I have the following code which used to work on Android just fine until MAUI Preview 9:
XAML:
<CollectionView ItemsSource="{Binding ViewModel_MyConns}">
<CollectionView.ItemTemplate>
<DataTemplate>
<Label Text="{Binding LastName}" TextColor="Red"/>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
MVVM code:
public class ConnsViewModel: INotifyPropertyChanged {
public ObservableCollection<STuser> ViewModel_MyConns { get; }
IList locallist;
// constructor:
public ConnsViewModel() {
ViewModel_MyConns = new ObservableCollection<STuser>();
locallist = ReadDataFromDB();
foreach (var item in locallist) {
ViewModel_MyConns.Add(item);
}
}
}
Everything used to work fine and I'd get the CollectionView updated with the values I read from the DB.
But now with MAUI Preview 9 this no longer works.
Any ideas/theories/solutions?
Thanks.
(P.S. Since I'm working with an ObservableCollection, there's no need to raise the PropertyChanged event. But in a desperate attempt to make it work, I fired PropertyChanged all the same, but to no avail).
Related
The code below shows a simple example of a CollectionView. I am not receiving the event for the SelectionChangedCommand. Can someone see what I am doing wrong?
btw, the complete source for this can be found on GitHub here.
MainPage.xaml
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:ControlDemo"
x:Class="ControlDemo.MainPage">
<StackLayout>
<CollectionView SelectionMode ="Single"
ItemsSource="{Binding Tags}"
SelectionChangedCommand="{Binding SelectedTagChanged}">
<CollectionView.ItemTemplate>
<DataTemplate>
<StackLayout>
<Label Text="{Binding .}" />
</StackLayout>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</StackLayout>
</ContentPage>
MainPageModel.cs
public class MainPageModel : FreshBasePageModel
{
public override void Init(object initData)
{
Tags = new List<string>() { "A", "B", "C" };
base.Init(initData);
}
public List<string> Tags { get; set; }
public Command SelectedTagChanged
{
get
{
return new Command(() =>
{
});
}
}
}
Couple of things that worked at my side (additionally to the SelectionMode = Single):
Make sure your Command' signature is <object> at your PageModel and do any cast according to your needs (specially if your collection becomes more complex).
Also at your XAML you want to give your CollectionView a name and use the SelectedItem property.
SelectionChangedCommandParameter="{Binding SelectedItem, Source={x:Reference cvTagsCollectionView}}"
I use your code and created a demo on my side, I add the widthRequest and HeightRequest to make the collectionView work:
<CollectionView
HeightRequest="170"
WidthRequest="200"
SelectionMode="Single"
SelectionChangedCommand="{Binding SelectedTagChangedCommand}"
ItemsSource="{Binding Tags}"
>
The SelectionChangedCommand did triggered after I click different items in the CollectionView.
I uploaded a sample here and you can check it: collectionView-selectItemChanged-xamarin.forms
If you want to use your ViewModel, then you should use the Binding for the SelectedItem:
<CollectionView ItemsSource="{Binding Monkeys}"
SelectionMode="Single"
SelectedItem="{Binding SelectedMonkey, Mode=TwoWay}">
...
</CollectionView>
and, in your ViewModel:
Monkey selectedMonkey;
public Monkey SelectedMonkey
{
get
{
return selectedMonkey;
}
set
{
if (selectedMonkey != value)
{
selectedMonkey = value;
}
}
}
So everytime you select a new object, the SelectedMonkey will be updated.
If you want to track the SelectionChanged, then, it should be in the code-behind (not sure how to implement within the viewmodel, nothing about that in the docs)
<CollectionView ItemsSource="{Binding Monkeys}"
SelectionMode="Single"
SelectionChanged="OnCollectionViewSelectionChanged">
...
</CollectionView>
And, in your Page.xaml.cs:
void OnCollectionViewSelectionChanged(object sender, SelectionChangedEventArgs e)
{
var previous = e.PreviousSelection;
var current = e.CurrentSelection;
...
