如何在WPF中添加，保存和加载项目到列表视图

Question

About two weeks ago I started to develop in WPF and, since I only developed in WinForms, I ran into common problems but managed to find the solution for them. However, currently I'm stuck at something: adding items with multiple columns (via visual basic code, not xaml) into a listview.

I'm not sure if it's best to use a Listview or a DataGrid control for this but basically I want the user to be able to add favourite songs to a list, save them to a file and load the file whenever the app is opened. The listview currently has three columns: Artist, Song and Status.

When I was programming in WinForms, I used to do this:

        Dim Song As New ListViewItem
        Form1.ListView1.Items.Add(Song)
        Song.Text = TextBox1.Text
        Song.SubItems.Add(TextBox2.Text)
        Song.SubItems.Add(TextBox3.Text)

Then, to save:

   Dim Song As New ListViewItem
            Form1.ListView1.Items.Add(Song)
            Song.Text = TextBox1.Text
            Song.SubItems.Add(TextBox2.Text)
            Song.SubItems.Add(TextBox3.Text)
            Try
                Dim myWriter As New IO.StreamWriter(PATH_DATABASE)
                For Each myItem As ListViewItem In Form1.ListView1.Items
                    myWriter.WriteLine(myItem.Text & "|" & myItem.SubItems(1).Text & "|" & myItem.SubItems(2).Text & "|" & myItem.SubItems(3).Text
                Next
                myWriter.Close()
            Catch ex As Exception
                MsgBox("Error: " & ex.Message, vbCritical, "Error")
            End Try

I've been searching and I've found that I need to use binding so I've tried this:

Imports System
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
Imports System.Windows


Public Structure Song

    Public _artist As String
    Public _title As String
    Public _status As String

    Property Artist() As String
        Get
            Return _artist
        End Get
        Set(ByVal Value As String)
            _artist = Value
        End Set
    End Property
    Property Title() As String
        Get
            Return _title
        End Get
        Set(ByVal Value As String)
            _title = Value
        End Set
    End Property
    Property Status() As String
        Get
            Return _status
        End Get
        Set(ByVal Value As String)
            _status = Value
        End Set
    End Property
End Structure



Public Class WINDOW_AddSong

    Dim songs As New ObservableCollection(Of Song)




    Private Sub Button1_Click(sender As Object, e As RoutedEventArgs) Handles Button1.Click
        Dim Song As New ListViewItem

        For Each wnd As Window In Application.Current.Windows
            If wnd.GetType Is GetType(MainWindow) Then

                DirectCast(wnd, MainWindow).Listview1.Items.Add(Alimento)
                Alimento.Content = New Song() With {._artist = "Lol", ._title = "Lol2", ._status = "Lol3"}




            End If
        Next
    End Sub
End Class

And in the XAML listview:

<GridViewColumn Header="Artist" DisplayMemberBinding="{Binding Artist}"/>
<GridViewColumn Header="Title" DisplayMemberBinding="{Binding Title}"/>
<GridViewColumn Header="Status" DisplayMemberBinding="{Binding Status}"/>

This works however I'm not sure if this is the WPF-way of doing things.

However, I'm stuck at the saving process:

 Try
            Dim myWriter As New IO.StreamWriter(PATH_DATABASE)
            For Each wnd As Window In Application.Current.Windows
                If wnd.GetType Is GetType(MainWindow) Then
                    For Each myItem As ListViewItem In DirectCast(wnd, MainWindow).Listview1.Items
                        myWriter.WriteLine(Song, Artist, Status)
                    Next
                End If
            Next
            myWriter.Close()
        Catch ex As Exception
            MsgBox("Error: " & ex.Message, vbCritical, "Error")
        End Try

This doesn't work. Also, PATH_DATABASE is just a directory.

To summarise, could an expert review my code and check if I'm doing things "right" and, if possible, could you help me with the saving and loading process?

Thanks.

Answer 1

I just updated your structure (I used a class, just force of habit) to use automatic property values which are available in recent versions of VS. The default implementation of properties is built in along with the backer fields. It is used just as before.

You are on the right track with ObservableCollection but you you need to implement INotifyPropertyChanged by adding the Event PropertyChanged and providing the Sub OnPropertyChanged to raise the event.

Set up the bindings on the controls and set the ItemsSource ot the ListView to your ObservableList.

