>Hi John,
>
>
>About example in the link:
>
https://www.codeproject.com/articles/165368/wpf-mvvm-quick-start-tutorial>
>First case:
>In this case, I’ve :
>One Model: Song, and two ViewModel class:
>public class SongViewModel : ObservableObject and
>class AlbumViewModel , and View
>
>Notice: Model,ViewModel and View there are in link
https://www.codeproject.com/articles/165368/wpf-mvvm-quick-start-tutorial>(example6)
>
>
>
><Window x:Class="Example6.MainWindow"
> xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
> xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
> xmlns:local="clr-namespace:Example6"
> Title="Example 6" Height="464" Width="530" >
> <Window.DataContext>
> <!-- Declaratively create an instance of our Album View Model-->
> <local:AlbumViewModel />
> </Window.DataContext>
> <Grid>
> <Grid.RowDefinitions>
> <RowDefinition Height="Auto" />
> <RowDefinition Height="Auto" />
> <RowDefinition Height="Auto" />
> <RowDefinition Height="Auto" />
> </Grid.RowDefinitions>
> <Grid.ColumnDefinitions>
> <ColumnDefinition Width="Auto" />
> <ColumnDefinition Width="Auto" />
> <ColumnDefinition Width="Auto" />
> <ColumnDefinition Width="Auto" />
> </Grid.ColumnDefinitions>
> <Menu Grid.Row="0" Grid.ColumnSpan="3">
> <MenuItem Header="Test">
> <MenuItem Header="Update Artist" Command="{Binding UpdateAlbumArtists}" />
> <MenuItem Header="Add Artist" Command="{Binding AddAlbumArtist}" />
> <MenuItem Header="Update Songs" Command="{Binding UpdateSongTitles}" />
> </MenuItem>
> </Menu>
>
>>In this case working Update Artist and Update Songs (Button or menu)
>
>
>Second case:
>I’ve one model and one ViewMode and also working Update Artist and Update Songs (Button or menu)
>
>public class Song : ObservableObject
> {
> #region Members
> string _artistName;
> string _songTitle;
> #endregion
>
>
> #region Properties
> public string ArtistName
> {
>
> get { return _artistName; }
> set
> {
> if (_artistName != value)
> {
> _artistName = value;
> RaisePropertyChanged("ArtistName");
> }
> }
> }
>
> public string SongTitle
> {
>
> get { return _songTitle; }
> set
> {
> if (_songTitle != value)
> {
> _songTitle = value;
> RaisePropertyChanged("SongTitle");
> }
> }
> }
>
> #endregion
> }
>
>class AlbumViewModelWithOuthSVM
> {
> #region Members
> private SongDatabase _database = new SongDatabase();
> ObservableCollection<Song> _songs = new ObservableCollection<Song>();
> int _count = 0;
> #endregion
>
> #region Properties
> public ObservableCollection<Song> Songs
> {
> get
> {
> return _songs;
> }
> set
> {
> _songs = value;
> }
> }
>
> private Song _selectedsongs;
> public Song SelectedSongs
> {
> get
> {
> return _selectedsongs;
> }
> set
> {
> if (!Equals((_selectedsongs), value))
> {
> _selectedsongs = value;
> }
> }
> }
>
> #endregion
> #region Construction
> public AlbumViewModelWithOuthSVM()
> {
> for (int i = 0; i < 3; ++i)
> {
> _songs.Add(new Song { ArtistName = _database.GetRandomArtistName, SongTitle = _database.GetRandomSongTitle });
> }
> }
> #endregion
>
> #region Commands
> void UpdateAlbumArtistsExecute()
> {
> if (_songs == null)
> return;
>
> ++_count;
> foreach (var song in _songs)
> {
> song.ArtistName = _database.GetRandomArtistName;
> }
>
> }
>
> bool CanUpdateAlbumArtistsExecute()
> {
> return true;
> }
>
> public ICommand UpdateAlbumArtists { get { return new RelayCommand(UpdateAlbumArtistsExecute, CanUpdateAlbumArtistsExecute); } }
