Should ViewModels inherit other ViewModels?
I have a MerchandiserViewModel that contains the basic properties and database functions for a Merchandiser model.
The MerchandiserViewModel has a SelectedMerchandiser property that holds the selected Merchandiser from the ItemSelected in a ListView
MerchandiserViewModel.cs
public MerchandiserViewModel : INotifyPropertyChanged
{
// Property to hold the selected Merchandiser
// Generally I would make this static but then I can't bind the property
public Merchandiser SelectedMerchandiser {get; set;}
// Other logic...
}
The MerchandiserViewModel is instantiated as a Static Resource in App.xaml so that I only have one instance of the view model.
App.xaml
<?xml version="1.0" encoding="utf-8" ?>
<Application xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MobileApp.App"
xmlns:ViewModels="clr-namespace:MobileApp.ViewModels">
<Application.Resources>
<ViewModels:MerchandiserViewModel x:Key="MerchandiserViewModel" />
<ViewModels:MerchandiserProfileViewModel x:Key="MerchandiserProfileViewModel" />
</Application.Resources>
</Application>
For each View related to a Merchandiser e.g. MerchandiserProfile, EditProfile etc. I create a new ViewModel and inherit the MerchandiserViewModel
MerchandiserProfileViewModel.cs inherits the MerchandiserViewModel
public class MerchandiserProfileViewModel : MerchandiserViewModel
{
// Logic Specific to the Merchandiser Profile View
}
The problem is... when I create a new [Page]ViewModel and inherit the "MerchandiserViewModel" I receive the following error message.
I think this may be because a new instance of the MerchandiserViewModel is created so I am not referencing the initial SelectedMerchandiser property.
This makes me think that inheriting ViewModels isn't a good idea?
How is this situation usually handled? Should I just jam all logic for each page/view into the one MerchandiserViewModel? I want my code to be as clean an separated as possible, so would like to avoid this if possible.
AFTER THOUGHT
Am I able to access the properties of the MerchandiserViewModel in static Resource in C#? this way I could pass the required properties to the new ViewModel without inheriting the MerchandiserViewModel ... keen to hear thoughts on this?
The MerchandiserViewModel has a SelectedMerchandiser property that holds the selected Merchandiser from the ItemSelected in a ListView
According to your description, you want to binding for ListView, for MerchandiserViewModel, you don't need to inherit other ViewModels, I suggest you can take a look the Model-View-ViewModel Pattern
I do one sample that binding ListView using MVVM, please take a look.
<StackLayout>
<ListView
x:Name="listview1"
HasUnevenRows="True"
ItemsSource="{Binding mers}"
SelectedItem="{Binding selecteditem}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout>
<Label
FontSize="Large"
Text="{Binding Name}"
VerticalOptions="Center" />
<Label
FontSize="Small"
Text="{Binding PhoneNumber}"
VerticalOptions="Center" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
The model class,contains some properties that binding to UI.
public class Merchandiser
{
public string Name { get; set; }
public string PhoneNumber { get; set; }
}
The MerchandiserViewmodel class, the view model implements properties and commands to which the view can data bind to, and notifies the view of any state changes through change notification events. The properties and commands that the view model provides define the functionality to be offered by the UI, but the view determines how that functionality is to be displayed.
public class MerchandiserViewmodel:ViewModelBase
{
public ObservableCollection<Merchandiser> mers { get; set; }
private Merchandiser _selecteditem;
public Merchandiser selecteditem
{
get { return _selecteditem; }
set
{
_selecteditem = value;
RaisePropertyChanged("selecteditem");
}
}
public MerchandiserViewmodel()
{
mers = new ObservableCollection<Merchandiser>();
getdata();
}
private void getdata()
{
for(int i=0;i<20;i++)
{
Merchandiser mer = new Merchandiser();
mer.Name = "merchandiser "+i;
mer.PhoneNumber = "123";
mers.Add(mer);
}
}
}
The ViewModelBase is class that implementinf INotifyPropertyChanged interface, notify data changed. For MerchandiserViewmodel, the Selected Merchandiser(selecteditem) must implement INotifyPropertyChanged to notify data change when you selected item from ListView every time.
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Binding ViewModel to ContentPage
public partial class Page10 : ContentPage
{
public Page10()
{
InitializeComponent();
this.BindingContext = new MerchandiserViewmodel();
}
}
Update:
If you want to navigate to detailed page when select ListView item, you can use constructor pass by value in ListView_ItemSelected event.
