5. Windows Forms Datagrid

5.1 How can I programatically set the rowheight of a row in my DataGrid?

You can do this by starting a new thread and executing Application.Run for the status dialog form when the background thread starts running. To communicate changes in percentage use BeginInvoke to executes a specific delegate asynchronously on the thread that the form was created on.

Download the ProgressThread progressthread.zip sample for a complete implementation of a BackgroundThreadStatusDialog class that shows a status dialog in a separate thread.

In order to use BackgroundThreadStatusDialog from your code you have to update the Progress inside your loop and check the IsCanceled state to detect if the user pressed the Cancel button.

5.2 How can I autosize the rowheights in my datagrid?

Here is a solution suggested by Matthew Benedict. It uses reflection to access the protected DataGridRows collection so he can set the row height.

5.3 How do I prevent sorting a single column in my DataGrid?

You can implement the IMessageFilter interface in your main form. This amounts to adding an override for PreFilterMessage, and looking for the particular message you need to catch. Here are code snippets that catch an escape key on a keydown. You can download a sample project(C#, VB). In the sample, there are two forms, with several controls. You'll notice that no matter what form or control has input focus, the escape key is caught in the PreFilterMessage override.

5.4 How do I programmatically select a row in DataGrid?

We have a small sample that shows how to do this. Download PropTab.zip. After you download and unzip the sample, build the project. Both the control assembly and a small driver assembly get built. After that add the control to your toolbox using 'Customise toolbox...'. Then drag and drop an instance of the added control onto the form in the driver winforms sub-project. When you select this control the properties window should have a tab with a bitmap 'T' as shown below.

These are the steps involved. Before following these steps please download and take a look at the sample. That will greatly help when following these steps.

Control related steps

Assume that you have a control that has two sets of properties, one set that you wish to have displayed in the main property tab and another set that you wish to have displayed in the second tab.

• Mark those properties that you wish to display in the first tab with the BrowsableAttribute to true.
• Mark those properties that you wish to display in the second tab with the BrowsableAttribute set to false. Create another attribute. Name it anything you want and give it a single boolean property. Initialize this property to true.

Other steps

• Derive a class from System.Windows.Forms.PropertyGridInternal.PropertiesTab. You have to override a few methods. The most important of these is GetProperties. We override GetProperties as shown below to use our CustomAttribute as the filtering attribute instead of the BrowsableAttribute that the PropertyGrid uses by default.

5.5 How can I translate a point to a cell in the datagrid?

PE refers to portable executable. The file format used for executable programs and for files to be linked together to form executable programs. It includes both metadata information that describes types and members referenced in your program, and the MSIL that is the code base for the program. Source: .NET Framework SDK Documentation

5.6 I lost the settings in my DataGrid set during design-time?

This is possible if you assign a custom DataGridTableStyle to the DataGrid. The properties in the DataGridTableStyle will then replace certain properties in the DataGrid. Take a look at DataGrid class reference for a list of these properties.

5.7 How do I prevent a click into the grid highlighting a cell?

Here is a technique for binding an arraylist of objects where the objects contain public property that can appear as columns in the datagrid. In this example, the object contains 2 public doubles, one named value and the other named sqrt. To bind this arraylist to a datagrid, add a custom tablestyle that has a MappingName of "ArrayList", and then use the property names as the MappingName for each column. Below are some code snippets. You can download a working project that also has code to delete rows and add new rows to the bound arraylist.

5.8 How do I prevent the datagrid from displaying its append row (the row at the end with an asterisk)?

The DataGrid class does not have a property that controls whether a new row can be added. But the DataView class does have such a property (along with some others such as AllowEdit and AllowDelete). Here is code that will turn off the append row by getting at the dataview associated with the datagrid.

If your datagrid contains links, then Matthew Miller suggest adding Navigate handler such as the one below to disallow the AddNew.

5.9 How can I catch a double-click into a column header cell?

You can use the DataGrid's double-click event and its HitTest method to catch a double click on a header.

5.10 How can I select the entire row when the user clicks on a cell in the row?

Call the DataGrid.Select method from within its mouseup event.

5.11 How can I get text from a column header in a MouseUp event?

5.12 How do I hide a column?

There are several ways to hide a column:

1) You can use your DataSet's ColumnMapping property to hide a column.

2) Another way to hide a column is to set its width to zero. Check out the FAQ How do I set the width of a column in my DataGrid?.

3) Another way to hide a column is to create a custom table style, and as you add columnstyles to your tablestyle, omit the column you want hidden. Check out the FAQ How do I add an unbound column in my bound DataGrid? to see how to create a custom table style.

5.13 How do I color a individual cell depending upon its value or some external method?

We give three different methods for doing this.

Method 2
To use some method to provide the cell color, you can use a similar technique as discussed above. But instead of setting the color based on cell value, call a delegate method instead. This delegate can be passed in using the constructor for the custom column style. You can download a sample that shows how this can be done.