}
I improved Fabricio P. answer in this way:
Used {RelativeSource Self} for SelectionChangedCommandParameter. It helps to omit named collection views.
So your xaml part will be something like this:
<CollectionView
ItemsSource="{Binding Objects}"
SelectionMode="Single"
SelectionChangedCommand="{Binding SelectObjectCommand}"
SelectionChangedCommandParameter="{Binding SelectedItem, Source={RelativeSource Self}}">
And in your view model:
public ICommand SelectObjectCommand => new Command<string>(i => { Debug.WriteLine("Selected: " + i); });
public IEnumerable<string> Objects { get; set; }
It doesn't look like you set the SelectionMode property. According to the docs:
By default, CollectionView selection is disabled. However, this behavior can be changed by setting the SelectionMode property value to one of the SelectionMode enumeration members:
None – indicates that items cannot be selected. This is the default value.
Single – indicates that a single item can be selected, with the selected item being highlighted.
Multiple – indicates that multiple items can be selected, with the selected items being highlighted.
Adding SelectionMode = Single to the CollectionView will resolve your problem.
if you are using the Model for it you can use the following method
My C# Model View Class
public class MainView : INotifyPropertyChanged
{
public ICommand SelectionChangedCommands => new Command<GroupableItemsView>((GroupableItemsView query) =>
{
GO_Account test = query.SelectedItem as GO_Account;
});
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
And this is my XAML
<CollectionView x:Name="myAccounts"
SelectionMode="Single"
ItemsSource="{Binding Products}"
SelectionChangedCommand="{Binding SelectionChangedCommands}"
SelectionChangedCommandParameter="{Binding Source={x:Reference myAccountsModel}}">
</CollectionView>
Creating a Registration page, I need to get the following data from user.
First Name
Last Name
Username
Email
Password
Date of Birth
Gender
User Role
For the last two parameters, I am unable to find how to use radio buttons in Xamarin.Forms. Following is my code for the Registration Page.
<StackLayout BackgroundColor="#30af91" Padding="60">
<Entry Text="{Binding FirstName}" Placeholder="First Name"/>
<Entry Text="{Binding LastName}" Placeholder="Last Name"/>
<Entry Text="{Binding UserName}" Placeholder="Last Name"/>
<Entry Text="{Binding Email}" Placeholder="Email" />
<Entry Text="{Binding Password}" Placeholder="Password" IsPassword="True"/>
<Entry Text="{Binding ConfirmPassword}" Placeholder="Confirm Password" IsPassword="True"/>
<DatePicker MinimumDate="1/1/1948" MaximumDate="12/31/2007"/>
<!--Radio buttons for Gender
1. Male 2.Female-->
<!--Radio Buttons for UserRole
1. Admin 2.Participant-->
<Button Command="{Binding RegisterCommand}" Text="Register"/>
<Label Text="{Binding Message}" />
</StackLayout>
Xamarin forms does not provide Radio Button.
