Introduction
I was looking for an easy and flexible grid filtering mechanism to use with new and old applications. I've found no preexisting solutions that fully satisfy my needs. So, I decided to make my own filtering library. The goals I've tried to reach are:
- Easy to integrate: Availability of a "few lines of code" usage to satisfy the needs of rapid integration.
- User Friendly: Nice to look, easy to use.
- Not code pervasive: Using a
DataGridView derivation would constrain people to re-declare their instances. Moreover, this could be in conflict with existing grid derivations. - Flexible: There are never enough filters in the world!
Using the Code
This is for eager people. The promised "few lines of code" are just one. Add the DgvFilterPopup.dll to your references. Write somewhere a line like this:
DgvFilterManager filterManager = new DgvFilterManager(dataGridView1);
That's all. Your grid is now able to filter the column values. Right-click on the column headers to see a popup with different filtering features, based on the clicked column data type.
Note: Your grid must be data-bound to a DataView, DataTable, or a BindingSource resolving to one of these two.
Class Architecture
The three main classes are exposed in the following diagram:
The DgvFilterManager Class
The DgvFilterManager class doesn't provide a user interface. Its work is to coordinate the interaction between the DataGridView and the visual filtering elements. When you assign a DataGridView to a DgvFilterManager, the latter attaches some handlers to respond to right click on column headers and to perform some custom painting on the grid. When the user right clicks a column header, the DgvFilterManager shows a popup near the column. This popup is a control that serves as a host for other controls, one for each column. Only one of these child controls is visible at a time, based on the clicked column. We have one filter host control and many column filter child controls.
The filter host control must be a derivation of the DgvBaseFilterHost class, while filter controls must be derived from the DgvBaseColumnFilter class. These two classes don't provide any user interface themselves.
As a default, the DgvFilterManager uses a standard host implementation, named DgvFilterHost, and depending on each column type and data type, one of the filter standard implementations (see below): DgvTextBoxColumnFilter, DgvCheckBoxColumnFilter, DgvComboBoxColumnFilter, or DgvDateColumnFilter.
When a DataGridView is attached to the manager, the latter performs the following actions:
- It creates a filter host that is an instance of the
DgvFilterHost class. If you have already provided a filter host, this step is skipped. - It creates a list of
DgvBaseColumnFilters, one per column, and initializes each element to a specialization of DgvBaseColumnFilter. If AutoCreateFilters is false, this step is skipped.
You can force a specific column filter type for a certain column, intervening in this process through the ColumnFilterAdding event. You can also intervene, after the auto-creation process, accessing the filter instances through one of the two indexers provided by the manager, and replacing them with user-chosen instances.
The DgvBaseFilterHost Class
The purpose of the filter host control is to show a popup near a right-clicked column and to host child column filter controls. When the popup is shown, only the column filter control related to the right-clicked column is visible. DgvBaseFilterHost is a derivation of UserControl, and provides functionalities to cooperate with DgvFilterManager.
Note: This class is intended as an abstract class. However, declaring it as abstract would generate errors within the designer when designing derived classes.
In your derivation, you have to provide a host area (such as a panel) and override the FilterClientArea to return it. Also, create visual elements for remove filter, remove all filters, apply filter, and use the DgvFilterManager methods ActivateFilter and ActivateAllFilters to make them alive.
The DgvBaseColumnFilter Class
The purpose of a column filter control is to contain visual elements, allowing the end user to construct a filter. When inheriting from it, you can work just like creating any other user control. This class is a derivation of UserControl, and provides functionalities to cooperate with DgvFilterManager.
Note: This class is intended as an abstract class. However, declaring it as abstract would generate errors within the designer when designing derived classes.
You should override OnFilterExpressionBuilding to provide a filter expression construction logic and to set the values of the FilterExpression and FilterCaption properties.
Standard Implementations
The DgvFilterHost Class
This is the standard implementation of DgvBaseFilterHost. This class does nothing special. Most of the logic is in its base class. It just contains visual elements such as buttons and graphics, and a panel acting as the client area for child column filter controls.
The DgvTextBoxColumnFilter Class
This is one of the DgvBaseColumnFilter standard implementations. It's composed of a combobox containing a list of operators and a textbox in which to type the value of the filter. This column filter is used by default with DataGridViewTextBoxColumns, except when the bound data type is DateTime. The list of available operators is different between string types and numeric types.
The DgvTextBoxColumnFilter Class
A standard implementation for the filtering of checkbox columns. The only available operators are the equal and the general null and not null operators.
The DgvDateColumnFilter Class
A standard implementation for the filtering of date columns.
The DgvComboBoxColumnFilter Class
A standard implementation for the filtering of combobox columns. By default, on textbox columns, the filter manager uses DgvTextBoxColumnFilter instances. However, you can force an instance of DgvComboBoxColumnFilter on such columns. In this case, the DgvComboBoxColumnFilter instance automatically creates a distinct list of values from the column data. You should do an explicit call to the RefreshValues() method when the underlying data changes.
Customizing
If "one line usage" is not sufficient for your needs, you can control the process of adding and showing filters in different ways.
Using a DgvComboBoxColumnFilter for Non-Combobox Columns
Use one of the manager indexers to access the filter, and assign it an instance of the DgvComboBoxColumnFilter class.
