Why use bindingsource

Here's what you'll do: The authors grid will have a straightforward binding to the authors table through its BindingSource. Likewise, the titles grid will have a similar binding for the titles table. You'll set up an additional BindingSource for the titleauthor table as a child binding on the authors BindingSource. Then, whenever the list changes for the titleauthor BindingSource which will happen whenever a new author is selected in the author grid through the master-details mechanisms , you'll set up a new filter criteria for the titles BindingSource to only show the related titles.

Listing 2 shows the complete form code that sets all this up. It then binds the authors and titles grids to their respective BindingSource objects.

The authors and titles BindingSources are bound to their respective tables in the dataset. You can ignore the publishers binding code for now; that will be discussed in the next section. Finally, the Load event handler wires up some event handlers for events raised by the BindingSource objects. The BindingComplete and ListChanged events are raised by a BindingSource object when the data binding process is complete against its underlying data source, and when the contents of the list it manages have changed, respectively.

You could have also done the same against the authors table, instead monitoring the CurrentChanged event. The event subscriptions are done in Listing 2 using a new C language feature called delegate inference. You can simply set the event subscription to the name of the handler method, and the compiler will worry about creating an instance of an appropriate delegate to add to the event's subscriber list.

The event handlers just described call a helper method called BindTitles. You won't hear it called that often, but another common requirement in data binding is to provide a display mechanism for many-to-one relations between collections of data. This is basically synchronizing from a selection in a collection of child items to update another control that will display the corresponding parent item.

The easiest way to do this is to tap into the events raised by a BindingSource again. The code I skipped over in the Load event handler of Listing 2 sets up a data binding between the publishers table and the textbox at the bottom of the form that displays the publisher name for the currently selected title in the titles grid. The Add method on the DataBindings collection of a control creates a new Binding object and adds it to the collection of bindings for that control.

Whatever item is current in the data source will automatically be displayed in the TextBox , and any edits to the text will be pushed back into the underlying data source when the focus leaves the control.

With just those two lines of code, there is no synchronization set up between selected titles and the publishers. There are a couple of ways to achieve that synchronization.

One would be to not even bother with data binding as shown above, but simply set the Text property of the TextBox directly based on row selections in the titles grid. In that event handler, you could just navigate to the parent row using the properties exposed on a typed data set, and use it to set the TextBox value. However, if you want to stick with a data bound approach, you can again use the filtering capabilities of BindingSources to filter the publishers list down to only the matching row.

Sometimes the way the data is stored in the data source is not exactly how you want to display it. For example, you may want to format a date-time string, or take a raw image stored in the database and turn it into a Bitmap object for binding against a PictureBox control.

The way you dealt with these kinds of situations in the past was to handle the Format and Parse events on the Binding object for simple bound controls, or to handle control-level events for DataGrid or ComboBox controls to intercept the data as it was being bound. You can still use those events for specialized situations, but in. The Binding class now has a number of new overloads and properties that let you influence automatic formatting that is done by the class as it grabs values out of the data source and before it sets the corresponding property on the bound control.

You can set format strings or provide your own format provider. You can also influence when the formatting occurs. Parsing follows a reverse process and just works in many common cases. All you need to do to support this is set a few extra pieces of information on the Binding object before you add it to the DataBindings collection of the TextBox :. The fourth argument to the Binding constructor turns automatic formatting on. You can then provide a format string if the type being formatted DateTime in this case has a default formatter that will know what to do with the string you provide.

If not, there is a FormatProvider property that you can set to provide a specialized formatter. As you can see, you can also specify what value should be displayed for DBNull values, and if that same value is read back in while parsing, a DBNull will be placed in the underlying data source.

The automatic formatting will try to find a type converter to use if the bound property is not a string. For example, if the bound property type is Image, and the value in the data source is a byte array, there is a default type converter for image that takes the byte array and tries to convert it to an Image instance by serializing the bytes back in. You can do a lot more through the synchronization mechanisms of BindingSource and Binding objects, and through the formatting capabilities of Binding objects.

Then run the application. Now we will perform an operation using methods of the BindingSource class. Add some buttons and change the text. Write the following code. Generic; using System. ComponentModel; using System. Data; using System. Drawing; using System. Linq; using System. Text; using System. You can move, or remove it, as needed. Fill this. Initially it will show the first record. Click the "Next" button.

There seem to be a variety of different ways to do data binding, but I couldn't find them spelled out anywhere. So, I did a little experimentation to learn several of the things you can do.

Let's start with the typical case: you assign a BindingSource object as the DataSource of a control. You can think of BindingSource as a "2-in-1" data source. It has:. Tip : In this tutorial, we will often add a binding to the " Text " property of TextBox es.