<StackLayout>
<ListView
x:Name="listview1" ItemSelected="listview1_ItemSelected" SelectionMode="Single"
HasUnevenRows="True"
ItemsSource="{Binding mers}"
SelectedItem="{Binding selecteditem}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout>
<Label
FontSize="Large"
Text="{Binding Name}"
VerticalOptions="Center" />
<Label
FontSize="Small"
Text="{Binding PhoneNumber}"
VerticalOptions="Center" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
private async void listview1_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
Merchandiser item = (Merchandiser)e.SelectedItem;
await Navigation.PushAsync(new simplecontrol.Page29(item));
}
Detailed Page:
<ContentPage.Content>
<StackLayout>
<StackLayout Orientation="Horizontal">
<Label Text="Name: " />
<Label
FontSize="Large"
Text="{Binding Name}"
VerticalOptions="Center" />
</StackLayout>
<StackLayout Orientation="Horizontal">
<Label Text="PhoneNumber: " />
<Label
FontSize="Small"
Text="{Binding PhoneNumber}"
VerticalOptions="Center" />
</StackLayout>
</StackLayout>
</ContentPage.Content>
public partial class Page29 : ContentPage
{
public Page29(Merchandiser mer)
{
InitializeComponent();
this.BindingContext = mer;
}
}
Related
I want to create an application that can Create, Read, Update and Delete Merchandiser records.
I am struggling with how to "Update" and "Delete" a record based on a ItemSelected in the ListView.
The item selected in the ListView represents a Merchandiser and is currently being passed into each new View as an argument.
I intend to store data in an SQLite database, but for simplicity have not included any of that logic. Database Commands (Save, Delete etc.) will be created in the MerchandiserViewModel
Here is my slimmed down code so far
Merchandiser.cs Model
public class Merchandiser
{
public string Name { get; set; }
public string PhoneNumber { get; set; }
// Additional Properties not shown for simplicity
}
MerchandiserViewModel.cs ViewModel
public class MerchandiserViewModel : ViewModelBase
{
public ObservableCollection<Merchandiser> MerchandiserList { get; set; }
private Merchandiser selectedItem;
public Merchandiser SelectedItem
{
get { return selectedItem; }
set
{
selectedItem = value;
RaisePropertyChanged();
}
}
public MerchandiserViewModel()
{
MerchandiserList = new ObservableCollection<Merchandiser>();
CreateData();
}
private void CreateData()
{
for (int i = 0; i < 20; i++)
{
Merchandiser merchandiser = new Merchandiser();
merchandiser.Name = $"Merchandiser {i}";
merchandiser.PhoneNumber = $"12{i}6{i*3}{i*8}{i*9/3+2}";
MerchandiserList.Add(merchandiser);
}
}
}
// Database commands and other logic not shown...
}
BaseViewModel.cs
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
MerchandiserListPage.xaml & .cs View - Display List of Merchandiers
<?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="MVVM.Views.MerchandisersListPage">
<ContentPage.Content>
<StackLayout>
<ListView x:Name="MerchandiserListView"
ItemSelected="MerchandiserListView_ItemSelected"
SelectionMode="Single"
HasUnevenRows="True"
ItemsSource="{Binding MerchandiserList}"
SelectedItem="{Binding SelectedItem}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout>
<Label
FontSize="Large"
Text="{Binding Name}"
VerticalOptions="Center" />
<Label
FontSize="Small"
Text="{Binding PhoneNumber}"
VerticalOptions="Center" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage.Content>
</ContentPage>
// MerchandisersListPage.xaml.cs - Code Behind
public MerchandisersListPage()
{
InitializeComponent();
this.BindingContext = new MerchandiserViewModel();
}
private async void MerchandiserListView_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
Merchandiser merchandiser = (Merchandiser)e.SelectedItem;
await Navigation.PushAsync(new MerchandisersProfilePage(merchandiser));
}
MerchandisersProfilePage.xaml & .cs
This page should navigate to the MerchandiserEditPage using an Edit Button but I'm not sure if I am handling the 'Code Behind' correctly?
