction(), "true");
}
public ICommand ButtonCommand
{
get{ return _buttonCommand;}
}
private void Buttonfunction
{ //do something. }
}
public class CommandHandler : ICommand
{
private Action _action;
private bool _canExecute;
public CommandHandler(Action action, bool canExecute)
{
_action = action;
_canExecute = canExecute;
}
public bool CanExecute(object parameter)
{
return _canExecute;
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
_action();
}
}
Similarly What can be done for TextBox events.
How can we Bind a Command with TextBox Event in .NET 3.5.
<TextBox TextChanged=?/>
You must bind it to a property first, Then use the setter of that property as your text change event.
In your xaml:
<TextBox Text="{Binding Name}" />
In your Viewmodel
private string _name;
public string Name
{
get
{
return _name;
}
set
{
_name = value;
yourTextChangeEvent();
}
}
Related
Binding command to a Button - yields no effect (Xamarin, MVVM):
notes:
Pressing the Button and nothing happens: no CanExecute check occur.
Binding a Button in a ContentPage which is Part of a Tabbed-Template
functionality check and the rest of related MVVM binding works well: Defined a clicked-event and manually triggered the command from the code behind.
//Could someone see the reason?// editted
editted, new:
What would be a good practice when CanExecute relies on fields of a compound data type that are updated independently ? (*can take of the command parameter which is the compound data type, which is accessible to the command directly through the VM).
xaml for the View:
<ContentPage.Content>
<StackLayout>
<Entry Placeholder="Notes"/>
<Entry x:Name="courseIDEntry"
Text="{Binding CourseID, Mode=TwoWay}"
IsReadOnly="{Binding !ExistUnit}"
Placeholder="CourseID *"/>
<Entry x:Name="unitIDEntry"
Text="{Binding UnitID, Mode=TwoWay}"
IsReadOnly="{Binding !ExistUnit}"
Placeholder="UnitID *"/>enter code here
<Label Text="* Fields are mandatory"/>
<Button x:Name="AddSave"
Text="{Binding CommandText}"
Command="{Binding AddSaveCMD}"
CommandParameter="{Binding EdittedUnit}"/>
<!--Clicked="AddSave_Clicked"/>-->
</StackLayout>
</ContentPage.Content>enter code here
c# code behind for the view (*including the Button-Clicked check for)
public partial class EditUnitPage : ContentPage
{
EditUnitViewModel editUVM;
public EditUnitPage()
{
InitializeComponent();
editUVM = new EditUnitViewModel();
BindingContext = editUVM;
}
public EditUnitPage(Unit6 unitSelected) : this()
{
if (unitSelected != null)
{
editUVM.EdittedUnit = unitSelected;
editUVM.ExistUnit = true;
}
}
protected override void OnAppearing()
{
base.OnAppearing();
}
//private void AddSave_Clicked(object sender, EventArgs e)
//{
// if (editUVM.AddSaveCMD.CanExecute(editUVM.EdittedUnit))
// {
// editUVM.AddSaveCMD.Execute(null);
// }
//}
}
C# MyCommand (newbie. using ICommand and not the Command Class)
public class AddSaveUnitCommand : ICommand
{
public EditUnitViewModel EditUVM { get; set; }
public event EventHandler CanExecuteChanged;
public AddSaveUnitCommand(EditUnitViewModel euvm)
{
EditUVM = euvm;
}
public bool CanExecute(object parameter)
{
var editted = parameter as Unit6;
if (editted != null )
{
if (!string.IsNullOrEmpty(editted.CourseID) || !string.IsNullOrEmpty(editted.UnitID))
return true;
}
return false;
}
public void Execute(object parameterf)
{
EditUVM.AddSaveUnitAsync();
}
}
c# for VM (BaseViewModel implements INotify)
public class EditUnitViewModel : BaseViewModel
{
public AddSaveUnitCommand AddSaveCMD { get; set; }
private Unit6 edittedUnit;
public Unit6 EdittedUnit
{
get { return edittedUnit; }
set { edittedUnit = value; OnPropertyChanged(); }
}
private bool existUnit;
public bool ExistUnit
{
get { return existUnit; }
set
{
existUnit = value;
//OnPropertyChanged();
}
}
public string CommandText
{
get { return ExistUnit? "Save": "Add"; }
}
public string CourseID
{
get { return EdittedUnit.CourseID; }
set { EdittedUnit.CourseID = value; OnPropertyChanged(); }
}
public string UnitID
{
get { return EdittedUnit.UnitID; }
set { EdittedUnit.UnitID = value; OnPropertyChanged(); }
}
public EditUnitViewModel()
{
EdittedUnit = new Unit6();
AddSaveCMD = new AddSaveUnitCommand(this);
}
