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.

Example

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.

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

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

    property String^ PartName 
    {
        String^ get()
        {
            return name;
        }

        void set(String^ value)
        {
            if (value->Length <= 0)
            {
                throw gcnew Exception(
                    "Each part must have a name.");
            }
            else
            {
                name = value;
            }
        }
    }

    property double PartPrice 
    {
        double get()
        {
            return price;
        }

        void set(double value)
        {
            price = value;
        }
    }

    property int PartNumber 
    {
        int get()
        {
            return number;
        }

        void set(int value)
        {
            if (value < 100)
            {
                throw gcnew Exception(
                    "Invalid part number." \
                    "Part numbers must be " \
                    "greater than 100.");
            }
            else
            {
                number = value;
            }
        }
    }

};

ref class MainForm: public Form
{
private:
    BindingSource^ bindingSource;
    TextBox^ partNameTextBox;
    TextBox^ partNumberTextBox;
    TextBox^ partPriceTextBox;

public:
    MainForm()
    {
        bindingSource = gcnew BindingSource;
        partNameTextBox = gcnew TextBox;
        partNumberTextBox = gcnew TextBox;
        partPriceTextBox = gcnew TextBox;
            
        //Set up the textbox controls.
        this->partNameTextBox->Location = Point(82, 13);
        this->partNameTextBox->TabIndex = 1;
        this->partNumberTextBox->Location = Point(81, 47);
        this->partNumberTextBox->TabIndex = 2;
        this->partPriceTextBox->Location = Point(81, 83);
        this->partPriceTextBox->TabIndex = 3;
        
        // Add the textbox controls to the form
        this->Controls->Add(this->partNumberTextBox);
        this->Controls->Add(this->partNameTextBox);
        this->Controls->Add(this->partPriceTextBox);
        
        // Handle the form's Load event.
        this->Load += gcnew EventHandler(this, 
            &MainForm::OnMainFormLoad);
    }

private:

    void OnMainFormLoad(Object^ sender, EventArgs^ e)
    {   
        // Set the DataSource of bindingSource to the Part type.
        bindingSource->DataSource = Part::typeid;
        
        // Bind the textboxes to the properties of the Part type,
        // enabling formatting.
        partNameTextBox->DataBindings->Add(
            "Text", bindingSource, "PartName", true);
        partNumberTextBox->DataBindings->Add(
            "Text", bindingSource, "PartNumber", true);
        
        //Bind the textbox to the PartPrice value 
        // with currency formatting.
        partPriceTextBox->DataBindings->Add("Text", bindingSource, "PartPrice", true,
           DataSourceUpdateMode::OnPropertyChanged, nullptr, "C");

        // Handle the BindingComplete event for bindingSource and
        // the partNameBinding.
        bindingSource->BindingComplete += 
            gcnew BindingCompleteEventHandler(this, 
            &MainForm::OnBindingSourceBindingComplete);
        bindingSource->BindingComplete += 
            gcnew BindingCompleteEventHandler(this, 
            &MainForm::OnPartNameBindingBindingComplete);
        
        // Add a new part to bindingSource.
        bindingSource->Add(gcnew Part("Widget", 1234, 12.45));
    }

    // Handle the BindingComplete event to catch errors and 
    // exceptions in binding process.
    void OnBindingSourceBindingComplete(Object^ sender, 
        BindingCompleteEventArgs^ e)
    {
        if (e->BindingCompleteState == 
            BindingCompleteState::Exception)
        {
            MessageBox::Show(String::Format(
                CultureInfo::CurrentCulture,
                "bindingSource: {0}", e->Exception->Message));
        }

        if (e->BindingCompleteState == 
            BindingCompleteState::DataError)
        {
            MessageBox::Show(String::Format(
                CultureInfo::CurrentCulture,
                "bindingSource: {0}", e->Exception->Message));
        }
    }