Method 3
If you want a more flexible solution, you could expose an event as part of your derived columnstyle that fires in the Paint override. This would allow the handler of the event to set the color value depending upon the row and column parameters that are passed as part of the event args. You can download a sample (C#, VB) that implements this technique. The sample actually handles allowing a cell to be editable on a cell by cell basis through an event. This sample colors the back ground of the disabled cell gray. You could modify the eventargs to include a backcolor, and use this event to color cells based on row and column values removing the event call in the Edit override.

5.14 How can I put a checkbox in a column of my DataGrid?

You create a custom DataTableStyle that contains column styles for each column you want to display. You add the column styles in the order you want them to appear. Here are the steps to add an string column, an int column and a bool check column to a DataGrid. You can also download a working project.

5.15 How can I restrict the keystrokes that will be accepted in a column of my datagrid?

You can create a custom column style and handle the KeyPress event of its TextBox member. Below is the code showing how this might be done. You can also download a sample project (C#, VB) that shows an implementation of this idea.

5.16 How do I make a field auto increment as new rows are added to my datagrid?

5.17 How can I prevent a particular cell from being editable?

You can do this by deriving a custom column style and overriding its virtual Edit member. Below is an override that will prevent the cell in row 1 of the column from getting the edit focus. You can paste this code in the DataGridDigitsTextBoxColumn sample to see it work.

If you want a more flexible solution, you could expose an event as part of your derived columnstyle that fires right before the call to the baseclass in the Edit override. This would allow the handler of the event to set the enable value depending upon the row and column parameters that are passed as part of the event args. You can download a sample (C#, VB) that implements this technique. The sample also fires the event right before painting the cell to decide whether to paint a gray background for the disabled cell. You could modify the eventargs to include a backcolor, and use this event to color cells based on row and column values.

5.18 How do I move columns in a datagrid?

The columns appear in the order that their column styles were added to the tablestyle being used by the grid. If you want to change this order, you would need to create a new table style, and add the columnstyles in the order you want things to appear. Here is some code snippets that suggest how to do this.

5.19 How can I do cell by cell validation in a datagrid?

There are problems trying to implement cell by cell validation using the grid's Validating event architecture. The problem is that the grid is not the object handling the data. Instead, a TextBox or some other control is the control managing the changing of the cell contents. One way to implement the validation at the grid level is to handle the CurrentCellChanged event, and if the previous cell's value is not proper, then return to that cell. You can download a sample that implements this process. The sample only handles the validation from cell to cell movement. If you want to handle the validation when the user clicks on the forms Close button, then you would have to add a special event handler for this and do one last validation at this point.

5.20 How do I programmatically determine the selected rows in a datagrid?

The method DataGrid.IsSelected can tell you if a particular row is selected. So, you could use IsSelected in a loop through all your rows to finds if multiple rows have been selected. Depending upon the size of your datagrid, this may be a viable solution. If not, you could track the selections yourself by monitoring the key actions and the mouse actions. This would be more work. Thanks to John Hughes to the suggestion to use the dataview.

5.21 How can I bind the datagrid to a datasource without using any wizards?

Here is a really simple data binding sample. Just drag and drop a datagrid onto a default Windows Forms application. Follow the steps below to bind this grid to the NorthWind db in SQL server.

5.22 How can I bind two datagrids in a Master-Detail relationship?

Please download this sample before reading the rest of this FAQ. Looking through the sample will help follow the description.

What this boils down to is this:
1) Load both Master and Details queries in a dataset.

2) Bind the master data grid to the Master dataset table.

3) Create a relationship that describes how the two tables relate to each other. A primary key foreign key relationship is defined by two attributes.
The primary key column in the master table
The foreign key column in the details table
The created relationship is added to the dataset.

4) Set the data member for the details table to be the name of relationship that was added to the dataset.

5.23 How do I get the row or column that has been clicked on?

You can use the DataGrid's HitTest method, passing it a point in the grid's client coordinate system, and returning a HitTestInfo object that holds all the row and column information that you want.

5.24 How do I add an unbound column to my bound datagrid?

The idea is to create the 'bound' table in your dataset, and then add an extra 'unbound' column. The steps are to derive a custom columnstyle that overrides Paint where you calculate and draw the unbound value. You can also override Edit to prevent the user from selecting your unbound column. Then to get your datagrid to use this special column style, you create a tablestyle and add the column styles to it in the order you want the columns to appear in the datagrid. Here are code snippets that derive the column and use the derived column. You can download a working sample.

5.25 How do I get the row and column of the current cell in my datagrid?

You can use the CurrentCell property of the DataGrid.

5.26 How can I prevent the Enter key from moving to the next cell when the user is actively editing the cell and presses Enter?

Override the method ProcessKeyPreview in your DataGrid.

5.27 How do I set the width of a column in my DataGrid?

To set a column width, your datagrid must be using a non-null DataGridTableStyle. Once this is in place, you can set the column width by first getting the tablestyle and then using that object to obtain a column style with which you can set the width. Here are some code snippets showing how you might do this.

