vb.net barcode generator open source Wiring the Save Button in C#

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Wiring the Save Button
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The DataGridView control will let us add, modify, and delete data in the table itself, but these changes won t be passed to the database until we call the SaveChanges method on the entity framework data context object. To do this, we are going to wire up the button that was added to the toolbar earlier in the process. The button, which is highlighted in Figure 32-24, is disabled by default when it is created.
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Figure 32-24. The disabled Save button To enable the button, select it and change the value of the Enabled property to True. You ll see it brighten on the design surface. Now double-click the button to create an event handler for the Click event. The display will switch to the code-behind file, and you will see a new method has been added. Add a statement to save the changes in the Entity Framework data, as shown in Listing 32-7. Listing 32-7. Saving Data in the Code-Behind File using System.Windows.Forms; namespace DataApp { public partial class Form1 : Form { // define the EntityFramework context field NorthwindEntities entityContext = new NorthwindEntities(); public Form1() { InitializeComponent(); // set the data source for the data binding employeeBindingSource.DataSource = entityContext.Employees; } private void employeeBindingNavigatorSaveItem Click(object sender, System.EventArgs e) { entityContext.SaveChanges(); } } } The name of your method may be slightly different from mine, but the statement you must add is the same and is shown in bold in the listing. Wiring up the button like this means that any changes we made are saved when we click the button.
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Testing the Program
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All that remains is to compile and run the program. The data will be loaded automatically from the database and displayed in the window, as shown by Figure 32-25.
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Figure 32-25. The data-driven Windows Forms program We get a lot of functionality for very little effort. You can move through the data using the backward and forward arrows, and if there is more data than can be fit on the screen, it will be automatically grouped into pages that you can move through. We can add records by clicking the plus button and delete the current records by clicking the cross button. We can modify any field by double-clicking it and entering a new value. And all of these changes can be saved to the database by clicking the Save button that we wired up. In fact, we can build a simple but functional data-driven program in about ten minutes. Most of which is spent setting up the database and creating the data model.
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In the following sections, I show you two simple variations that widen the possibilities offered by the data support in Windows Forms, and even then, we are still only skimming the surface. The way that controls can display data is very rich indeed, and I recommend exploring further.
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Filtering the Data with LINQ
In the sample, we displayed all the rows in the Employee database, but we can easily filter the data by using a LINQ query as the data source for the BindingSource control. Listing 32-8 demonstrates this, applied to the code-behind file. Listing 32-8. Using a LINQ Query to Filter Data using System.Windows.Forms; using System.Linq; namespace DataApp { public partial class Form1 : Form { // define the EntityFramework context field
CHAPTER 32 WINDOWS FORMS
NorthwindEntities entityContext = new NorthwindEntities(); public Form1() { InitializeComponent(); // set the data source for the data binding employeeBindingSource.DataSource = entityContext.Employees .Where(e => e.City == "London") .Select(e => e); } private void employeeBindingNavigatorSaveItem Click(object sender, System.EventArgs e) { entityContext.SaveChanges(); } } } The LINQ query in the listing filters the Employee objects so that only those with a City value of London will be selected. The effect of using this query is shown in Figure 32-26. You can use any LINQ to Entities query as the data source, but you must be careful to match the data type projected by your query to the one that you used to create and populate the grid columns.
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