ListBox.SelectedIndexChanged第一次不触发 [英] ListBox.SelectedIndexChanged not firing on first occasion

问题描述

我有一个绑定到BindingList的ListBox，该列表默认情况下为空.
当所选择的指数的变化，它应该与所选择的对象的数据来更新其他控件.点击 问题在于，SelectedIndexChanged事件没有在第一个条目上触发(索引从-1变为0).
但是，当我再次单击第一个条目时(尽管在这种情况下索引不会更改)并添加更多条目时，它确实会触发.
我检查了属性myListBox.SelectedIndex，它实际上从-1更改为0，但由于某种原因未调用事件处理程序. 有谁知道它为什么这样做以及如何解决它?

I have a ListBox bound to a BindingList which is empty by default.
When the selected index changes it's supposed to update other controls with data from the selected object.
The problem is that the SelectedIndexChanged event is not firing on the first entry (index changing from -1 to 0).
It does fire however when I'm clicking on the first entry again (although index is not changing in this case) and when adding any more entries.
I checked the property myListBox.SelectedIndex and it does in fact change from -1 to 0 but for some reason doesn't call the event handler. Does anyone know why it's doing this and how to fix it?

这是我的代码:

public partial class main : Form
{
    // The class of objects in my BindingList
    [Serializable]
    public class DisplayDefinition : INotifyPropertyChanged
    {
        private string _name;
        private int _width, _height, _posx, _posy;

        public string Name { get { return _name; } set { _name = value; NotifyPropertyChanged("Name"); } }
        public int Width { get { return _width; } set { _width = value; NotifyPropertyChanged("Width"); } }
        public int Height { get { return _height; } set { _height = value; NotifyPropertyChanged("Height"); } }

        public event PropertyChangedEventHandler PropertyChanged;
        private void NotifyPropertyChanged(string s)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(s));
        }
    }

    // Defining the BindingList 
    BindingList<DisplayDefinition> displaydefinitions = new BindingList<DisplayDefinition>();

    // Binding the list to my listbox 
    public main()
    {
        InitializeComponent();
        listDisplays.DataSource = displaydefinitions;
        listDisplays.DisplayMember = "Name";
    }

    // Button adding a new object to the list
    private void btnNewDisplay_Click(object sender, EventArgs e)
    {
        DisplayDefinition d = new DisplayDefinition();
        displaydefinitions.Add(d);
        listDisplays.SelectedItem = d;
    }

    private void listDisplays_SelectedIndexChanged(object sender, EventArgs e)
    {
        DisplayDefinition d = (DisplayDefinition)listDisplays.SelectedItem;
        // Do something with "d" ...
    }
}

推荐答案

问题:

仅当将ListBox与数据源一起使用时才会发生此行为，而在手动填充ListBox时不会发生.

The problem:

This behavior only occurs when using the ListBox with a data source, and doesn't occur when filling the ListBox manually.

将第一项添加到数据源时，默认情况下会选择第一项，而不会触发SelectedIndexChanged事件(不确定原因！)，这似乎是一个错误ListBox ，这使得设置SelectedItem或SelectedIndex属性无效.

When adding the first item to the data source, the first item gets selected by default without firing the SelectedIndexChanged event (not sure why!) which seems to be a bug in ListBox, and that makes setting the SelectedItem or SelectedIndex property useless.

您可以在设置实际的SelectedIndex/SelectedItem之前将SelectedIndex属性更改为临时索引(-1)，以触发SelectedIndexChanged事件.

You can change the SelectedIndex property to a temporary index (-1) before setting the actual SelectedIndex/SelectedItem in order to trigger the SelectedIndexChanged event.

类似以下的方法应该起作用:

// Button adding a new object to the list
private void btnNewDisplay_Click(object sender, EventArgs e)
{
    DisplayDefinition d = new DisplayDefinition();
    d.Name = "SomeName";
    displaydefinitions.Add(d);
    listDisplays.SelectedIndex = -1;
    listDisplays.SelectedItem = d;
}

private void listDisplays_SelectedIndexChanged(object sender, EventArgs e)
{
    if (listDisplays.SelectedIndex == -1) return;
    DisplayDefinition d = (DisplayDefinition)listDisplays.SelectedItem;
    // Do something with "d" ...
    Console.WriteLine(d.Name);
}

希望有帮助:)

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