Cómo: Determinar si un formato de datos está presente en un objeto de datos
En los ejemplos siguientes se muestra cómo utilizar las diversas sobrecargas del método GetDataPresent para consultar si un formato de datos determinado se encuentra en un objeto de datos.
Ejemplo
Descripción
En el ejemplo de código siguiente, se usa la sobrecarga del método GetDataPresent(String) para consultar la presencia de un formato de datos concreto por cadena del descriptor.
Código
Dim dataObject As New DataObject("Some string data to store...")
' Query for the presence of Text data in the data object, by a data format descriptor string.
' In this overload of GetDataPresent, the method will return true both for native data formats
' and when the data can automatically be converted to the specifed format.
' In this case, string data is present natively, so GetDataPresent returns "true".
Dim textData As String = Nothing
If dataObject.GetDataPresent(DataFormats.StringFormat) Then
textData = TryCast(dataObject.GetData(DataFormats.StringFormat), String)
End If
' In this case, the Text data in the data object can be autoconverted to
' Unicode text, so GetDataPresent returns "true".
Dim unicodeData() As Byte = Nothing
If dataObject.GetDataPresent(DataFormats.UnicodeText) Then
unicodeData = TryCast(dataObject.GetData(DataFormats.UnicodeText), Byte())
End If
DataObject dataObject = new DataObject("Some string data to store...");
// Query for the presence of Text data in the data object, by a data format descriptor string.
// In this overload of GetDataPresent, the method will return true both for native data formats
// and when the data can automatically be converted to the specifed format.
// In this case, string data is present natively, so GetDataPresent returns "true".
string textData = null;
if (dataObject.GetDataPresent(DataFormats.StringFormat))
{
textData = dataObject.GetData(DataFormats.StringFormat) as string;
}
// In this case, the Text data in the data object can be autoconverted to
// Unicode text, so GetDataPresent returns "true".
byte[] unicodeData = null;
if (dataObject.GetDataPresent(DataFormats.UnicodeText))
{
unicodeData = dataObject.GetData(DataFormats.UnicodeText) as byte[];
}
Ejemplo
Descripción
En el ejemplo de código siguiente, se usa la sobrecarga del método GetDataPresent(Type) para consultar la presencia de un formato de datos concreto por tipo.
Código
Dim dataObject As New DataObject("Some string data to store...")
' Query for the presence of String data in the data object, by type. In this overload
' of GetDataPresent, the method will return true both for native data formats
' and when the data can automatically be converted to the specifed format.
' In this case, the Text data present in the data object can be autoconverted
' to type string (also represented by DataFormats.String), so GetDataPresent returns "true".
Dim stringData As String = Nothing
If dataObject.GetDataPresent(GetType(String)) Then
stringData = TryCast(dataObject.GetData(DataFormats.Text), String)
End If
DataObject dataObject = new DataObject("Some string data to store...");
// Query for the presence of String data in the data object, by type. In this overload
// of GetDataPresent, the method will return true both for native data formats
// and when the data can automatically be converted to the specifed format.
// In this case, the Text data present in the data object can be autoconverted
// to type string (also represented by DataFormats.String), so GetDataPresent returns "true".
string stringData = null;
if (dataObject.GetDataPresent(typeof(string)))
{
stringData = dataObject.GetData(DataFormats.Text) as string;
}
Ejemplo
Descripción
En el ejemplo siguiente, se usa la sobrecarga del método GetDataPresent(String, Boolean) para consultar los datos por cadena del descriptor y especificar cómo tratar los formatos de datos de autoconversión.
Código
Dim dataObject As New DataObject("Some string data to store...")
' Query for the presence of Text data in the data object, by data format descriptor string,
' and specifying whether auto-convertible data formats are acceptable.
' In this case, Text data is present natively, so GetDataPresent returns "true".
Dim textData As String = Nothing
If dataObject.GetDataPresent(DataFormats.Text, False) Then ' Auto-convert?
textData = TryCast(dataObject.GetData(DataFormats.Text), String)
End If
' In this case, the Text data in the data object can be autoconverted to
' Unicode text, but it is not available natively, so GetDataPresent returns "false".
Dim unicodeData() As Byte = Nothing
If dataObject.GetDataPresent(DataFormats.UnicodeText, False) Then ' Auto-convert?
unicodeData = TryCast(dataObject.GetData(DataFormats.UnicodeText), Byte())
End If
' In this case, the Text data in the data object can be autoconverted to
' Unicode text, so GetDataPresent returns "true".
If dataObject.GetDataPresent(DataFormats.UnicodeText, True) Then ' Auto-convert?
unicodeData = TryCast(dataObject.GetData(DataFormats.UnicodeText), Byte())
End If
DataObject dataObject = new DataObject("Some string data to store...");
// Query for the presence of Text data in the data object, by data format descriptor string,
// and specifying whether auto-convertible data formats are acceptable.
// In this case, Text data is present natively, so GetDataPresent returns "true".
string textData = null;
if (dataObject.GetDataPresent(DataFormats.Text, false /* Auto-convert? */))
{
textData = dataObject.GetData(DataFormats.Text) as string;
}
// In this case, the Text data in the data object can be autoconverted to
// Unicode text, but it is not available natively, so GetDataPresent returns "false".
byte[] unicodeData = null;
if (dataObject.GetDataPresent(DataFormats.UnicodeText, false /* Auto-convert? */))
{
unicodeData = dataObject.GetData(DataFormats.UnicodeText) as byte[];
}
// In this case, the Text data in the data object can be autoconverted to
// Unicode text, so GetDataPresent returns "true".
if (dataObject.GetDataPresent(DataFormats.UnicodeText, true /* Auto-convert? */))
{
unicodeData = dataObject.GetData(DataFormats.UnicodeText) as byte[];
}