i want to get a parameter with button in xaml

Question

i want to delete or update rows of a list view by the primary key which is Label

Answer

If you want to use a parameter, use the Command and CommandParameter properties, not the Clicked event.

Answer

Hello,

Welcome to our Microsoft Q&A platform!

i want to delete or update rows of a list view by the primary key which is Label.

For testing, I change the Label to Entry. When I click the plus button, the value could be added or updated(if the primary key is not null, PS: I set an ID as primary key). You mentioned that listview in your project. So here is my layout. I wrote two commands for updating and deleting, there are different command ways(Command in listview or outside the listview is different), it depends on you choose.

Here is layout's background code.

   public partial class MainPage : ContentPage  
       {  
           public MainPage()  
           {  
               InitializeComponent();  
               this.BindingContext = new PersonViewModel();  
           }  
       }

Here is my viewModel.

   using System.Collections.ObjectModel;  
   using System.ComponentModel;  
   using System.Linq;  
   using System.Text;  
   using System.Windows.Input;  
   using Xamarin.Forms;  
     
   namespace ListviewUpdate  
   {  
       public class PersonViewModel: INotifyPropertyChanged  
       {  
     
           int _changeID;  
           public int ChangeID  
           {  
               get  
               {  
                   return _changeID;  
               }  
     
               set  
               {  
                   if (_changeID != value)  
                   {  
                       _changeID = value;  
                       OnPropertyChanged("ChangeID");  
     
                   }  
               }  
     
           }  
     
     
           string todo;  
           public string Todo  
           {  
               set  
               {  
                   if (todo != value)  
                   {  
                       todo = value;  
                       OnPropertyChanged("Todo");  
     
                   }  
               }  
               get  
               {  
                   return todo;  
               }  
           }  
     
           public ObservableCollection Persons { get; set; }  
           public ICommand DeleteCommand { protected set; get; }  
           public ICommand UpdateCommand { protected set; get; }  
           public PersonViewModel()  
           {  
               Persons = new ObservableCollection();  
               Persons.Add(new Person() { Name = "Leon1", Image = "favourite.png",Id=1 });  
               Persons.Add(new Person() { Name = "Leon2", Image = "unfavourite.png", Id = 2 });  
               Persons.Add(new Person() { Name = "Leon3", Image = "favourite.png", Id = 3 });  
               Persons.Add(new Person() { Name = "Leon4", Image = "favourite.png", Id = 4 });  
               Persons.Add(new Person() { Name = "Leon5", Image = "unfavourite.png", Id = 5 });  
     
               DeleteCommand = new Command(async (args) => {  
                   Person deletePerson= args as Person;  
                   Persons.Remove(deletePerson);  
               });  
     
     
               UpdateCommand = new Command(async () => {  
                   if (!string.IsNullOrEmpty(Todo))  
                   {  
     
                       Person item = Persons.FirstOrDefault(i => i.Id == ChangeID);  
                       if (item != null)  
                       {  
                           item.Name = Todo;  
                       }  
                       else  
                       {  
                           Persons.Add(new Person() { Id = ChangeID, Name = Todo });  
     
                       }  
                        
                   }  
                    
               });  
     
           }  
     
           public event PropertyChangedEventHandler PropertyChanged;  
     
           protected virtual void OnPropertyChanged(string propertyName)  
           {  
               PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));  
           }  
     
       }

Here is model. I achieved INotifyPropertyChanged for updating property dynamically.

   public class Person : INotifyPropertyChanged  
       {  
     
           int _id ;  
           public int Id  
           {  
               get  
               {  
                   return _id;  
               }  
     
               set  
               {  
                   if (_id != value)  
                   {  
                       _id = value;  
                       OnPropertyChanged("Id");  
     
                   }  
               }  
     
           }  
     
           string name;  
           public string Name  
           {  
               set  
               {  
                   if (name != value)  
                   {  
                       name = value;  
                       OnPropertyChanged("Name");  
     
                   }  
               }  
               get  
               {  
                   return name;  
               }  
           }  
     
            
           string image;  
           public string Image  
           {  
               set  
               {  
                   if (image != value)  
                   {  
                       image = value;  
                       OnPropertyChanged("Image");  
     
                   }  
               }  
               get  
               {  
                   return image;  
               }  
           }  
     
     
           public event PropertyChangedEventHandler PropertyChanged;  
     
           protected virtual void OnPropertyChanged(string propertyName)  
           {  
               PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));  
           }  
     
       }

Here is running screenshot.

Best Regards,

Leon Lu

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Answer

Thank you for your answer ,But i tried it several times and it didn't work ,i'm really confused i did this .

 public class Pins : INotifyPropertyChanged
    {

        [PrimaryKey,MaxLength(250), Unique]
        public string Label { get; set; }

        [MaxLength(250)]
        public string Todo { get; set; }

        [Unique]
        public double Positionlat { get; set; }
        [Unique]
        public double Positionlon { get; set; }
        public ICommand UpdateCommand { protected set; get; }

        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

    }

///////////////////////////////////////////////////////////////////////////////////////////

 public partial class listofinterest : INotifyPropertyChanged
    {
        public List list;
        public ListView lv;
        public ICommand UpdateCommand { protected set; get; }

        public listofinterest()
        {
            InitializeComponent();

            list = App.pinsRepo.GetAllPins();


            listViewEvent.ItemsSource = list;

            UpdateCommand = new Command(async (args) => {
                String Label = args as string;
                _ = Navigation.PushAsync(new AddReminder(Label));
            });

        }


    }

/////////////////////////////////////////////////////////////////////////////

it's not woring and even the INotifyPropertyChanged isn't working when i add something in sqlite it isn't updating property .

i want to get a parameter with button in xaml

3 answers