<?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="MVVM.Views.MerchandisersProfilePage">
<ContentPage.Content>
<StackLayout>
<StackLayout Orientation="Horizontal">
<Label Text="Name: " />
<Label
FontSize="Large"
Text="{Binding Name}"
VerticalOptions="Center" />
</StackLayout>
<StackLayout Orientation="Horizontal">
<Label Text="PhoneNumber: " />
<Label
FontSize="Small"
Text="{Binding PhoneNumber}"
VerticalOptions="Center" />
</StackLayout>
<Button Text="Edit"
Clicked="EditButton_Clicked"/>
</StackLayout>
</ContentPage.Content>
</ContentPage>
// MerchandisersProfilePage.xaml.cs - Code Behind
Merchandiser selectedMerchandiser;
public MerchandisersProfilePage(Merchandiser merchandiser)
{
InitializeComponent();
selectedMerchandiser = merchandiser; // Is this what I should be doing?
this.BindingContext = merchandiser;
}
private async void EditButton_Clicked(object sender, EventArgs e)
{
// Am I doing this the correct way??
await Navigation.PushAsync(new MerchandiserEditPage(selectedMerchandiser));
}
MerchandiserEditPage.xaml & .cs This is where I am stuck.
I will need to update the record in the database by calling a method in the MerchandiserViewModel but am not sure how to do this? The method (which ideally should be called by a Command) to update the database has the following signature UpdateMerchandiser(Merchandiser merchandiser).
Ideally I would like the Save Button to use a Command instead of Clicked so I can access the Save command in the MerchandiserViewModel but this imposes another problem around form validation. How then can I then validate this information (e.g. Name is not empty) before saving it the the database? Because the MerchandiserViewModel doesn't know anything about the MerchandiserEditPage.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"
x:Class="MVVM.Views.MerchandiserEditPage">
<ContentPage.Content>
<StackLayout>
<StackLayout Orientation="Horizontal">
<Label Text="Name: " />
<Entry
FontSize="Large"
Text="{Binding Name}"
VerticalOptions="Center" />
</StackLayout>
<StackLayout Orientation="Horizontal">
<Label Text="PhoneNumber: " />
<Entry
FontSize="Small"
Text="{Binding PhoneNumber}"
VerticalOptions="Center" />
</StackLayout>
<!-- Ideally this should use 'Command' instead of 'Clicked' -->
<Button Text="Save"
Clicked="SaveButton_Clicked"/>
</StackLayout>
</ContentPage.Content>
</ContentPage>
// MerchandiserEditPage.xaml.cs - Code Behind
public MerchandiserEditPage(Merchandiser merchandiser)
{
InitializeComponent();
this.BindingContext = merchandiser;
}
// I would prefer not to use an event handler but use a Command in the MerchandiserViewModel instead
// I also need to perform some basic validation e.g. Name entry should not be empty etc.
private async void SaveButton_Clicked(object sender, EventArgs e)
{
// How can I Save/Update the changes?
// Pop() page off the stack and return to the MerchandiserProfileView
await Navigation.PopAsync();
}
I believe the above code is designed in accordance to MVVM, however if not, please advise where I am violating this pattern?
I also want to do similar for deleting a record but once I get the update method sorted I'm sure deleting will follow similar logic.
Note: The code above is not shown in its entirety and is missing SQLite database functionality and other logic for simplicity. All functionality to the database (Save, Update, Delete) is in the MerchandiserViewModel. I will edit or add any additional information to this question as required to help provide a complete picture of the problem.
I have a problem. I created this class that creates an ImageSource collection ObservableCollection<TemplateSource>:
public class TemplateListViewModel
{
public ObservableCollection<TemplateSource> sourceList { get; set; }
public TemplateListViewModel()
{
sourceList = new ObservableCollection<TemplateSource>();
loadingTemplates += onLoadingTemplates;
LoadTemplateList();
}
private event EventHandler loadingTemplates = delegate { };
private void LoadTemplateList()
{
loadingTemplates(this, EventArgs.Empty);
}
private async void onLoadingTemplates(object sender, EventArgs args)
{
List<Template> templateList = await App.RestService.GetTemplates(App.User);
foreach (var template in templateList)
{
ImageSource source = ImageSource.FromUri(new Uri("mysite.org/myapp/" + template.FileName));
TemplateSource templateSource = new TemplateSource { Id = template.Id, Source = source };
sourceList.Add(templateSource);
}
}
}
And in my XAML I use this code:
<ContentPage.Content>
<StackLayout HorizontalOptions="Fill">
<Frame IsClippedToBounds="True" HeightRequest="45" CornerRadius="5" Padding="0" Margin="15,15,15,0" BackgroundColor="Transparent">
<Entry Placeholder="Search" ReturnType="Done" PlaceholderColor="Gray" x:Name="txtSearch" Margin="5,0,0,0" TextColor="White" />
</Frame>
<CollectionView ItemsLayout="HorizontalList" ItemsSource="{Binding sourceList}">
<CollectionView.ItemTemplate>
<DataTemplate>
<ff:CachedImage
Source="{Binding .}"
VerticalOptions="Center"
HorizontalOptions="Fill" />
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</StackLayout>
</ContentPage.Content>
And finally in the page.xaml.cs (code behind):
protected override void OnAppearing()
{
TemplateListViewModel vm = new TemplateListViewModel();
BindingContext = vm;
base.OnAppearing();
}
Now I already got help with this code from #Deczaloth, but he couldn't figure out why the CollectionView stays emtpy after I bind it. Now I already checked, but the sourceList does get filled, so thats not the problem.