You can either use
1)Switch
2)Picker
or any other component to fulfill your requirement
UPDATE
The xamarin forms update version 4.6 has introduced the Radio button control, Here is the official documentation
I think there is a simpler solution that is fairly easy and requires no libraries. Really a a radio group is just a fancy ListView. You would just need to create a viewModel for each radio button that has a IsSelected flag and switch between 2 images. I had a need to allow a user to select how long a token persisted:
XAML
<ListView
HasUnevenRows="True"
HorizontalOptions="FillAndExpand"
ItemsSource="{Binding Durations}"
ItemSelected="ListView_ItemSelected"
SelectedItem="{Binding SelectedDuration}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout
Orientation="Horizontal">
<Image
HeightRequest="18"
IsVisible="{Binding IsSelected}"
Source="radioButtonChecked.png"
WidthRequest="18"/>
<Image
HeightRequest="18"
IsVisible="{Binding IsUnselected}"
Source="radioButtonUnchecked.png"
WidthRequest="18"/>
<Label
Margin="8,0,0,0"
Text="{Binding Caption}"/>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
We create a listview in our content page and listen for the ItemSelected event. Each list item is a horizontal stack panel where we flip between two images depending on the selected state
Code Behind
public partial class LoginPage : ContentPage
{
LoginPageViewModel LoginPageViewModel { get; }
public LoginTwoFactorFrequencyPage ()
{
BindingContext = LoginPageViewModel = new LoginPageViewModel();
InitializeComponent ();
}
private void ListView_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
LoginPageViewModel.UpdateSelected(e.SelectedItem as PersistenceDuration);
}
}
The page's code behind instantiates a view model and calls an UpdateSelected method with the newly selected item on the page's view model*
RadioButton ViewModel
The view model for each radio button:
public class PersistenceDuration : ViewModelBase
{
bool isSelected;
public string Caption { get; set; }
public TwoFactorTokenPersistenceDuration Duration { get; set; }
public bool IsSelected
{
get => isSelected;
set
{
isSelected = value;
OnPropertyChanged();
OnPropertyChanged("IsUnselected");
}
}
public bool IsUnselected => !IsSelected;
public PersistenceDuration(string caption, TwoFactorTokenPersistenceDuration duration)
{
Caption = caption;
Duration = duration;
IsSelected = false;
}
}
The radio button view model holds selection info and the caption. We make sure to fire OnPropertyChanged whenever the selected state changes
Page ViewModel
public class LoginPageViewModel : ViewModelBase
{
PersistenceDuration duration;
PersistenceDuration selectedDuration;
public ObservableCollection<PersistenceDuration> Durations { get; }
public PersistenceDuration SelectedDuration
{
get => selectedDuration;
set
{
if (value != null)
{
duration = value;
UpdateSelected(duration);
}
OnPropertyChanged();
}
}
public LoginTwoFactorFrequencyViewModel()
{
Durations = new ObservableCollection<PersistenceDuration>(
new List<PersistenceDuration>()
{
new PersistenceDuration(AppResources.Save_code__forever, TwoFactorTokenPersistenceDuration.Forever),
new PersistenceDuration(AppResources.ChatRequireEvery30Days, TwoFactorTokenPersistenceDuration.ThirtyDays),
new PersistenceDuration(AppResources.ChatRequireEveryLogin, TwoFactorTokenPersistenceDuration.None),
});
}
public void UpdateSelected(PersistenceDuration persistenceDuration)
{
foreach (var item in Durations)
item.IsSelected = persistenceDuration == item;
}
}
In the page view model we create a list of radio button view models that the XAML binds to. When we UpdateSelected() all the IsSelected states are updated which trigger binding updates which flip the image.
You will still need to do something about the highlight when someone selects an item, but that is easy enough to find on the internet :)
You can use XLabs plugin from manage NuGets package. After installing you can use like this:
In Xaml:
controls:BindableRadioGroup x:Name="Radiobtn"
In C#:
string[] gender = {"MAlE","FEMALE"}
Radiobtn.Add(gender)
Refer Link
https://github.com/XLabs/Xamarin-Forms-Labs/tree/master/samples/XLabs.Samples/XLabs.Samples/Pages/Controls
You can get the radio button effect without a package. Use Labels with text unicode circle \u26AA or \u25CB. Attach a tab gesture recognizer to each label.
When tapped, change the text of the selected button to unicode circle bullet \u29BF and change the text of the other button(s) back to unicode circle \u26AA.
Test on your preferred platforms as each platform may display somewhat differently. You may need to adjust the font size as you change the text.
If you want real radiobuttons you can xlabs their package (https://github.com/XLabs/Xamarin-Forms-Labs/tree/master/src/Forms/XLabs.Forms/Controls/RadioButton)
Personally I'd just use a picker, Xlabs package hasn't been updated in a while so their might be some bugs in the radiobutton
You can use image as a radio button. When tou you click on it, it can change. It is not a good way to do it though.
