錯誤：使用的ItemsSource

Question

我的XAML文件之前，項集合必須爲空

<ListBox Height="522" HorizontalAlignment="Left" Margin="20,162,0,0" Name="listBox1" VerticalAlignment="Top" Width="448" ItemsSource="{Binding}"> 
    <ListBox.ItemTemplate> 
     <DataTemplate> 
      <StackPanel Orientation="Horizontal"> 
       <TextBlock Text="{Binding Text}" Foreground="#FFC8AB14" FontSize="36" /> 
      </StackPanel> 
     </DataTemplate> 
    </ListBox.ItemTemplate> 
</ListBox> 

xaml.cs文件

 listBox1.Items.Clear(); 
     for (int i = 0; i < tasks.Count(); i++) { 
      List<Taskonlistbox> dataSource = new List<Taskonlistbox>(); 
      dataSource.Add(new Taskonlistbox() {Text = "Blalalalala"}); 
      this.listBox1.ItemsSource = dataSource; // visual stdio shows error here: 
     } 

Taskonlistbox：

public class Taskonlistbox 
{ 
    public string Text { get; set; } 
} 

錯誤：「Items集合必須爲空之前使用ItemsSource「 最新問題？

Answer 1

您只想創建一次該列表，並只分配一次數據源！因此，之前創建列表循環並指定數據源後循環

// Clear the listbox. 
// If you never add items with listBox1.Items.Add(item); you can drop this statement. 
listBox1.Items.Clear(); 

// Create the list once. 
List<Taskonlistbox> dataSource = new List<Taskonlistbox>(); 

// Loop through the tasks and add items to the list. 
for (int i = 0; i < tasks.Count(); i++) { 
    dataSource.Add(new Taskonlistbox {Text = "Blalalalala"}); 
} 

// Assign the list to the `ItemsSouce` of the listbox once. 
this.listBox1.ItemsSource = dataSource;