Why does a Bound Textbox not modify its associated property is the Text value is set programmatically?

Question

I have a Windows Form with a number of Textboxes. I bind them to a DataSource as the Form Loads.

public partial class FormSettings : Form
{
    private readonly DbContext _context = new DbContext();

    public FormSettings()
    {
        InitializeComponent();
    }

    protected override void OnLoad(EventArgs e)
    {
        _context.OrderEntrySettings.Load();

        SettingsBindingSource.DataSource = _context.OrderEntrySettings.Local.ToBindingList();

        Binding saNbinding = new Binding("Text", SettingsBindingSource, "InvoiceNumber");

        InvoiceNumberTextBox.DataBindings.Add(saNbinding);

        Binding pthNbinding = new Binding("Text", SettingsBindingSource, "SalesOrderExportPath");

        PathTextBox.DataBindings.Add(pthNbinding);

    <snip>
    …   
    </snip>
}

One of the Textboxes is bound to a Directory Path (string) Property. If I type in a new directory in the Path Textbox and hit my save button, The path saves just fine.

But, If I change the Text Property on the Textbox to the SelectedPath from a FolderBrowserDialog dialog and then hit save, the Textbox Text shows the directory I selected but the Entity is not modified and nothing gets saved back to the database.

As a workaround, I set both the Path Textbox Text and set the Property from the context to the SelectedPath.

Why does a Bound Textbox not modify its associated property if the Text value is set programmatically?

Answer 1

这是原因。结合类有一个叫做财产DataSourceUpdateMode有3个选择- Never，OnPropertyChanged并且OnValidation，在最后的是一个默认值。以Text编程方式设置属性时，没有验证/验证事件，因为它们仅在控件处于焦点并已被编辑时才触发，因此绑定不会更新数据源。

话虽这么说，以下是您可以选择的选项：

（A）不要以编程方式设置控件属性，而是设置数据源属性。

（B）将绑定更改DataSourceUpdateMode为OnPropertyChanged。但是，这将导致在用户键入的每个字符上更新数据源属性。

（C）使用以下代码段：

yourTextBox.Text = ...;
yourTextBox.DataBindings["Text"].WriteValue();