What am I doing wrong?
I can see one potential problem in your code XD:
When you bind the Source property of CachedImage you set the binding to ".", but you should instead bind to the Source property of the TemplateSource class (in your context "." means a TemplateSource item!), that is you should change your code like so:
<ff:CachedImage
Source="{Binding Source}"
VerticalOptions="Center"
HorizontalOptions="Fill" />
In my Xamarin.Forms app I have a simple Contact class [Model]. In the UI [View] there exists a ListView that displays the Contacts. In my model view class I have a list of Contacts (_listOfContacts) that is assigned to the itemSource property of the ListView. This list of Contacts is an ObservableCollection. My issue is the when user clicks Delete from ContextActions I can see that the _listOfContacts is updated but the ListView is not.
The ListView is only updated when I reassign its itemsource to the _listOfContacts. This should not be needed if _listOfContacts is an ObservableCollection of Contacts.
I am new to MVVM so I need to clear these basic MVVM concepts before I go on to learn more advanced techniques.
Here is my code:
Model
class Contact
{
public String Name { get; set; }
public String Status { get; set; }
public String ImageUrl { get; set; }
}
Model View
public partial class ContactListPage : ContentPage
{
private ObservableCollection<Contact> _listOfContacts;
public ContactListPage()
{
InitializeComponent();
_listOfContacts = new ObservableCollection<Contact>
{
new Contact {Name="Item1", ImageUrl="http://lorempixel.com/100/100/people/1" , Status="Hey"},
new Contact { Name = "Item2", ImageUrl = "http://lorempixel.com/100/100/people/2", Status="Hey" },
};
contactList.ItemsSource = _listOfContacts.ToList();
}
private void EditContactClick(object sender, EventArgs e)
{
DisplayAlert("Alert", "Clicked Edit", "Cancel");
}
private void DeleteContactClick(object sender, EventArgs e)
{
var contact = (sender as MenuItem).CommandParameter as Contact;
_listOfContacts.Remove(contact);
//following line of code should not be needed since _listOfContacts is
//an ObservableCollection and removing an item should update the bound control automatically
**contactList.ItemsSource = _listOfContacts.ToList();**
}
}
View
<ContentPage.Content>
<StackLayout>
<ListView x:Name="contactList" HasUnevenRows="True">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal" Padding="10">
<Image Source="{Binding ImageUrl}"/>
<StackLayout HorizontalOptions="StartAndExpand">
<Label Text="{Binding Name}" Margin="0,2,0,2"/>
<Label Text="{Binding Status}" Margin="0,2,0,2" />
</StackLayout>
</StackLayout>
<ViewCell.ContextActions>
<MenuItem Text="Edit" Clicked="EditContactClick" CommandParameter="{Binding .}"/>
<MenuItem Text="Delete" Clicked="DeleteContactClick" IsDestructive="True" CommandParameter="{Binding .}"/>
</ViewCell.ContextActions>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage.Content>
I have tested your code, it is just the method ToList()which caused this question:
contactList.ItemsSource = _listOfContacts.ToList();
At the beginning, the type of _listOfContacts is ObservableCollection, but when you use the method ToList(),then it will been converted to List again.
So just delete the method 'ToList()', your code will work properly, just as follows:
contactList.ItemsSource = _listOfContacts;
Remove .toList() from contactList.ItemsSource = _listOfContacts.ToList(); and try again.
_listOfContacts is an ObservableCollection which should be used as your ItemsSource directly. Maybe go and check out the ObservableCollection documentation.
I'm very new to Xamarin.Forms and MVVM and posting questions here on StackOverflow so bear with me please. I'm trying to fill a listview in Xamarin.Forms. I first programmed it without MVVM and it all worked like I wanted it to, but now I wanted to get in in MVVM and that is where it went wrong, now my list won't fill up anymore.