    // Handle the BindingComplete event to catch errors and 
    // exceptions in binding process.
    void OnPartNameBindingBindingComplete(Object^ sender, 
        BindingCompleteEventArgs^ e)
    {
        if (e->BindingCompleteState == 
            BindingCompleteState::Exception)
        {
            MessageBox::Show(String::Format(
                CultureInfo::CurrentCulture,
                "PartNameBinding: {0}", e->Exception->Message));
        }

        if (e->BindingCompleteState == 
            BindingCompleteState::DataError)
        {
            MessageBox::Show(String::Format(
                CultureInfo::CurrentCulture,
                "PartNameBinding: {0}", e->Exception->Message));
        }
    }
};

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;
		}
	}
}
Imports System
Imports System.Drawing
Imports System.Windows.Forms

Class Form1
    Inherits Form

    Private  BindingSource1 As New BindingSource()
    Private textBox1 As New TextBox()
    Private textBox2 As New TextBox()
    Private textBox3 As New TextBox()

    Public Sub New()

        'Set up the textbox controls.
        Me.textBox1.Location = New System.Drawing.Point(82, 13)
        Me.textBox1.TabIndex = 1
        Me.textBox2.Location = New System.Drawing.Point(81, 47)
        Me.textBox2.TabIndex = 2
        Me.textBox3.Location = New System.Drawing.Point(81, 83)
        Me.textBox3.TabIndex = 3

        ' Add the textbox controls to the form
        Me.Controls.Add(Me.textBox2)
        Me.Controls.Add(Me.textBox1)
        Me.Controls.Add(Me.textBox3)

    End Sub

    Private WithEvents partNameBinding As Binding
    Private WithEvents partNumberBinding As Binding

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) _
        Handles Me.Load

        ' Set the DataSource of BindingSource1 to the Part type.
        BindingSource1.DataSource = GetType(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")

        ' Add a new part to BindingSource1.
        BindingSource1.Add(New Part("Widget", 1234, 12.45))
    End Sub

    ' Handle the BindingComplete event to catch errors and exceptions 
    ' in binding process.
    Sub partNumberBinding_BindingComplete(ByVal sender As Object, _
        ByVal e As BindingCompleteEventArgs) _
        Handles partNumberBinding.BindingComplete

        If Not e.BindingCompleteState = BindingCompleteState.Success Then
            MessageBox.Show("partNumberBinding: " + e.ErrorText)
        End If

    End Sub

    ' Handle the BindingComplete event to catch errors and exceptions 
    ' in binding process.
    Sub partNameBinding_BindingComplete(ByVal sender As Object, _
        ByVal e As BindingCompleteEventArgs) _
        Handles partNameBinding.BindingComplete

        If Not e.BindingCompleteState = BindingCompleteState.Success Then
            MessageBox.Show("partNameBinding: " + e.ErrorText)
        End If
       
    End Sub

    <STAThread()> _
    Shared Sub Main()
        Application.EnableVisualStyles()
        Application.Run(New Form1())
    End Sub

End Class

' Represents a business object that throws exceptions when invalid 
' values are entered for some of its properties.
Public Class Part
    Private name As String
    Private number As Integer
    Private price As Double

    Public Sub New(ByVal name As String, ByVal number As Integer, _
        ByVal price As Double)

        PartName = name
        PartNumber = number
        PartPrice = price
    End Sub


    Public Property PartName() As String
        Get
            Return name
        End Get
        Set(ByVal value As String)
            If Value.Length <= 0 Then
                Throw New Exception("Each part must have a name.")
            Else
                name = Value
            End If
        End Set
    End Property

    Public Property PartPrice() As Double
        Get
            Return price
        End Get
        Set(ByVal value As Double)
            price = Value
        End Set
    End Property

    Public Property PartNumber() As Integer
        Get
            Return number
        End Get
        Set(ByVal value As Integer)
            If Value < 100 Then
                Throw New Exception("Invalid part number." _
                    & " Part numbers must be greater than 100.")
            Else
                number = Value
            End If
        End Set
    End Property
End Class

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.

Compiling the Code

This example requires:

  • References to the System, System.Drawing and System.Windows.Forms assemblies.

For information about building this example from the command line for Visual Basic or Visual C#, see Building from the Command Line or Command-line Building With csc.exe. You can also build this example in Visual Studio by pasting the code into a new project. Also see How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio.

See Also

Binding.BindingComplete
BindingSource.BindingComplete
BindingSource Component