I use the following ViewModel in my test project. I've tried to follow MVVM pattern. I need instant update feature in the view.

public class StudentListViewModel : INotifyPropertyChanged
    {
        private string _name;
        private string _lastName;
        private int _age;
        private ObservableCollection<Student> _studentList;
        public string Name 
        {
            get => _name;
            set
            {
                _name = value;
                OnPropertyChanged("Name");
                InsertCommand.RaiseCanExecuteChanged();
            }
        }
        public string LastName
        { 
            get => _lastName;
            set
            {
                _lastName = value;
                OnPropertyChanged("LastName");
                InsertCommand.RaiseCanExecuteChanged();
            }
        }
        public int Age
        {
            get => _age;
            set
            {
                _age = value;
                OnPropertyChanged("Age");
                InsertCommand.RaiseCanExecuteChanged();
            }
        }
        public RelayCommand InsertCommand { get; }

        public StudentListViewModel()
        {
            InsertCommand = new RelayCommand((s) => InsertStudent(),
            () => !string.IsNullOrEmpty(Name) && !string.IsNullOrEmpty(LastName) && Age > 0);
            using (MyContext context = new MyContext())
            {
                studentList = new ObservableCollection<Student>(context.Students);
            };
        }
        public void InsertStudent()
        {
                Student st = new Student()
                {
                    Name = Name,
                    LastName = LastName,
                    Age = Age
                };
            using (var context = new MyContext())
            {
                context.Add(st);
                context.SaveChanges();
            }
        }
        public ObservableCollection<Student> studentList
        {
            get 
            {
                return _studentList;
            }
            set
            {
                _studentList = value;
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }

The problem is that when I add an entry to the database, it does not update the ListView and the change is only seen when I rerun the app. The second problem is that property is changed when I leave the cursor focus away from the selected textbox. Is it possible to change property as you fill the property?

CodePudding user response：

there is not need to reload entire collection as shown in the other answer. add single item into the current collection:

public void InsertStudent()
{
    var st = new Student()
    {
        Name = Name,
        LastName = LastName,
        Age = Age
    };
    using (var context = new MyContext())
    {
        context.Add(st);
        context.SaveChanges();
    }
    studentList.Add(st);
}

CodePudding user response：

You are missing OnPropertyChanged in studentList:

public ObservableCollection<Student> studentList
        {
            get 
            {
                return _studentList;
            }
            set
            {
                _studentList = value;
                OnPropertyChanged(“studentList”);
            }
        }

EDIT:

You need to load the list again when insert a data:

public void InsertStudent()
        {
                Student st = new Student()
                {
                    Name = Name,
                    LastName = LastName,
                    Age = Age
                };
            using (var context = new MyContext())
            {
                context.Add(st);
                context.SaveChanges();
                studentList = new ObservableCollection<Student>(context.Students);
            }
        }