public async void AddSaveUnitAsync()
{
var curPage = App.Current.MainPage;
try
{
switch (ExistUnit)
{
case false: //insert new unit to the DB
EdittedUnit.UnitKey = ""; //Todo: look for more elegant of assigning auto value to property
Unit6.Insert(EdittedUnit);
break;
case true: //update details on existing unit
EdittedUnit.UnitKey = ""; //Todo: look for more elegant of assigning auto value to property
Unit6.Update(EdittedUnit);
break;
}
await curPage.DisplayAlert("Success", "Unit was succesffuly updateded", "OK");
}
catch
{
await curPage.DisplayAlert("Error", "Unit was not updated", "OK");
}
finally
{
EdittedUnit = null;
await curPage.Navigation.PushAsync(new MyTabbedPage());
}
}
}
xaml for the TabbedPage:
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:views="clr-namespace:P205.Views"
x:Class="P205.Views.MyTabbedPage">
<views:UnitsPage Title="Units" />
<views:EditUnitPage x:Name="editOrAddUnit" Title="Edit U"/>
<views:DBChangesPage Title="Edit DB"/>
<views:CoursesPage Title="Course"/>
<ContentPage Padding="10">
</ContentPage>
When your ViewModel defines a property of type ICommand, the ViewModel must also contain or reference a class that implements the ICommand interface. This class must contain or reference the Execute and CanExecute methods, and fire the CanExecuteChanged event whenever the CanExecute method might return a different value.
So you could try change like below:
public class AddSaveUnitCommand : ICommand
{
public EditUnitViewModel EditUVM { get; set; }
public event EventHandler CanExecuteChanged;
public AddSaveUnitCommand(EditUnitViewModel euvm)
{
EditUVM = euvm;
}
public bool CanExecute(object parameter)
{
var editted = parameter as Unit6;
if (editted != null )
{
if (!string.IsNullOrEmpty(editted.CourseID) || !string.IsNullOrEmpty(editted.UnitID))
return true;
}
return false;
}
public void Execute(object parameterf)
{
EditUVM.AddSaveUnitAsync();
CanExecuteChanged?.Invoke(this, EventArgs.Empty); //add this line.
}
}
I have been trying to bind my ListView to my View model. The view model successfully retrieves 5 records from the database and the Listview seems to display 5 blank rows, however it is not showing binding for each field within each row.
I have spent a couple of days searching internet but I don't seem to be doing anything different. I was using master detail pages so I thought that it may be the issue so I set my Events page as first navigation page without master/detail scenario but to no avail. Please note that I am using Portable Ninject for my dependencies/IoC.
My App.Xamal.cs is is as follows:
public App (params INinjectModule[] platformModules)
{
InitializeComponent();
var eventsPage = new NavigationPage(new EventsPage());
//Register core services
Kernel = new StandardKernel(new MyAppCoreModule(), new MyAppNavModule(eventsPage.Navigation));
//Register platform specific services
Kernel.Load(platformModules);
//Get the MainViewModel from the IoC
eventsPage.BindingContext = Kernel.Get<EventsViewModel>();
((BaseViewModel)(eventsPage.BindingContext)).Init();
MainPage = eventsPage;
}
My EventsPage.Xaml is provided below:
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MyApp.Views.EventsPage"
Title="Events">
<ContentPage.Content>
<ListView x:Name="Events" ItemsSource="{Binding Events}" >
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Label Text="{Binding EventID}" BackgroundColor="Red" TextColor="White"
FontAttributes="Bold" />
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</ContentPage.Content>
</ContentPage>
My EventsPage.xaml.cs is provided below:
namespace MyApp.Views
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class EventsPage : ContentPage, IBaseViewFor<EventsViewModel>
{
public EventsPage ()
{
InitializeComponent ();
}
EventsViewModel _vm;
public EventsViewModel ViewModel
{
get => _vm;
set
{
_vm = value;
BindingContext = _vm;
}
}
}
}
My EventsViewModel is as follows, it successfully retrieves 5 records and OnPropertyChanged is fired for Events property:
namespace MyApp.ViewModels
{
public class EventsViewModel : BaseViewModel, IBaseViewModel
{
ObservableCollection<Event> _events;
readonly IEventDataService _eventDataService;
