INullable.IsNull INullable.IsNull INullable.IsNull INullable.IsNull Property

Definition

Gibt an, ob eine Struktur NULL ist.Indicates whether a structure is null. Diese Eigenschaft ist schreibgeschützt.This property is read-only.

public:
 property bool IsNull { bool get(); };
public bool IsNull { get; }
member this.IsNull : bool
Public ReadOnly Property IsNull As Boolean

Eigenschaftswert

SqlBoolean true, wenn der Wert dieses Objekts NULL ist.SqlBoolean true if the value of this object is null. Andernfalls false.Otherwise, false.

Beispiele

Im folgenden Codebeispiel wird eine DataTable mit zwei Spalten erstellt, die als SqlInt32 und SqlString definiert werden.The following code example creates a DataTable with two columns defined as SqlInt32 and SqlString. Der Code fügt eine Zeile mit bekannten Werten und eine Zeile mit NULL-Werten hinzu und durchläuft dann die DataTable. Dabei werden den Variablen die Werte zugewiesen und die Ausgabe im Konsolenfenster angezeigt.The code adds one row of known values, one row of null values and then iterates through the DataTable, assigning the values to variables and displaying the output in the console window.

static private void WorkWithSqlNulls()
{
    DataTable table = new DataTable();

    // Specify the SqlType for each column.
    DataColumn idColumn =
        table.Columns.Add("ID", typeof(SqlInt32));
    DataColumn descColumn =
        table.Columns.Add("Description", typeof(SqlString));

    // Add some data.
    DataRow nRow = table.NewRow();
    nRow["ID"] = 123;
    nRow["Description"] = "Side Mirror";
    table.Rows.Add(nRow);

    // Add null values.
    nRow = table.NewRow();
    nRow["ID"] = SqlInt32.Null;
    nRow["Description"] = SqlString.Null;
    table.Rows.Add(nRow);

    // Initialize variables to use when
    // extracting the data.
    SqlBoolean isColumnNull = false;
    SqlInt32 idValue = SqlInt32.Zero;
    SqlString descriptionValue = SqlString.Null;

    // Iterate through the DataTable and display the values.
    foreach (DataRow row in table.Rows)
    {
        // Assign values to variables. Note that you 
        // do not have to test for null values.
        idValue = (SqlInt32)row["ID"];
        descriptionValue = (SqlString)row["Description"];

        // Test for null value in ID column.
        isColumnNull = idValue.IsNull;

        // Display variable values in console window.
        Console.Write("isColumnNull={0}, ID={1}, Description={2}",
            isColumnNull, idValue, descriptionValue);
        Console.WriteLine();
    }
Private Sub WorkWithSqlNulls()
    Dim table As New DataTable()

    ' Specify the SqlType for each column.
    Dim idColumn As DataColumn = _
      table.Columns.Add("ID", GetType(SqlInt32))
    Dim descColumn As DataColumn = _
      table.Columns.Add("Description", GetType(SqlString))

    ' Add some data.
    Dim row As DataRow = table.NewRow()
    row("ID") = 123
    row("Description") = "Side Mirror"
    table.Rows.Add(row)

    ' Add null values.
    row = table.NewRow()
    row("ID") = SqlInt32.Null
    row("Description") = SqlString.Null
    table.Rows.Add(row)

    ' Initialize variables to use when
    ' extracting the data.
    Dim isColumnNull As SqlBoolean = False
    Dim idValue As SqlInt32 = SqlInt32.Zero
    Dim descriptionValue As SqlString = SqlString.Null

    ' Iterate through the DataTable and display the values.
    For Each row In table.Rows
        ' Assign values to variables. Note that you 
        ' do not have to test for null values.
        idValue = CType(row("ID"), SqlInt32)
        descriptionValue = CType(row("Description"), SqlString)

        ' Test for null value with ID column
        isColumnNull = idValue.IsNull

        ' Display variable values in console window.
        Console.Write("isColumnNull={0}, ID={1}, Description={2}", _
          isColumnNull, idValue, descriptionValue)
        Console.WriteLine()
    Next row
End Sub

In diesem Beispiel werden die folgenden Ergebnisse angezeigt:This example displays the following results:

isColumnNull=False, ID=123, Description=Side Mirror  
isColumnNull=True, ID=Null, Description=Null  

Hinweise

Der Standardwert für alle System.Data.SqlTypes-Instanzen ist NULL.The default value for any System.Data.SqlTypes instance is null. Verwenden IsNull Sie die-Eigenschaft zum Testen auf NULL-Werte.Use IsNull property to test for null values.

Gilt für:

Siehe auch