DgvFilterManager fm = new DgvFilterManager(dataGridView1);
fm["CustomerID"] = new DgvComboBoxColumnFilter();
Using Events
ColumnFilterAdding
Using this manager event, you may force your preferred filter before the manager creates the predefined filter. The event is raised for each column in the grid when you set the DataGridView property.
...
DgvFilterManager fm = new DgvFilterManager();
fm.ColumnFilterAdding += new ColumnFilterEventHandler(fm_ColumnFilterAdding);
fm.DataGridView = dataGridView1;
...
void fm_ColumnFilterAdding(object sender, ColumnFilterEventArgs e) {
if (e.Column.Name == "CustomerID") {
e.ColumnFilter = new DgvComboBoxColumnFilter();
}
}
PopupShowing
This manager event allows you to customize the filter host position when popped up.
...
DgvFilterManager fm = new DgvFilterManager();
fm.DataGridView = dataGridView1;
fm.PopupShowing += new ColumnFilterEventHandler(fm_PopupShowing);
...
void fm_PopupShowing(object sender, ColumnFilterEventArgs e) {
DgvFilterManager fm = ((DgvFilterManager)sender);
Rectangle HeaderRectangle =
fm.DataGridView.GetCellDisplayRectangle(e.Column.Index,-1,true);
fm.FilterHost.Popup.Show(fm.DataGridView, HeaderRectangle.Left,
HeaderRectangle.Bottom);
e.Handled = true;
}
FilterExpressionBuilding
Using the DgvBaseColumnFilter event, you can customize the filter expression building process. In the following code example, we add new operators and then manage them in the event handler. The FilterExpression and FilterCaption properties will be used by the manager to build the whole filter and to set the column caption.
...
DgvDateColumnFilter OrderDate;
...
DgvFilterManager fm = new DgvFilterManager(dataGridView1);
fm.DataGridView = dataGridView1;
OrderDate = ((DgvDateColumnFilter)fm["OrderDate"]);
OrderDate.ComboBoxOperator.Items.Insert(0, "This year");
OrderDate.ComboBoxOperator.Items.Insert(1, "1 year ago");
OrderDate.ComboBoxOperator.Items.Insert(2, "2 years ago");
OrderDate.FilterExpressionBuilding +=
new CancelEventHandler(OrderDate_FilterExpressionBuilding);
...
void OrderDate_FilterExpressionBuilding(object sender, CancelEventArgs e) {
int index = OrderDate.ComboBoxOperator.SelectedIndex;
if (index < 3) {
int year = (DateTime.Today.Year - index);
OrderDate.FilterExpression = "(OrderDate>='" + year.ToString() + "-1-1' "
+ "AND OrderDate<='" + year.ToString() + "-12-31') ";
OrderDate.FilterCaption = OrderDate.OriginalDataGridViewColumnHeaderText
+ "\n = year " + year.ToString();
e.Cancel = true;
}
}
Subclassing
A more powerful way to customize your filters is through subclassing. You should think of the proposed standard implementations of DgvBaseFilterHost and DgvBaseColumnFilter as just some possible implementations.
Creating Your Own Host
As said above, derive from DgvBaseFilterHost and provide some visual elements. Add a container within your control to host the child filter controls, and return it by an override of the FilterClientArea property. The base class provides the necessary logic to cooperate with the manager, and provides some facilities helping to position the child filter controls and to adjust the host size. Another facility simplifies the creation of transparent skinned hosts, thanks to the method BitmapToRegion I've found in a very nice article by John O'Byrne.
Note: A skinned host must be constrained to a fixed size. Be sure to inhibit the resize logic by overriding the DoAutoFit method. Also, keep in mind this limitation when designing your own host and your filters.
DgvFilterManager fm = new DgvFilterManager();
fm.FilterHost = new CustomizedFilterHost();
fm.DataGridView = dataGridView1;
Creating Your Own Column Filters
Creating new column filters is simple. Derive from DgvBaseColumnFilter and add your visual elements. Override OnFilterExpressionBuilding to provide filter building logic and, using DataView.RowFilter rules, assign a value to the FilterExpression property and a title to the FilterCaption property.
Remember that the filter is applied when the user clicks on the OK button of the host. However, you can obtain an immediate filter application doing a call to the RebuildFilter method of the filter manager.
New Filters
To satisfy some requests, in the 1.1.0.0 update, I've introduced three new filter implementations:
The DgvMonthYearColumnFilter Class
This filter allows the user to select a month and a year. By setting the YearMin and YearMax properties, you can control the shown years range. Month names default to English, but you may provide culture-specific names by once setting the value of the static property MonthCsvList with a comma separated list of month names.
The DgvNumRangeColumnFilter Class
Use this filter to allow the user to specify a range filter on numeric columns.
The DgvDateRangeColumnFilter Class
Use this filter to allow the user to specify a range filter on date columns.
Conclusions
In this article, I've exposed the class architecture and common usage scenarios. This conceptual overview, I hope, will help you understand how it works. For detailed explanations and references, you can see the attached documentation.
Note: To those interested in documenting their works, I've used these materials:
History
- 1.1.0.0 (19 Mar 2009)
- Added three new embedded filters:
DgvDateRangeColumnFilter, DgvMonthYearColumnFilter, and DgvNumRangeColumnFilter. - It's now possible to dynamically change the
DataSource.
- 1.0.0.1 (04 Mar 2009)
- Fix: Filters are now applied when the grid is bound to a
BindingSource which uses a DataSet as the first source.
- 1.0.0.0 (01 Mar 2009)
