datasource Updating when bind to user property

Question

C#, VS-2010, winforms

Generally I want to create user control with a bindable MyProperty. But I met some problem: Data row become modified when current row changed.

You can download C# project and try it yourself: test_bind.zip

To make it simple I did follow:

create test form with a
- dataGridView (set it ReadOnly),
- TextBox,
- some typed DataSet with some Table
- bindingSource
bind bindingSource to the table
bind dgv to bindingSource
bind TextBox.Text to bindingSource to some text column ("name")
on form load fill table with some data. (If you add rows manually do not forget AcceptChanges())
add event handler for table xxx_ColumnChanging(...) and set breakpoint there

all standard steps, nothing special

Run

as expected - rows in dgv, current name in textBox, click on different rows in grid... and only when I modify text in textbox I stop in breakpoint.

Lets modify program, and bind textBox to different property instead of Text - lets say Tag. Set DataSourceUpdateProperty "OnValidation" or "OnPropertyChanged".

Run

Now current row become modified. !!!

Same happens when instead of textBox I use UserControl with a dummy property

String MyProperty { set; get; }

How to bind custom property in user control with the same behaviour as TextBox.Text?

Note: Binding property itself is not a problem. Problem is: when I bind to standard TextBox.Text property - everything Ok Wen I bind to ANY OTHER property (Tag) or to custom Property in User Control - then DATASOURCE ALWAYS BECOME MODIFIED FOR CURRENT ROW

Are you asking how to bind a property on your UserControl - which under the covers binds to a TextBox on that UserControl? — John Arlen
Binding property itself is not a problem. Problem is: when I bind to standard TextBox.Text property - everything Ok Wen I bind to ANY OTHER property (Tag) or to custom Property in User Control - then DATASOURCE ALWAYS BECOME MODIFIED FOR CURRENT ROW — parfilko

parfilko parfilko · Accepted Answer · 2012-09-11T17:13:35

Short answer is:

When bind to simple property, declared like

[Bindable(true, BindingDirection.TwoWay)]           //  I need TwoWay    
public String MyProp {set;get;}

then datasource will be updated on current position change. You may count it as Bug or Feature...

To change behavior - I need magic word. Declare event in the control as

 public event System.ComponentModel.PropertyChangedEventHandler MyPropChanged;

This name is special: "YourPropertyName" + "Changed" = YourPropertyNameChanged Other word will not be magic. As soon as event declared - datasource would not be updated every time as before...

and now I can control the process...

public void OnMyPropChanged(System.ComponentModel.PropertyChangedEventArgs e)
{
    Binding bb = this.DataBindings[0] as Binding;
    bb.WriteValue();
    if (MyPropChanged != null) MyPropChanged(this, e);
}

private void TxtChanged(object sender, EventArgs e)
{
    if (load) { return; }
    _my_prop = Txt.Text;   // ...
    OnValueTwoChanged(new PropertyChangedEventArgs("MyProp"));
}

Here is the example project with more details, where I create user control with String property ValueTwo which split in two different TextBoxes using some custom logic, and combine value and update when user change the text.

test_bind_fixed.zip

And this is article which help me http://support.microsoft.com/kb/327413

datasource Updating when bind to user property

1 Answers