I made a viewmodel and only put all the binding in the viewmodel, I have not yet implemented eventhandlers.
This is a part of the code behind (I have a couple more eventhandlers but that is not relevant right now):
namespace CCXamarinApp
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class PatientsWithTagPage : ContentPage
{
public PatientsWithTagPage()
{
BindingContext = new PatientsWithTagViewModel();
InitializeComponent();
(BindingContext as PatientsWithTagViewModel).GetAllPatients();
if((BindingContext as PatientsWithTagViewModel).IsEmptyPatientList)
HandleEmptyList();
else
(BindingContext as PatientsWithTagViewModel).SortAndShowPatients();
}
private void SearchBar_OnTextChanged(object sender, TextChangedEventArgs e)
{
(BindingContext as PatientsWithTagViewModel).Searching(e.NewTextValue);
}
...
This is my XAML page:
<SearchBar x:Name="SearchBar" Placeholder="Zoek op naam of plaats..." HeightRequest="25" Margin="10"
TextChanged="SearchBar_OnTextChanged"/>
<Label Text="{Binding LastRefreshed}" FontAttributes="Italic" FontSize="15" />
<Label x:Name="LabelEmptyList" FontSize="17" Text="Geen gegevens gevonden" FontAttributes="Bold"
IsVisible="False" />
<ListView x:Name="PatientListView" HasUnevenRows="True" SeparatorColor="Accent"
VerticalOptions="FillAndExpand" IsPullToRefreshEnabled="True" IsRefreshing="{Binding IsFetchingData, Mode=TwoWay}"
Refreshing="PatientListView_OnRefreshing" SelectedItem="{Binding SelectedPatient, Mode=TwoWay}"
ItemSelected="PatientListView_OnItemSelected" ItemsSource="{Binding Patients}"
IsVisible="True" BackgroundColor="Aqua">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Spacing="4">
<StackLayout Orientation="Horizontal" Margin="10,7,10,1">
<Label Text="{Binding FullName}" FontAttributes="Bold" FontSize="16" />
<Label Text="{Binding DisplayTimeOfLastScan, StringFormat='{0}'}"
HorizontalOptions="EndAndExpand" />
</StackLayout>
<StackLayout Orientation="Horizontal" Margin="10,0,10,7">
<Label Text="{Binding LastLocation}" HorizontalOptions="Start" />
<Label Text="{Binding DisplayDurationSinceLastScan, StringFormat='al {0}'}"
HorizontalOptions="EndAndExpand" />
</StackLayout>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage.Content>
This is my viewmodel (not all the code but the code that is most relevant). The BaseViewModel it derives from is from the nuget package "Refractored.Mvvmhelpers":
class PatientsWithTagViewModel : BaseViewModel
{
public ObservableCollection<PatientViewModel> Patients { get; private set; } = new ObservableCollection<PatientViewModel>();
private PatientViewModel selectedPatient;
public PatientViewModel SelectedPatient
{
get => selectedPatient;
set => SetProperty(ref selectedPatient, value);
}
private readonly JsonSerializerSettings jsonSerializerSettings = new JsonSerializerSettings
{
DateFormatString = "dd-MM-yyyTH:mm",
DateTimeZoneHandling = DateTimeZoneHandling.Utc,
};
public bool IsEmptyPatientList => Patients.Count == 0;
private string testJson = "[{\"firstName\":\"P.\",\"lastName\":\"Selie\",\"tag\":{\"tagId\":\"124\",\"tagSerialNumber\":\"ABC135\"},\"scans\":[{\"location\":\"Tuin\",\"dateTime\":\"May01,2018,10:10\"},{\"location\":\"Eetzaal\",\"dateTime\":\"May02,2018,10:15\"},{\"location\":\"Gang\",\"dateTime\":\"May02,2018,11:10\"},{\"location\":\"Kamer23\",\"dateTime\":\"May02,2018,12:09\"}],\"id\":\"dcc4fe9929b3681f\"}," +
"{\"firstName\":\"W.\",\"lastName\":\"Janssens\",\"tag\":{\"tagId\":\"132\",\"tagSerialNumber\":\"ABC167\"},\"scans\":[{\"location\":\"Kamer23\",\"dateTime\":\"May01,2018,23:39\"},{\"location\":\"Gang\",\"dateTime\":\"May02,2018,04:10\"},{\"location\":\"Eetzaal\",\"dateTime\":\"May02,2018,04:11\"},{\"location\":\"Gang\",\"dateTime\":\"May02,2018,04:20\"},{\"location\":\"Kamer23\",\"dateTime\":\"May02,2018,04:22\"}],\"id\":\"a6dac28475327922\"}]";
public void GetAllPatients()
{
IsFetchingData = true;
try
{
Patients = new ObservableCollection<PatientViewModel>(
JsonConvert.DeserializeObject<ObservableCollection<PatientViewModel>>(testJson,
jsonSerializerSettings));
}
catch(Exception e)
{
Console.WriteLine("*****ERROR kon API niet ophalen");
Console.WriteLine(e.Message);
}
finally
{
IsFetchingData = false;
}
}
This is the model I use:
public class Patient : ObservableObject
{
public string FirstName { get; set; }
public string LastName { get; set; }
public Tag Tag { get; set; }
public List<Scan> Scans { get; set; }
public string Id { get; set; }
public override string ToString()
{
return LastName + ", " + FirstName;
}
}
It also has its own viewmodel with properties like DisplayDurationSinceLastScan, but I don't think it is relevant here, if you think it is, let me know.
