Como identificar erros e exceções que ocorram na associação de dados

Muitas vezes, erros e exceções ocorrem nos objetos de negócios subjacentes quando você os associa aos controles. Você pode interceptar esses erros e exceções e, em seguida, recuperar ou passar as informações de erro para o usuário manipulando o BindingComplete evento para um determinado Binding, BindingSourceou CurrencyManager componente.

Exemplo

Este exemplo de código demonstra como tratar erros e exceções que ocorrem durante uma operação de associação de dados. Ele demonstra como interceptar erros manipulando o Binding.BindingCompleteBinding evento dos objetos. Para interceptar erros e exceções ao manipular esse evento, você deve habilitar a formatação para a associação. Você pode habilitar a formatação quando a associação é construída ou adicionada à coleção de vinculação ou definindo a FormattingEnabled propriedade como 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.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

Quando o código está em execução e uma cadeia de caracteres vazia é inserida para o nome da peça ou um valor menor que 100 é inserido para o número de peça, uma caixa de mensagem será exibida. Isso é resultado da manipulação do Binding.BindingComplete evento para essas associações de caixa de texto.

Compilando o código

Este exemplo requer:

• Referências aos assemblies System, System.Drawing e System.Windows.Forms.

Confira também

• Binding.BindingComplete
• BindingSource.BindingComplete
• Componente BindingSource