| # 26. Data Binding One common question we get from our users is: Can I still take advantage of data aware control mechanisms with my objects? The answer is quite simply yes. .NET data binding also works with plain objects. This is also to say that using db4o is completely orthogonal to the use of data binding. The usual pattern would be something like the following: * the code asks db4o to retrieve the objects that must be presented to the user; * the UI controls are bound to the objects (no interaction with db4o here); * the user interacts with the objects through the controls (no interaction with db4o here); * when the user is done interacting with the objects or by his request, the application will ask db4o to persist his changes; Let's take a very simple example that illustrates the points above. Our business class:
`namespace CSDataBinding { /// <summary> /// A simple business class. /// </summary> public class Customer { string _name; string _phoneNumber; public Customer(string name, string phoneNumber) { _name = name; _phoneNumber = phoneNumber; } public string Name { get { return _name; } set { _name = value; } } public string PhoneNumber { get { return _phoneNumber; } set { _phoneNumber = value; } } } }`
The Form class:
`using System; using System.Drawing; using System.Collections; using System.ComponentModel; using System.IO; using System.Windows.Forms; using com.db4o; namespace CSDataBinding { /// <summary> /// DataBinding form example /// </summary> public class MainForm : System.Windows.Forms.Form { internal System.Windows.Forms.TextBox _txtPhoneNumber; internal System.Windows.Forms.ComboBox _cmbCustomers; /// <summary> /// Required designer variable. /// </summary> private System.ComponentModel.Container components = null; internal System.Windows.Forms.Label _labelPhone; internal System.Windows.Forms.Label _labelName; private ObjectContainer _container = null; private ArrayList _customers = new ArrayList(); public MainForm() { // // Required for Windows Form Designer support // InitializeComponent(); OpenDataFile(); SetUpDataBindings(); } void OpenDataFile() { string dataFile = Path.Combine(Application.UserAppDataPath, "data.yap"); _container = Db4o.openFile(dataFile); } void SetUpDataBindings() { ObjectSet os = _container.get(typeof(Customer)); if (0 == os.size()) { // Generate some initial data _customers.Add(new Customer("John Cleese", "55-98763333")); _customers.Add(new Customer("Herman Hesse","32-33335555")); _customers.Add(new Customer("Douglas Adams", "42-42424242")); } else { while (os.hasNext()) { _customers.Add(os.next()); } } _cmbCustomers.DisplayMember = "Name"; _cmbCustomers.DataSource = _customers; _txtPhoneNumber.DataBindings.Add("Text", _customers, "PhoneNumber"); } void PersistChanges() { foreach (Customer customer in _customers) { _container.set(customer); } } protected override void OnClosing(CancelEventArgs e) { PersistChanges(); _container.close(); base.OnClosing (e); } /// <summary> /// Clean up any resources being used. /// </summary> protected override void Dispose( bool disposing ) { if( disposing ) { if (components != null) { components.Dispose(); } } base.Dispose( disposing ); } #region Windows Form Designer generated code /// <summary> /// Required method for Designer support - do not modify /// the contents of this method with the code editor. /// </summary> private void InitializeComponent() { this._labelPhone = new System.Windows.Forms.Label(); this._txtPhoneNumber = new System.Windows.Forms.TextBox(); this._labelName = new System.Windows.Forms.Label(); this._cmbCustomers = new System.Windows.Forms.ComboBox(); this.SuspendLayout(); // // _labelPhone // this._labelPhone.Location = new System.Drawing.Point(8, 48); this._labelPhone.Name = "_labelPhone"; this._labelPhone.Size = new System.Drawing.Size(72, 16); this._labelPhone.TabIndex = 9; this._labelPhone.Text = "Phone#:"; // // _txtPhoneNumber // this._txtPhoneNumber.Location = new System.Drawing.Point(96, 48); this._txtPhoneNumber.Name = "_txtPhoneNumber"; this._txtPhoneNumber.Size = new System.Drawing.Size(184, 20); this._txtPhoneNumber.TabIndex = 8; this._txtPhoneNumber.Text = ""; // // _labelName // this._labelName.Location = new System.Drawing.Point(8, 16); this._labelName.Name = "_labelName"; this._labelName.Size = new System.Drawing.Size(72, 16); this._labelName.TabIndex = 7; this._labelName.Text = "Customer:"; // // _cmbCustomers // this._cmbCustomers.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left) | System.Windows.Forms.AnchorStyles.Right))); this._cmbCustomers.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList; this._cmbCustomers.Location = new System.Drawing.Point(96, 16); this._cmbCustomers.Name = "_cmbCustomers"; this._cmbCustomers.Size = new System.Drawing.Size(186, 21); this._cmbCustomers.TabIndex = 6; // // MainForm // this.AutoScaleBaseSize = new System.Drawing.Size(5, 13); this.ClientSize = new System.Drawing.Size(290, 79); this.Controls.Add(this._labelPhone); this.Controls.Add(this._txtPhoneNumber); this.Controls.Add(this._labelName); this.Controls.Add(this._cmbCustomers); this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle; this.Name = "MainForm"; this.Text = "Db4o Data Binding"; this.ResumeLayout(false); } #endregion /// <summary> /// The main entry point for the application. /// </summary> [STAThread] static void Main() { Application.Run(new MainForm()); } } }`
There are also some good tutorials on the the use of Forms data binding [1], unfortunately most of them are focused only on binding controls to relational databases. We - the software development community - still suffer from database atrophy[2] after all. We - the db4o team along with the object oriented community - are working to change that so we can finally move on to the next level. [1] http://samples.gotdotnet.com/quickstart/winforms/doc/winformsdata.aspx [2] http://www.people4objects.org/Klaus/2005/01/database-atrophy.html -- generated by Doctor courtesy of db4objects Inc.