>
>
> void AddAlbumArtistExecute()
> {
> if (_songs == null)
> return;
>
> _songs.Add(new Song { ArtistName = _database.GetRandomArtistName, SongTitle = _database.GetRandomSongTitle });
>
>
> }
>
> bool CanAddAlbumArtistExecute()
> {
> return true;
> }
>
> public ICommand AddAlbumArtist { get { return new RelayCommand(AddAlbumArtistExecute, CanAddAlbumArtistExecute); } }
>
> void UpdateSongTitlesExecute()
> {
> if (_songs == null)
> return;
>
> ++_count;
> foreach (var song in _songs)
> {
> song.SongTitle = _database.GetRandomSongTitle;
> }
> }
>
> bool CanUpdateSongTitlesExecute()
> {
> return true;
> }
>
> public ICommand UpdateSongTitles { get { return new RelayCommand(UpdateSongTitlesExecute, CanUpdateSongTitlesExecute); } }
>
> #endregion
> }
>
><Window x:Class="Example6.MainWindow"
> xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
> xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
> xmlns:local="clr-namespace:Example6"
> Title="Example 6" Height="464" Width="530" >
> <Window.DataContext>
> <!-- Declaratively create an instance of our Album View Model-->
> <local:AlbumViewModelWithOuthSVM />
> </Window.DataContext>
> <Grid>
> <Grid.RowDefinitions>
> <RowDefinition Height="Auto" />
> <RowDefinition Height="Auto" />
> <RowDefinition Height="Auto" />
> <RowDefinition Height="Auto" />
> </Grid.RowDefinitions>
> <Grid.ColumnDefinitions>
> <ColumnDefinition Width="Auto" />
> <ColumnDefinition Width="Auto" />
> <ColumnDefinition Width="Auto" />
> <ColumnDefinition Width="Auto" />
> <ColumnDefinition Width="*" />
> </Grid.ColumnDefinitions>
> <Menu Grid.Row="0" Grid.ColumnSpan="3">
> <MenuItem Header="Test">
> <MenuItem Header="Update Artist" Command="{Binding UpdateAlbumArtists}" />
> <MenuItem Header="Add Artist" Command="{Binding AddAlbumArtist}" />
> <MenuItem Header="Update Songs" Command="{Binding UpdateSongTitles}" />
> </MenuItem>
> </Menu>
> <Label Grid.Column="0" Grid.Row="1" Content="Example 6 - collection" />
>
> <StackPanel Grid.Column=" 0" Grid.Row=" 2">
> <Label Content="{Binding SelectedSongs.ArtistName }"/>
> <Label Content="{Binding SelectedSongs.SongTitle }"/>
> </StackPanel>
>
> <Button Grid.Column="1" Grid.Row="1" Content="Add new artist" Command="{Binding AddAlbumArtist}" />
> <ListView Grid.Column="1" Grid.Row="2" Grid.ColumnSpan="2"
> ItemsSource="{Binding Songs}"
> SelectedItem="{Binding SelectedSongs, Mode=TwoWay}" >
> <ListView.ItemTemplate>
> <DataTemplate>
> <StackPanel>
> <Label Content="{Binding ArtistName}" />
> <Label Content="{Binding SongTitle}" FontSize="10" />
> </StackPanel>
> </DataTemplate>
> </ListView.ItemTemplate>
> </ListView>
> <Button Grid.Column="2" Grid.Row="1" Content="Update Artist Name" Command="{Binding UpdateAlbumArtists}" />
> <Button Grid.Column="3" Grid.Row="1" Content="Update Song Titles" Command="{Binding UpdateSongTitles}" />
> </Grid>
></Window>
>
>>
>
>
>
>My question is:
>
>Why in the second case, if I want to use one model and one VievModel, I have to use the RaisePropertiChanged ("...") in the model, while in the first case I have must to use two ViewMode?
>
>Should not there be in this case one model and one VM, and RaisePropertyChanged("...") to use Only in ViewModel ?
The propertychanged event is the correct mechanism to inform the view model that something has changed. Just focus on that methodology...