5.28 How can I implement OLE Drag & Drop between a DataGrid and another OLE DnD object that supports the Text format?

The attached samples (C#, VB) have a derived datagrid that supports OLE D&D with any OLE D&D provider that handles a Text formatted data object. The derived grid handles six events to allow it to be both a drop source and a drop target. The sample project has two datagrids where you can drag cell text back and forth. You can also open Excel, and drag text between Excel and either datagrid.

Here are the events that are handled in this sample.

5.29 How can I tell if the current row has changed and whether I am on the AddNew row or not?

The DataGrid's CurrentCellChanged event is hit even if you just change cells in the current row. If you want an event that is only hit when you change rows, then you have to look at the binding manager. This object has both a CurrentChanged event and a PositionChanged event which are hit when you change rows.

To decide whether you are on the AddNew row or not, you can again use the binding manager and compare the number of rows it returns with the number of rows in your data table. Below is some code snippets showing how you might get at this information.

5.30 How do I hide the gridlines or set them to a particular color?

If your datagrid does not have a custom TableStyle associated with it, then there are two DataGrid properties that control the color and visibility of the gridlines.

If you have a custom TableStyle. you need to set the color within the TableStyle. Here is code that makes the line color the same as the background color, and hence hides the gridlines. You can download a sample.

5.31 How can I get the selected text in an active gridcell?

You need to get the DataGridTextBoxColumn.TextBox member, and retrieve the SelectedText from it for the active cell. The sample shows how you can do this as part of handling this TextBox's rightClick. This code assumes you have specifically added DataGridTextBoxColumn for each column style. You can also download a VB sample.

5.32 How do I determine whether a checkbox in my datagrid is checked or not?

If the column is a boolean column, you can just cast the object returned by the indexer to a bool and use it.

5.33 How can I move rows by dragging the row header cell?

One way to implement this is to derive a DataGrid and override the virtual OnMouseDown, OnMouseMove and OnMouseUp methods. In your overrides, if the mousedown is on a row header, track the initial mousedown row, and as it moves, draw a line to indicate a target position. Then on the mouseup, handle moving the row.

You can download a sample (C#, VB) that illustrates how this might be done.

5.34 How can I control the cursor over my DataGrid?

One way you can do this is to derive the DataGrid and override its WndProc method to handle the WM_SETCURSOR method yourself. In your override, you can do hit testing to decide when you want to set the cursor, or when you want to call the base class and let it set the cursor. Here are sample projects (VB and C#) showing the technique.

5.35 After scrolling with the mouse wheel on a selected row in a DataGrid I cannot get it back into view. Is there a work around?

When you select a row in the DataGrid and scroll it out of view using the mouse wheel, you cannot get it back into view. The following is a workaround posted by one Windows Forms User:

5.36 How can I make the DataGrid column be blank and not display (null) as the default value?

When you go to a new row in a DataGrid, the columns display (null). To prevent this behavior and make all the columns be empty, you can set the DefaultValue property of the DataColumn to be String.Empty.

5.37 How can I add a DateTimePicker column style to the DataGrid?

This MSDN reference shows how how to create DateTimePicker column style in the DataGrid.

5.38 How can I put a combobox in a column of a datagrid?

The CollectionEditor allows adding and removing items from a collection at design time. If the items in this collection implement IComponent or if they are derived from Component, the items in your collection can be persisted in code.

Download collectioneditorsample.zip for a complete sample project.

2) Next implement your Collection. You have to implement the Ilist interface. The CollectionEditor will determine the type of instances to be added to your collection using reflection inspecting the return type of the Item property (Indexer).

3) Reference this collection in your control or component that should be designable. You need to supply a DesignerSerializationVisibility and an Editor attribute:

5.39 I want to do custom handling of special keys such as the Tab key or F2 in the TextBox of a column in the DataGrid. How do I subclass this TextBox to get at it virtual members?

You have to access a property called the Binding Context and then retrieve the BindingContext associated with the dataset and data member that you used for binding. After you have access to this object you just set the position property. You can move backward and forward through the dataset.

Remember that when you scroll through the dataset all associated controls will scroll since they all depend on the same context. This is useful if you want to have several controls that display sections of a row operate in tandem.

5.40 How can I have a column of icons in my datagrid?

You need to derive a custom column style, override its Paint method and draw the image. In the attached samples, (VB and C#), there are two custom column styles. One style is a stand-alone unbound column that just displays an image. The second custom column style adds the image to the left side of a bound column. In both cases, the actual image that is displayed is from an imagelist passed into the column in its constructor. The index of the image to be drawn on a particular row is determined by a delegate passed into the column style through its constructor.

5.41 How can I make my DataGrid support a single select mode, and not the default multiselect mode?

One way to do this is to derive a DataGrid, override its OnMouseDown and OnMouseMove methods. In the OnMouseDown, handle selecting and unselecting in your code without calling the base class if the click is on the header. In the OnMouseMove, don't call the baseclass to avoid dragging selections. Below is a code snippet for a sample derived DataGrid. You can download a full project (C#, VB).