To save Import System.Text so you can use a StringBuilder. The loop through the list to build the string to save to a text file.

I didn't spend any time trying to make the XAML Windows look nice. Pardon the ugliness.

Class MainWindow
    Public Songs As New ObservableCollection(Of Song)

    Protected Sub OnLoad(sender As Object, e As RoutedEventArgs)
        Songs.Add(New Song("Nirvana", "Smells Like Teen Spirit", "Open"))
        Songs.Add(New Song("John Lennon", "Imagine", "In Stock"))
        Songs.Add(New Song("U2", "One", "Unknown"))
        Songs.Add(New Song("Michael Jackson", "Billie Jean", "Open"))
        lvSongs.ItemsSource = Songs
    End Sub

    Private Sub BtnAdd_Click(sender As Object, e As RoutedEventArgs)
        Dim frm As New frmAdd
        frm.mainForm = Me 'send the instance of the current form to the new form
        frm.ShowDialog()
    End Sub

    Private Sub SaveList()
        Dim sb As New StringBuilder
        For Each item As Song In Songs
            sb.AppendLine($"{item.Artist}|{item.Title}|{item.Status}")
        Next
        'call sb.ToString and write it to a .txt file
    End Sub
End Class

MainWindow XAML

<Window x:Class="MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WPF_BindComboBox"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid Loaded="OnLoad"
          Name="root">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>

        </Grid.RowDefinitions>
        <ListView Margin="10" Name="lvSongs" Grid.Row="0">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <WrapPanel>
                        <TextBlock Text="Name: " />
                        <TextBox x:Name="txtArtist" 
                                 Text="{Binding Artist, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
                                 FontWeight="Bold"/>
                        <TextBlock Text=", " />
                        <TextBlock Text="Age: " />
                        <TextBox Text="{Binding Title}" 
                                 FontWeight="Bold" />
                        <TextBlock Text=" (" />
                        <TextBox Text="{Binding Status}"  />
                        <TextBlock Text=")" />
                    </WrapPanel>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
        <Button x:Name="btnAdd" Grid.Row="1" Height="25" Width="100" Content="Add a Song" Click="BtnAdd_Click"/>      
    </Grid>
</Window>

The Song class

Public Class Song
    Implements INotifyPropertyChanged

    Public Property Artist() As String
    Public Property Title() As String
    Public Property Status() As String

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Protected Sub OnPropertyChanged(ByVal name As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name))
    End Sub

    Public Sub New(art As String, Ttl As String, Stat As String)
        Artist = art
        Title = Ttl
        Status = Stat
    End Sub
End Class

The Add Window

Public Class frmAdd

    Public mainForm As MainWindow

    Private Sub BtnAdd_Click(sender As Object, e As RoutedEventArgs)
        mainForm.Songs.Add(New Song(txtArtist.Text, txtTitle.Text, txtStatus.Text))
        ClearForm()
    End Sub

    Private Sub ClearForm()
        txtArtist.Clear()
        txtTitle.Clear()
        txtStatus.Clear()
    End Sub

End Class

Add Window XAML

<Window x:Class="frmAdd"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WPF_BindComboBox"
        mc:Ignorable="d"
        Title="frmAdd" Height="172.641" Width="307.547">
    <Grid >
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="100"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <TextBlock Grid.Column="0" Grid.Row="0" Text="Artist" FontSize="16" FontWeight="Bold"/>
        <TextBox x:Name="txtArtist" Grid.Column="1" Grid.Row="0" FontSize="16" Width="150" />
        <TextBlock Grid.Column="0" Grid.Row="1" Text="Title" FontSize="16" FontWeight="Bold"/>
        <TextBox x:Name="txtTitle" Grid.Column="1" Grid.Row="1" FontSize="16" Width="150"/>
        <TextBlock Grid.Column="0" Grid.Row="2" Text="Status" FontSize="16" FontWeight="Bold"/>
        <TextBox x:Name="txtStatus" Grid.Column="1" Grid.Row="2" FontSize="16" Width="150"/>
        <Button x:Name="btnAdd" Grid.Column="1" Grid.Row="4" Content="Add Song" Click="BtnAdd_Click"/>
    </Grid>
</Window>

EDIT Required Imports

Imports System.Collections.ObjectModel
Imports System.ComponentModel
Imports System.Text