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QMimeData Class Reference
[QtCore module]

The QMimeData class provides a container for data that records information about its MIME type. More...

 #include <QMimeData>

Inherits QObject.

Public Functions

  • 29 public functions inherited from QObject

Protected Functions

  • virtual QVariant retrieveData ( const QString & mimeType, QVariant::Type type ) const
  • 7 protected functions inherited from QObject

Additional Inherited Members

  • 1 property inherited from QObject
  • 1 public slot inherited from QObject
  • 1 signal inherited from QObject
  • 5 static public members inherited from QObject

Detailed Description

The QMimeData class provides a container for data that records information about its MIME type.

QMimeData is used to describe information that can be stored in the clipboard, and transferred via the drag and drop mechanism. QMimeData objects associate the data that they hold with the corresponding MIME types to ensure that information can be safely transferred between applications, and copied around within the same application.

QMimeData objects are usually created using new and supplied to QDrag or QClipboard objects. This is to enable Qt to manage the memory that they use.

A single QMimeData object can store the same data using several different formats at the same time. The formats() function returns a list of the available formats in order of preference. The data() function returns the raw data associated with a MIME type, and setData() allows you to set the data for a MIME type.

For the most common MIME types, QMimeData provides convenience functions to access the data:

TesterGetterSetterMIME Types
hasText()text()setText()text/plain
hasHtml()html()setHtml()text/html
hasUrls()urls()setUrls()text/uri-list
hasImage()imageData()setImageData()image/ *
hasColor()colorData()setColorData()application/x-color

For example, if your write a widget that accepts URL drags, you would end up writing code like this:

 void MyWidget::dragEnterEvent(QDragEnterEvent *event)
 {
     if (event->mimeData()->hasUrls())
         event->acceptProposedAction();
 }

 void MyWidget::dropEvent(QDropEvent *event)
 {
     if (event->mimeData()->hasUrls()) {
         foreach (QUrl url, event->mimeData()->urls()) {
             ...
         }
     }
 }

There are three approaches for storing custom data in a QMimeData object:

  1. Custom data can be stored directly in a QMimeData object as a QByteArray using setData(). For example:
     QByteArray csvData = ...;

 QMimeData *mimeData = new QMimeData;
 mimeData->setData("text/csv", csvData);
  2. We can subclass QMimeData and reimplement hasFormat(), formats(), and retrieveData().
  3. If the drag and drop operation occurs withing a single application, we can subclass QMimeData and add extra data in it, and use a qobject_cast() in the receiver's drop event handler. For example:
     void MyWidget::dropEvent(QDropEvent *event)
 {
     const MyMimeData *myData =
             qobject_cast<const MyMimeData *>(event->mimeData());
     if (myData) {
         // access myData's data directly (not through QMimeData's API)
     }
 }

Platform-Specific MIME Types

On Windows, formats() will also return custom formats available in the MIME data, using the x-qt-windows-mime subtype to indicate that they represent data in non-standard formats. The formats will take the following form:

 application/x-qt-windows-mime;value="<custom type>"

The following are examples of custom MIME types:

 application/x-qt-windows-mime;value="FileGroupDescriptor"
 application/x-qt-windows-mime;value="FileContents"

The value declaration of each format describes the way in which the data is encoded.

On Windows, the MIME format does not always map directly to the clipboard formats. Qt provides QWindowsMime to map clipboard formats to open-standard MIME formats. Similarly, the QMacPasteboardMime maps MIME to Mac flavors.

See also QClipboard, QDragEnterEvent, QDragMoveEvent, QDropEvent, QDrag, QWindowsMime, QMacPasteboardMime, and Drag and Drop.

Member Function Documentation

QMimeData::QMimeData ()

Constructs a new MIME data object with no data in it.

QMimeData::~QMimeData ()

Destroys the MIME data object.

void QMimeData::clear ()

Removes all the MIME type and data entries in the object.

QVariant QMimeData::colorData () const

Returns a color if the data stored in the object represents a color (MIME type application/x-color); otherwise returns a null variant.

A QVariant is used because QMimeData belongs to the QtCore library, whereas QColor belongs to QtGui. To convert the QVariant to a QColor, simply use qvariant_cast(). For example:

 if (event->mimeData()->hasColor()) {
     QColor color = qvariant_cast<QColor>(event->mimeData()->colorData());
     ...
 }

See also hasColor(), setColorData(), and data().

QByteArray QMimeData::data ( const QString & mimeType ) const

Returns the data stored in the object in the format described by the MIME type specified by mimeType.

See also setData().

QStringList QMimeData::formats () const   [virtual]

Returns a list of formats supported by the object. This is a list of MIME types for which the object can return suitable data. The formats in the list are in a priority order.