public ObservableCollection<Event> Events
{
get { return _events; }
set
{
_events = value;
OnPropertyChanged();
}
}
public EventsViewModel(INavService navService, IEventDataService eventDataService) : base(navService)
{
_eventDataService = eventDataService;
Events = new ObservableCollection<Event>();
}
public override async Task Init()
{
LoadEntries();
}
async void LoadEntries()
{
try
{
var events = await _eventDataService.GetEventsAsync();
Events = new ObservableCollection<Event>(events);
}
finally
{
}
}
}
}
My BaseViewModel is as follows:
namespace MyApp.ViewModels
{
public abstract class BaseViewModel : INotifyPropertyChanged
{
protected INavService NavService { get; private set; }
protected BaseViewModel(INavService navService)
{
NavService = navService;
}
bool _isBusy;
public bool IsBusy
{
get
{
return _isBusy;
}
set
{
_isBusy = value;
OnPropertyChanged();
OnIsBusyChanged();
}
}
protected virtual void OnIsBusyChanged()
{
}
public abstract Task Init();
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
// Secod BaseViewModel abstract base class with a generic type that will be used to pass strongly typed parameters to the Init method
public abstract class BaseViewModel<TParameter> : BaseViewModel
{
protected BaseViewModel(INavService navService) : base(navService)
{
}
public override async Task Init()
{
await Init(default(TParameter));
}
public abstract Task Init(TParameter parameter);
}
}
IBaseViewModel is just a blank interface:
public interface IBaseViewModel
{
}
IBaseViewFor is given below:
namespace MyApp.ViewModels
{
public interface IBaseViewFor
{
}
public interface IBaseViewFor<T> : IBaseViewFor where T : IBaseViewModel
{
T ViewModel { get; set; }
}
}
My Event model is as follows:
namespace MyApp.Models
{
public class Event
{
public int EventID;
}
}
Finally, the image of the output, as you can see that 5 rows are created with red background but EventID is not binding in each row. I have checked the data and EventID is returned. I have even tried to manually add records into Events list but to no avail, see the manual code and image below:
async void LoadEntries()
{
try
{
Events.Add((new Event() { EventID = 1 }));
Events.Add((new Event() { EventID = 2 }));
Events.Add((new Event() { EventID = 3 }));
Events.Add((new Event() { EventID = 4 }));
Events.Add((new Event() { EventID = 5 }));
}
finally
{
}
}
I have spent a lot of time on it but unable to find a reason for this anomaly, can someone please cast a fresh eye and provide help!?
You can only bind to public properties - ie, you need a getter
public class Event
{
public int EventID { get; set; }
}
I have a custom checkbox control that I created with an ICommand property and the corresponding bindable property (my checkbox is a Xamarin.Forms XAML Page), the code is:
CheckBox.xaml
<Image x:Name="imgCheckBox"
WidthRequest="20"
HeightRequest="20"/>
<Label x:Name="lblCheckBox"
TextColor="Black"
VerticalOptions="CenterAndExpand"/>
<TapGestureRecognizer Tapped="OnCheckBoxTapped"/>
CheckBox.xaml.cs
public partial class CheckBox : ContentView
{
private static ImageSource uncheckedImage;
private static ImageSource checkedImage;
public CheckBox()
{
InitializeComponent();
uncheckedImage = ImageSource.FromResource("cbUnchecked.png");
checkedImage = ImageSource.FromResource("cbChecked.png");
imgCheckBox.Source = uncheckedImage;
}
public static readonly BindableProperty IsCheckedProperty =
BindableProperty.Create<CheckBox, bool>(
checkbox =>
checkbox.IsChecked,
false,
propertyChanged: (bindable, oldValue, newValue) =>
{
CheckBox checkbox = (CheckBox)bindable;
EventHandler<bool> eventHandler = checkbox.CheckedChanged;
if (eventHandler != null)
{
eventHandler(checkbox, newValue);
}
});
public bool IsChecked
{
set { SetValue(IsCheckedProperty, value); }
get { return (bool)GetValue(IsCheckedProperty); }
}
void OnCheckBoxTapped(object sender, EventArgs args)
{
IsChecked = !IsChecked;
if (IsChecked)
{
imgCheckBox.Source = checkedImage;
}
else
{
imgCheckBox.Source = uncheckedImage;
}
}
public static readonly BindableProperty CheckBoxCommandProperty =
BindableProperty.Create<CheckBox, ICommand>(
checkbox =>
checkbox.CheckBoxCommand,
null,
BindingMode.TwoWay,
