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How to: Handle Errors and Exceptions that Occur with Databinding

Oftentimes exceptions and errors occur on the underlying business objects when you bind them to controls. You can intercept these errors and exceptions and then either recover or pass the error information to the user by handling the BindingComplete event for a particular Binding, BindingSource, or CurrencyManager component.

This code example demonstrates how to handle errors and exceptions that occur during a data-binding operation. It demonstrates how to intercept errors by handling the Binding.BindingComplete event of the Binding objects. In order to intercept errors and exceptions by handling this event, you must enable formatting for the binding. You can enable formatting when the binding is constructed or added to the binding collection, or by setting the FormattingEnabled property to true.

using System;
using System.Drawing;
using System.Windows.Forms;

class Form1 : Form
{
	private BindingSource BindingSource1 = new BindingSource();
	private TextBox textBox1 = new TextBox();
	private TextBox textBox2 = new TextBox();
	private TextBox textBox3 = new TextBox();

	public Form1()
	{
		//Set up the textbox controls. 
		this.textBox1.Location = new System.Drawing.Point(82, 13);
		this.textBox1.TabIndex = 1;
		this.textBox2.Location = new System.Drawing.Point(81, 47);
		this.textBox2.TabIndex = 2;
		this.textBox3.Location = new System.Drawing.Point(81, 83);
		this.textBox3.TabIndex = 3;

		// Add the textbox controls to the form 
		this.Controls.Add(this.textBox2);
		this.Controls.Add(this.textBox1);
		this.Controls.Add(this.textBox3);

		// Handle the form's Load event. 
		this.Load += new System.EventHandler(this.Form1_Load);
	}
	Binding partNameBinding;
	Binding partNumberBinding;

	private void Form1_Load(object sender, EventArgs e)
	{
		// Set the DataSource of BindingSource1 to the Part type.
		BindingSource1.DataSource = typeof(Part);

		// Bind the textboxes to the properties of the Part type,  
		// enabling formatting.
		partNameBinding = textBox1.DataBindings.Add("Text",
			BindingSource1, "PartName", true);
		
		partNumberBinding = textBox2.DataBindings.Add("Text", BindingSource1, "PartNumber",
			true);

		//Bind the textbox to the PartPrice value with currency formatting.
		textBox3.DataBindings.Add("Text", BindingSource1, "PartPrice", true,
			DataSourceUpdateMode.OnPropertyChanged, 0, "C");
			

		// Handle the BindingComplete event for BindingSource1 and  
		// the partNameBinding.
		partNumberBinding.BindingComplete +=
			new BindingCompleteEventHandler(partNumberBinding_BindingComplete);
		partNameBinding.BindingComplete +=
			new BindingCompleteEventHandler(partNameBinding_BindingComplete);

		// Add a new part to BindingSource1.
		BindingSource1.Add(new Part("Widget", 1234, 12.45));
	}

	// Handle the BindingComplete event to catch errors and exceptions  
	// in binding process. 
	void partNumberBinding_BindingComplete(object sender,
		BindingCompleteEventArgs e)
	{
		if (e.BindingCompleteState != BindingCompleteState.Success)
			MessageBox.Show("partNumberBinding: " + e.ErrorText);
	}		

	// Handle the BindingComplete event to catch errors and  
	// exceptions in binding process. 
	void partNameBinding_BindingComplete(object sender,
		BindingCompleteEventArgs e)
	{
		if (e.BindingCompleteState != BindingCompleteState.Success)
			MessageBox.Show("partNameBinding: " + e.ErrorText);
	}

	[STAThread]
	static void Main()
	{
		Application.EnableVisualStyles();
		Application.Run(new Form1());
	}
}

// Represents a business object that throws exceptions when invalid values are 
// entered for some of its properties. 
public class Part
{
	private string name;
	private int number;
	private double price;

	public Part(string name, int number, double price)
	{
		PartName = name;
		PartNumber = number;
		PartPrice = price;
	}

	public string PartName
	{
		get { return name; }
		set
		{
			if (value.Length <= 0)
				throw new Exception("Each part must have a name.");
			else
				name = value;
		}
	}
	public double PartPrice
	{
		get { return price; }
		set { price = value; }
	}

	public int PartNumber
	{
		get { return number; }
		set
		{
			if (value < 100)
				throw new Exception("Invalid part number." +
					" Part numbers must be greater than 100.");
			else
				number = value;
		}
	}
}

When the code is running and an empty string is entered for the part name or a value less than 100 is entered for the part number, a message box appears. This is a result of handling the Binding.BindingComplete event for these textbox bindings.

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