Other common bindings you may add to DataBindings include:. Only DataGrid is available in the. NET Compact Framework, however. Some articles on CodeProject propose ways to overcome this limitation, however. Most examples here are given using an object-based data source, because maybe I'm prejudiced against databases. Suppose you have a class with some data in it:. Well, sorry, but the above classes won't work.

There's nothing to bind to here, because the data has to be provided in the form of properties, not methods or fields.

And, I'm guessing they have to be public non-static properties, though I haven't checked. So, let's try again:. That's better. Suppose you put this in your project, and you want to have a DataGridView that shows a list of Airplane s. And, you want a TextBox where the user can change the Model name of the currently selected Airplane.

It is typical to set up data bindings in the Visual Studio designer. If you want to follow along, create a new Windows Forms project, and create a C code file with the above Airplane and Passenger classes in it. If you select your DataGridView , there's a little tiny arrow in the top-right corner that you can click to find a configuration box. Note : the wizard won't see Airplane and Passenger until the project is built.

You can tell this wizard to get the data from an " Object ", and on the second page, you can select Airplane from a tree. The wizard will create a BindingSource in the component tray and set its DataSource to typeof Airplane :. There is no column for the passengers list, however; I guess the wizard knows you can't show a list of complex objects within a single cell. You can show a dropdown list of strings within a cell, but I don't discuss that in this article.

In the properties of the TextBox , open up the " Data Bindings " node, click the " Advanced " line, then click " Choose the Text property, and then open up the "Binding" list where you can select the Model property of airplaneBindingSource :.

Then, click OK. Now, all you have to do is add some airplanes to the list. This is done by adding Airplane s to the BindingSource. Other controls are not so smart. For example, if the Model were read-only, the user would still be allowed to change txtModel.

To prevent this, you would have to manually set txtModel. All is well, but personally, I like to set up the binding in the code. So humor me. Let's start over. In the designer, delete airplaneBindingSource , and the controls will suddenly be unbound again. Note that we have to define our own BindingSource because we deleted the one in the designer. Anyway, run the program, and you should get the same thing as before:.

Again, the DataGridView knows it can't create a column for Airplane. This was easier than using the wizards, wasn't it? With only five more lines of code, you no longer need to set it up in the designer. On the other hand, the designer makes it easier to customize the columns. NET control for headings and labels. The ProBindingSource determines headings and labels by using either the column label if defined , the field label if defined , or the field name from the schema.

If the. Define a trigger to handle a SortRequest event. Binding to a ProDataSet object Binding to a ProDataSet object enables you to create a hierarchical display of a parent buffer and its child buffers in the same. When binding to a ProDataSet object, consider the following: The ProDataSet object can contain one or more parent and child buffers and a set of data relations describing the relationship between the parent and child buffers.

The ProDataSet object can be either static or dynamic. You use a handle to access either a static or dynamic ProDataSet object. You can identify a temp-table in a ProDataSet object by either its name or its handle. To bind a hierarchy of parent and child buffers to a single. NET control, specify a parent buffer from the ProDataSet object as the top-level table to display in the. NET control. A parent buffer is typically a top-level buffer in the ProDataSet object, but it need not be.

Any child buffers of the specified parent buffer are automatically included in the hierarchy. The ProBindingSource makes a buffer's data available to a bound. NET control as follows: If you specify a parent buffer that is a top-level buffer, the ProBindingSource uses the buffer's top-level navigation query specified by the TOP-NAV-QUERY attribute to populate the primary set of records, and uses the data-relation queries associated with each of the child buffers for subsequent levels.

If you specify a parent buffer that is not a top-level buffer, the ProBindingSource uses the buffer's data-relation query to populate the primary set of records, and uses the data-relation queries associated with each of the child buffers for subsequent levels.

If you specify a buffer that is not a parent buffer that is, a buffer that has no child buffers , the ProBindingSource binds to a single table.

To display both parent and child buffers within the same. To display the parent and child buffers in separate. The ProBindingSource automatically changes currency in the parent buffer as reflected by the Position property as the selected parent or child row in the bound.

NET control changes. When the user first expands not selects a parent row in the bound. NET control, all of the child rows for that parent row are displayed.

The ProBindingSource uses the ProDataSet object's data-relation query to create and maintain a unique query for all child rows related to the expanded parent row. For example, if the user expands multiple parent rows, there will be an open child query for each expanded parent row based on the corresponding parent record. The ProBindingSource takes information from the ProDataSet object schema definition and makes it available to the bound.