propertyChanged: (bindable, oldValue, newValue) =>
{
CheckBox checkbox = (CheckBox)bindable;
EventHandler<bool> eventHandler = checkbox.CheckedChanged;
if (eventHandler != null)
{
eventHandler(checkbox, checkbox.IsChecked);
}
});
public event EventHandler<bool> CheckedChanged;
public ICommand CheckBoxCommand
{
get { return (ICommand)GetValue(CheckBoxCommandProperty); }
set { SetValue(CheckBoxCommandProperty, value); }
}
}
This checkbox implementation is on another Page called TermsAndConditionsPage, that is also a a Xamarin.Forms XAML Page, the code of the implementation is:
<toolkit:CheckBox Text="{Binding txtCheckBox}"
FontSize="Small"
CheckBoxCommand="{Binding OnCheckBoxTapChanged}"
IsChecked="{Binding IsCheckedChanged, Mode=TwoWay}"/>
<Button Text="Next"
Command="{Binding Next_OnClick}"
IsEnabled="{Binding Next_IsEnabled}"
HorizontalOptions="CenterAndExpand"
Clicked="OnNextClicked"/>
The Code Behind of this page is empty (Constructur with InitializeComponent()).
I also have the ViewModel of this page with this code:
TermsAndConditionsViewModel.cs
private string _txtCheckBox;
public string txtCheckBox
{ get { return _txtCheckBox; }
set
{
_txtCheckBox = value;
OnPropertyChanged("txtCheckBox");
}
}
private bool _Next_IsEnabled;
public bool Next_IsEnabled
{
get { return _Next_IsEnabled; }
set
{
_Next_IsEnabled = value;
OnPropertyChanged("Next_IsEnabled");
}
}
private bool _IsCheckedChanged;
public bool IsCheckedChanged
{
get { return _IsCheckedChanged; }
set
{
_IsCheckedChanged = value;
OnPropertyChanged("IsCheckedChanged");
}
}
public ICommand Next_OnClick { get; set; }
public ICommand OnCheckBoxTapChanged { get; set; }
public TermsAndConditionsViewModel()
{
txtCheckBox = "I agree with the terms and conditions";
Next_OnClick = new Command(NextClicked);
OnCheckBoxTapChanged = new Command(CheckBoxTapped);
}
private void CheckBoxTapped()
{
if (IsCheckedChanged)
{ Next_IsEnabled = true; }
else
{ Next_IsEnabled = false; }
}
private void NextClicked()
{ App.Current.MainPage = new Views.HelloWorld(); }
#region INPC
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{ PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); }
}
public event PropertyChangedEventHandler PropertyChanged;
#endregion
Now, the question time: the problem I'm having is the CheckBoxTapped Command is not working, I mean, it doesn't do anything, although the checkbox image changes every time I touch it, it does not change the Next_IsEnabled property of my button. I'd like to know what I am missing here to make this command work properly.
EDIT
What I'm looking for is a Command that behaves similarly to the one that Buttons have.
Thanks all for your time!
Since the original answer is now obsolete, here is the new method:
using System.Windows.Input;
public partial class MyControlExample : ContentView
{
// BindableProperty implementation
public static readonly BindableProperty CommandProperty =
BindableProperty.Create(nameof(Command), typeof(ICommand), typeof(MyControlExample), null);
public ICommand Command
{
get { return (ICommand)GetValue(CommandProperty); }
set { SetValue(CommandProperty, value); }
}
// Helper method for invoking commands safely
public static void Execute(ICommand command)
{
if (command == null) return;
if (command.CanExecute(null))
{
command.Execute(null);
}
}
public MyControlExample()
{
InitializeComponent();
}
// this is the command that gets bound by the control in the view
// (ie. a Button, TapRecognizer, or MR.Gestures)
public Command OnTap => new Command(() => Execute(Command));
}
Something like that (pseudocode):
public class YourClassName : View
{
public YourClassName()
{
var gestureRecognizer = new TapGestureRecognizer();
gestureRecognizer.Tapped += (s, e) => {
if (Command != null && Command.CanExecute(null)) {
Command.Execute(null);
}
};
var label = new Label();
label.GestureRecognizers.Add(gestureRecognizer);
}
public static readonly BindableProperty CommandProperty =
BindableProperty.Create<YourClassName, ICommand>(x => x.Command, null);
public ICommand Command
{
get { return (ICommand)GetValue(CommandProperty); }
set { SetValue(CommandProperty, value); }
}
}
I'm trying to make good use of ReactiveList and I think I'm close.