This is xaml code:
<Image Scale="0.7" HorizontalOptions="Start" x:Name="radioButton" Source="unRadioBtn.png">
<Image.GestureRecognizers>
<TapGestureRecognizer Tapped="radioButton_Clicked"></TapGestureRecognizer>
</Image.GestureRecognizers>
</Image>
And this is .cs:
private void radioButton_Clicked(object sender, EventArgs e)
{
radioButton.Source = "radioBtn.png";
}
Xamarin.Forms 4.6 introduced a new RadioButton control. You can find the documentation here: https://learn.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/radiobutton
You can use the switch component. Also you can see the implementation for a checkbox component from the XLabs project which is now discontinued, get the code and modify it as you need.
Hint: You're gonna need the custom renderers per platform for it to work .
You need to use Picker
https://developer.xamarin.com/api/type/Xamarin.Forms.Picker/
Actually it is the best alternative to RadionButton On Xamarin.forms
XLabs RadioButton and BindableRadioGroup work well: XLabs RadioButton for Xamarin Forms
Here's a simple Yes/No radio using the BindableRadioGroup:
var answers = new List<string>();
answers.Add("Yes");
answers.Add("No");
var RadioGroup = new XLabs.Forms.Controls.BindableRadioGroup()
{
ItemsSource = answers,
Orientation = StackOrientation.Horizontal
};
Xamarin Forms now provides a Radio Button control.
See docs here:
https://learn.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/radiobutton
As of XF 4.8 this is still experimental and I've not yet used this feature so can't comment on its stability.
I have a Listview in Xaml and I need to bind ItemTapped event to my ModelView using MVVM.
My ListView looks like.
<ListView x:Name="list"
ItemsSource="{Binding employeeList}"
ItemTapped= {Binding selectedItem} >
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<ViewCell.View>
</ViewCell.View>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
ItemTapped is an event which, in MVVM, normally corresponds to an ICommand*. If you meant to bind to a normal data property, judging from the attempted binding statement in your XAML snippet, then it would make more sense to do bind ListView's SelectedItem property instead :
<ListView x:Name="list"
ItemsSource="{Binding EmployeeList}"
SelectedItem="{Binding SelectedItem}">
.....
</ListView>
If there is data related action that need to be taken upon ItemTapped event occur, it might instead be implemented on SelectedItem property changed which triggered via binding (as in the XAML binding above) :
private ItemModel _selectedItem;
public ItemModel SelectedItem
{
get { return _selectedItem; }
set
{
if(_selectedItem != value)
{
_selectedItem = value;
OnPropertyChanged();
//this can be placed before or after propertychanged notification raised,
//depending on the situation
DoSomeDataOperation();
}
}
}
*) Xamarin Blog : Turn Events into Commands with Behaviors
I'm using MVVM in this project, I have a listbox which bind to a collection of Customers. I want to create an event to navigate a detailsPage using id of the elementselected:
<ListBox ItemsSource="{Binding Customers}" x:Name="state_list" SelectionChanged="state_list_SelectionChanged">
<i:Interaction.Triggers>
<i:EventTrigger EventName="selectionchanged">
<cmd:EventToCommand Command="{Binding stateSelectedCommand}" PassEventArgsToCommand="True" />
</i:EventTrigger>
</i:Interaction.Triggers>
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Vertical">
<TextBlock Text="{Binding nom}" />
<!--TextBlock Text="{Binding LastName}" />
<TextBlock Text="{Binding Text, ElementName=tbCount}" /-->
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I can't figure out how to get the selected item to add it to the uri and then use it to get data. An example or tutorial would be helpful. Thanks :)
I would create a "SelectedCustomer" property in the ViewModel (next to you Customers property) and bind it to the SelectedItem. Then, on the setter of that property you can navigate to your desired page. This way you eliminate the messy events and command.