For the most common types of data, you can call the higher-level functions hasText(), hasHtml(), hasUrls(), hasImage(), and hasColor() instead.

See also hasFormat(), setData(), and data().

bool QMimeData::hasColor () const

Returns true if the object can return a color (MIME type application/x-color); otherwise returns false.

See also setColorData(), colorData(), and hasFormat().

bool QMimeData::hasFormat ( const QString & mimeType ) const   [virtual]

Returns true if the object can return data for the MIME type specified by mimeType; otherwise returns false.

For the most common types of data, you can call the higher-level functions hasText(), hasHtml(), hasUrls(), hasImage(), and hasColor() instead.

See also formats(), setData(), and data().

bool QMimeData::hasHtml () const

Returns true if the object can return HTML (MIME type text/html); otherwise returns false.

See also setHtml(), html(), and hasFormat().

bool QMimeData::hasImage () const

Returns true if the object can return an image; otherwise returns false.

See also setImageData(), imageData(), and hasFormat().

bool QMimeData::hasText () const

Returns true if the object can return plain text (MIME type text/plain); otherwise returns false.

See also setText(), text(), hasHtml(), and hasFormat().

bool QMimeData::hasUrls () const

Returns true if the object can return a list of urls; otherwise returns false.

URLs correspond to the MIME type text/uri-list.

See also setUrls(), urls(), and hasFormat().

QString QMimeData::html () const

Returns a string if the data stored in the object is HTML (MIME type text/html); otherwise returns an empty string.

See also setHtml(), hasHtml(), and setData().

QVariant QMimeData::imageData () const

Returns a QVariant storing a QImage if the object can return an image; otherwise returns a null variant.

A QVariant is used because QMimeData belongs to the QtCore library, whereas QImage belongs to QtGui. To convert the QVariant to a QImage, simply use qvariant_cast(). For example:

 if (event->mimeData()->hasImage()) {
     QImage image = qvariant_cast<QImage>(event->mimeData()->imageData());
     ...
 }

See also setImageData() and hasImage().

void QMimeData::removeFormat ( const QString & mimeType )

Removes the data entry for mimeType in the object.

This function was introduced in Qt 4.4.

QVariant QMimeData::retrieveData ( const QString & mimeType, QVariant::Type type ) const   [virtual protected]

Returns a variant with the given type containing data for the MIME type specified by mimeType. If the object does not support the MIME type or variant type given, a null variant is returned instead.

This function is called by the general data() getter and by the convenience getters (text(), html(), urls(), imageData(), and colorData()). You can reimplement it if you want to store your data using a custom data structure (instead of a QByteArray, which is what setData() provides). You would then also need to reimplement hasFormat() and formats().

See also data().

void QMimeData::setColorData ( const QVariant & color )

Sets the color data in the object to the given color.

Colors correspond to the MIME type application/x-color.

See also colorData(), hasColor(), and setData().

void QMimeData::setData ( const QString & mimeType, const QByteArray & data )

Sets the data associated with the MIME type given by mimeType to the specified data.

For the most common types of data, you can call the higher-level functions setText(), setHtml(), setUrls(), setImageData(), and setColorData() instead.

Note that if you want to use a custom data type in an item view drag and drop operation, you must register it as a Qt meta type, using the Q_DECLARE_METATYPE() macro, and implement stream operators for it. The stream operators must then be registered with the qRegisterMetaTypeStreamOperators() function.

See also data(), hasFormat(), QMetaType, and qRegisterMetaTypeStreamOperators().

void QMimeData::setHtml ( const QString & html )

Sets html as the HTML (MIME type text/html) used to represent the data.

See also html(), hasHtml(), setText(), and setData().

void QMimeData::setImageData ( const QVariant & image )

Sets the data in the object to the given image.

A QVariant is used because QMimeData belongs to the QtCore library, whereas QImage belongs to QtGui. The conversion from QImage to QVariant is implicit. For example:

 mimeData->setImageData(QImage("beautifulfjord.png"));

See also imageData(), hasImage(), and setData().

void QMimeData::setText ( const QString & text )

Sets text as the plain text (MIME type text/plain) used to represent the data.

See also text(), hasText(), setHtml(), and setData().

void QMimeData::setUrls ( const QList<QUrl> & urls )

Sets the URLs stored in the MIME data object to those specified by urls.

URLs correspond to the MIME type text/uri-list.

See also urls(), hasUrls(), and setData().

QString QMimeData::text () const

Returns a plain text (MIME type text/plain) representation of the data.

See also setText(), hasText(), html(), and data().

QList<QUrl> QMimeData::urls () const

Returns a list of URLs contained within the MIME data object.

URLs correspond to the MIME type text/uri-list.

See also setUrls(), hasUrls(), and data().
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