My expectation is that only "toyota" is shown after the user presses the filter button
XAML (yes, quick n dirty, no command for the Filter)
<Window
x:Class="WpfApplication1.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">
<StackPanel>
<ComboBox
ItemsSource="{Binding Path=CarsVM}"
DisplayMemberPath="Name" />
<Button
Click="ButtonBase_OnClick">
Filter
</Button>
</StackPanel>
</Window>
The code
using System.Windows;
using ReactiveUI;
namespace WpfApplication1
{
public partial class MainWindow
{
private readonly ViewModel _viewModel;
public MainWindow()
{
InitializeComponent();
_viewModel = new ViewModel();
DataContext = _viewModel;
}
private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
_viewModel.ChangeFilter();
}
}
}
public class CarViewModel : ReactiveObject
{
private bool _isVisible = true;
public CarViewModel(string name)
{
Name = name;
}
public bool IsVisible
{
get { return _isVisible; }
set
{
_isVisible = value;
this.RaiseAndSetIfChanged(ref _isVisible, value);
}
}
public string Name { get; set; }
}
public class ViewModel
{
private readonly ReactiveList<CarViewModel> _cars = new ReactiveList<CarViewModel>
{
new CarViewModel("bmw"),
new CarViewModel("toyota"),
new CarViewModel("opel")
};
public ViewModel()
{
_cars.ChangeTrackingEnabled = true;
CarsVM = _cars.CreateDerivedCollection(x => x, x => x.IsVisible);
}
public IReactiveDerivedList<CarViewModel> CarsVM { get; set; }
public void ChangeFilter()
{
foreach (var car in _cars)
{
car.IsVisible = car.Name.Contains("y");
}
}
}
Your bug is in the setter of IsVisible. By pre-assigning the value of _isVisible, RaiseAndSetIfChanged always thinks that the value has never changed. Remove _isVisible = value; and everything should work.
I am a little lost in how to use the CommandParameter in XAML. I am trying to bind a TextBox and a Button.
This my XAML code:
<TextBox x:Name="txtCity" Height="70"
VerticalAlignment="Top"/>
<Button x:Name="btnCity"
Content="Get"
Background="CornflowerBlue"
Height="70"
Command="{Binding GetweatherCommand}"
CommandParameter="{Binding ElementName=txtCity, Path=Text}"/>
In my ViewModel class I have the following to handle the clic action:
ActionCommand getWeatherCommand; //ActionCommand derivides from ICommand
public ActionCommand GetWeatherCommand
{
get
{
if (getClimaCommand != null)
{
getClimaCommand = new ActionCommand(() =>
{
serviceModel.getClima("????");
});
}
return getWeatherCommand;
}
}
My ActionCommand class:
public class ActionCommand : ICommand
{
Action action;
public ActionCommand(Action action)
{
this.action = action;
}
public bool CanExecute(object parameter)
{
return true;
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
action();
}
}
When I debug, the parameters in the Execute and CanExecute methods have the proper value. However, I guess the problem is in the method from the ViewClass (GetWeatherCommand). I can't figure out how to pass the parameter.
So, based on the above, does anyone know how can I pass the parameter to the method that will be executed?
ActionCommand.Execute is ignoring the command parameter. Try this:
public class ActionCommand<TParam> : ICommand
{
Action<TParam> action;
public ActionCommand(Action<TParam> action)
{
this.action = action;
}
public bool CanExecute(object parameter)
{
return true;
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
action((TParam)parameter);
}
}
And then:
getClimaCommand = new ActionCommand<string>(param =>
{
serviceModel.getClima(param);
});