<ListBox x:Name="state_list
ItemsSource="{Binding Customers}"
SelectedItem="{Binding SelectedCustomer, Mode=TwoWay}">
...
public Customer SelectedCustomer
{
get
{
return _selectedCustomer;
}
set
{
if (value != null)
{
_selectedCustomer = value;
//Navigate to your page here, either with Navigator class or any other mechanism you have in place for changing content on screen
}
}
}
AlexDrenea gives you a good way of binding SelectedItem to a property on your viewmodel. If you are wanting to navigate based on this in an MVVM architecture, I would suggest using messaging to get it done.
I cover this in a blog post I did a while back, but the short summary of doing this within MVVMLight, is to create a Navigator class that sits at the application level.
public class Navigator
{
private PhoneApplicatoinFrame RootFrame;
public Navigator(PhoneApplicationFrame frame)
{
RootFrame = frame;
RegisterMessages();
}
private void RegisterMessages()
{
Messenger.Default.Register<ShowTrackerMessage>(this, ShowTracker);
}
private void ShowTracker(ShowTrackerMessage msg)
{
RootFrame.Navigate(new Uri("/Views/ItemLocationCompassView.xaml", UriKind.RelativeOrAbsolute));
}
}
Then, as part of your application start-up, create it and pass it a reference to your RootFrame:
private static Navigator _navigator;
public static Navigator Nav
{
get { return _navigator; }
}
...
_navigator = new Navigator(this.RootFrame);
Then, you have a couple choices on how you send the Navigation message.
Option 1: In your ViewModel, hook into the PropertyChanged event (part of INotifyPropertyChanged), and send the appropriate message when your SelectedItem property changes.
Option 2: Tie into the SelectionChanged event of your ListBox. I use the MVVMLight's EventToCommand to send that event to a RelayCommand in my ViewModel, then react appropriately to send the message to the Navigator object.
I cover this in more detail at: http://www.smartchitecture.com/?p=27
This question already has an answer here:
Closed 11 years ago.
Possible Duplicate:
Binding between Usercontrol with listbox and parent control (MVVM)
I’m trying to bind a UserControl to property on my main page’s viewmodel
The code looks like this:
UserControl xaml:
<UserControl x:Class="myUserControl" ....>
<Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}" >
<ListBox Name="myListBox" ItemsSource="{Binding Path=myItemsSource}"/>
</Grid>
</UserControl>
the codebehind looks like this:
public partial class myUserControl : UserControl
{
public static DependencyProperty ItemsSourceProperty =
DependencyProperty.Register("myItemsSource",
typeof(IEnumerable), typeof(myUserControl), null);
public IEnumerable myItemsSource
{
get
{
return (IEnumerable)GetValue(ItemsSourceProperty);
}
set
{
SetValue(ItemsSourceProperty, value);
}
}
}
The UC is used like this in the main page:
<phone:PhoneApplicationPage DataContext="{Binding myViewModel, Source={StaticResource Locator}}" ....>
<Grid x:Name="ContentPanel">
<uc:myUserControl x:Name="ucList" myItemsSource="{Binding Path=DataList}"/>
</Grid>
</phone:PhoneApplicationPage>
and the viewModel for the main page look like this:
public class myViewModel : ViewModelBase
{
public ObservableCollection<myObject> DataList
{
get
{
return _datalist;
}
set
{
if (_dataList != value)
{
_dataList = value;
RaisePropertyChanged("DataList");
}
}
}
}
But when the DataList property is set, the uc List in not populated.
What i'm I missing ?
It's still early and I haven't had my coffee yet, but it looks to me like you might need a data template for your list items. You've defined the ItemsSource but not told the control how to render the items themselves.
What does your list contain? Try binding a data template to one of the list item properites, like this:
<UserControl x:Class="myUsercontrol" ....>
<Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}" >
<ListBox Name="myListBox" ItemsSource="{Binding Path=myItemsSource}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding SomeListItemProperty}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>
EDIT: Are you by chance using MVVM Light? I saw that you mentioned {StaticResource = Locator} in one of the comments. That would be helpful to know.
One other thing you might try is checking if your UserControl is in its own namespace. If you put it in a UserControl folder, it might be. I've had some issues with binding a UserControl when it wasn't in the same namespace as the ViewModel.