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在DataGrid中使用ComboBox（转贴）

2005-06-01 21:12 525 查看

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Introduction

I needed a

ComboBox

in my

DataGrid

. After looking around on the web, I found many examples, but none of them worked for me.

With inspiration from Alastair Stells article here on The Code Project and what else I found on the Internet, I have made the following

DataGridComboBoxColumn

class.

Why did the other examples not work

All the other examples populate the

ComboBox

with a

DataView

, but I need to (want to be able to) populate my

ComboBox

with an

IList

(

ArrayList

) instead of a

DataView

columnComboBox = new DataGridComboBoxColumn();
columnComboBox.comboBox.DataSource = new ArrayList(MyDataClass.GetArray());
columnComboBox.comboBox.DisplayMember = "Name";
columnComboBox.comboBox.ValueMember = "GUID";

And

MyDataClass.GetArray()

returns

MyDataClass[]

, and has two properties named

Name

and

GUID

.

The other examples expect

columnComboBox.comboBox.DataSource

to be a

DataView

, and it being an

ArrayList

generates exceptions.

I use the ComboBox to fetch display text

Since you don't know the type of

columnComboBox.comboBox.DataSource

, you can't use that to translate between the underlying data and what to display in the

DataGrid

.

Instead, I use the

ComboBox

itself, by overriding the

ComboBox

and implementing this method.

public string GetDisplayText(object value) {
// Get the text.
string text   = string.Empty;
int  memIndex  = -1;
try {
base.BeginUpdate();
memIndex     = base.SelectedIndex;
      base.SelectedValue = value.ToString();
text      = base.SelectedItem.ToString();
base.SelectedIndex = memIndex;
} catch {
} finally {
base.EndUpdate();
}

return text;
} // GetDisplayText

What I do is simple. I select the item which displays the text I want, get the text and then reselects the original item. By doing it this way, it doesn't matter what data source is used.

Because I use the

ComboBox

itself to fetch the display text, the

ComboBox

must be populated before the

DataGrid

is drawn.

Alastair Stells noted about this in his article:

Another issue which arose was an eye-opener! I discovered the
ComboBox
does not get populated until the
ComboBox.Visible
property is set for the first time.

This means that the

ComboBox

can't be used to fetch the initial display text, because it is not visible when the

DataGrid

is first shown (painted).

I use a normal

ComboBox

to illustrate the problem and the solution.

ComboBox comboBox = new ComboBox();
comboBox.DataSource = new ArrayList(MyDataClass.GetArray());
comboBox.DisplayMember = "Name"
comboBox.ValueMember = "GUID"
MessageBox.Show(comboBox.Items.Count.ToString()); // THIS IS ALWAYS 0!

I learned that it didn't help to show the

ComboBox

, but instead I have to set its parent - which internally commits the data from the

DataSource

to the

Items

collection.

ComboBox comboBox = new ComboBox();
comboBox.Parent = this; // this is a Form instance in my case.
comboBox.DataSource = new ArrayList(MyDataClass.GetArray());
comboBox.DisplayMember = "Name"
comboBox.ValueMember = "GUID"
// THIS IS MyDataClass.GetArray().Count
MessageBox.Show(comboBox.Items.Count.ToString());

What else about my DataGridComboBoxColumn

The source code is straight forward. First, I inherited

DataGridTextBoxColumn

, but my class then evolved into inheriting

DataGridColumnStyle

. This meant that I had to implement the

Paint

methods, but at this point, I had some examples of that as well. I like the idea not having an invisible

TextBox

behind it all.

How to use

Sadly, I don't know how to "register" my

DataGridComboBoxColumn

with the

GridColumnStyle

s, enabling me to design the

DataGrid

columns in the designer. This code does it manually.

// Create a DataGridTableStyle object.
DataGridTableStyle  tableStyle   = new DataGridTableStyle();
DataGridTextBoxColumn columnTextBox;
DataGridComboBoxColumn columnComboBox;
tableStyle.RowHeadersVisible     = true;
tableStyle.RowHeaderWidth      = 20;

// Add customized columns.
   columnComboBox       = new DataGridComboBoxColumn();
columnComboBox.comboBox.Parent = this; // Commit dataset.
columnComboBox.comboBox.DataSource = new ArrayList(MyDataClass.GetArray());
columnComboBox.comboBox.DisplayMember = "Name"
columnComboBox.comboBox.ValueMember = "GUID"
columnComboBox.MappingName   = "nameGuid";
columnComboBox.HeaderText   = "Name";
columnComboBox.Width     = 200;
tableStyle.GridColumnStyles.Add(columnComboBox);

columnTextBox       = new DataGridTextBoxColumn();
columnTextBox.MappingName   = "textString";
columnTextBox.HeaderText   = "Text";
columnTextBox.Width     = 200;
tableStyle.GridColumnStyles.Add(columnTextBox);

// Add the custom TableStyle to the DataGrid.
datagrid.TableStyles.Clear();
datagrid.TableStyles.Add(tableStyle);
datagrid.DataSource  = ..... from my database .....;
tableStyle.MappingName  = datagrid.DataSource.GetType().Name;

I think I have focused a problem here: if you want a

ComboBox

in your

DataGrid

, and you want to populate the

ComboBox

from your own custom class and an

ArrayList

.

I hope someone finds it useful - enjoy.

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