So with this code I get my page but there seems to be no items in the list, if I debug, Patients is filled with items so it is not empty at all, but something goes wrong with the binding I guess but no error is given.
Here is a picture of what I get: the listview is shown (I added a blue background so I would know if the listview was visible or not), but there are no items in there. Still Patients is filled when I debug the app.
Does someone see the mistake I made?
I see some issues with your code here from a maintainability point of view. Try to keep all your code inside the view model instead of both the view model and code behind. Ideally, your code behind contains nothing and if anything it strictly has to do with visual things.
Anyway, in regard to you problem: you are creating a new ObservableCollection each time. That breaks the binding. Just keep the new ObservableCollection at the top and then when new data comes in, clear that and repopulate it. Like this:
public void GetAllPatients()
{
IsFetchingData = true;
try
{
var resultPatients = JsonConvert.DeserializeObject<ObservableCollection<PatientViewModel>>(testJson, jsonSerializerSettings);
Patients.Clear();
foreach (var patient in resultPatients)
Patients.Add(patient);
}
catch(Exception e)
{
Console.WriteLine("*****ERROR kon API niet ophalen");
Console.WriteLine(e.Message);
}
finally
{
IsFetchingData = false;
}
}
Your data should now show up.
I have built a List<> of item objects, which are being used as the ItemsSource to a ListView. on my ListView's ItemSelected event, I am trying to change one of the elements of that particular item. The original values are bound from the object.
Please consider the following example:
itemClass.cs
class itemClass
{
public itemClass()
{
}
public string valueIWantToChange {get; set;}
}
MyPage.cs
public MyPage()
{
InitializeComponent();
List<itemClass> listOfItems= new List<itemClass>();
itemClass item1= new itemClass { valueIWantToChange = "UnClicked"};
listOfItems.Add(item1);
BindingContext = this;
lstView.ItemsSource = listOfItems;
lstView.ItemSelected += (sender, e) =>
{
if (e.SelectedItem == null)
{
return;
}
// The below does nothing but highlights what I am trying to achieve
((itemClass)((ListView)sender).SelectedItem).valueIWantToChange = "Clicked" ;
((ListView)sender).SelectedItem = null;
};
}
My 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:myProject="clr-namespace:myProject"
x:Class="myProject.MyPage">
<StackLayout>
<ListView x:Name="lstView">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Padding="0" Orientation="Vertical" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
<Label Text="{Binding valueIWantToChange }" TextColor="Black" FontSize="16" VerticalOptions="Center" HorizontalOptions="Center" Margin="5,5,5,5"/>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage>
I have attempted to use Binding commands and PropertyChangedEventHandler but with no success. Any assistance in this would be greatly appreciated.
Edit
I have attempted to use PropertyChangedEventHandlers in a similar way, elsewhere in the app, please see below:
public double FontXLarge
{
set
{
someFontsize = value;
OnPropertyChanged("FontXLarge");
}
get
{
someFontsize = scalableFont(10);
return someFontsize;
}
}
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
The above allows me to bind a fontsize to that scaling font, however if I were to use something similar for string, would it not effect all of the items in the ListView?
I think the best way to implement what you want, it's to use a ViewModel with INotifyPropertyChanged. You can find a lot of example if you're googling a bit. One good link for generic baseclass is this.
Let me know if you find everything you need.