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juce::DragAndDropContainer Class Reference

## Detailed Description

Enables drag-and-drop behaviour for a component and all its sub-components.

For a component to be able to make or receive drag-and-drop events, one of its parent components must derive from this class. It's probably best for the top-level component to implement it.

Then to start a drag operation, any sub-component can just call the startDragging() method, and this object will take over, tracking the mouse and sending appropriate callbacks to any child components derived from DragAndDropTarget which the mouse moves over.

Note: If all that you need to do is to respond to files being drag-and-dropped from the operating system onto your component, you don't need any of these classes: you can do this simply by overriding FileDragAndDropTarget::filesDropped().

See also
  DragAndDropTarget

The documentation for this class was generated from the following file:

- juce_gui_basics/mouse/juce_DragAndDropContainer.h

Inheritance diagram for juce::DragAndDropContainer:

## Public Member Functions

| DragAndDropContainer ()
| Creates a DragAndDropContainer.
virtual | ~DragAndDropContainer ()
| Destructor.
void | startDragging (const var &sourceDescription, Component *sourceComponent, const ScaledImage &dragImage=ScaledImage(), bool allowDraggingToOtherJuceWindows=false, const Point< int > *imageOffsetFromMouse=nullptr, const MouseInputSource *inputSourceCausingDrag=nullptr)
| Begins a drag-and-drop operation.
void | startDragging (const var &sourceDescription, Component *sourceComponent, Image dragImage, bool allowDraggingToOtherJuceWindows=false, const Point< int > *imageOffsetFromMouse=nullptr, const MouseInputSource *inputSourceCausingDrag=nullptr)
bool | isDragAndDropActive () const
| Returns true if something is currently being dragged.
int | getNumCurrentDrags () const
| Returns the number of things currently being dragged.
var | getCurrentDragDescription () const
| Returns the description of the thing that's currently being dragged.
var | getDragDescriptionForIndex (int index) const
| Same as the getCurrentDragDescription() method but takes a touch index parameter.
void | setCurrentDragImage (const ScaledImage &newImage)
| If a drag is in progress, this allows the image being shown to be dynamically updated.
void | setCurrentDragImage (const Image &newImage)
void | setDragImageForIndex (int index, const ScaledImage &newImage)
| Same as the setCurrentDragImage() method but takes a touch index parameter.
void | setDragImageForIndex (int index, const Image &newImage)

## Static Public Member Functions

static DragAndDropContainer * | findParentDragContainerFor (Component *childComponent)
| Utility to find the DragAndDropContainer for a given Component.
static bool | performExternalDragDropOfFiles (const StringArray &files, bool canMoveFiles, Component *sourceComponent=nullptr, std::function< void()> callback=nullptr)
| This performs an asynchronous drag-and-drop of a set of files to some external application.
static bool | performExternalDragDropOfText (const String &text, Component *sourceComponent=nullptr, std::function< void()> callback=nullptr)
| This performs an asynchronous drag-and-drop of a block of text to some external application.

## Protected Member Functions

virtual bool | shouldDropFilesWhenDraggedExternally (const DragAndDropTarget::SourceDetails &sourceDetails, StringArray &files, bool &canMoveFiles)
| Override this if you want to be able to perform an external drag of a set of files when the user drags outside of this container component.
virtual bool | shouldDropTextWhenDraggedExternally (const DragAndDropTarget::SourceDetails &sourceDetails, String &text)
| Override this if you want to be able to perform an external drag of text when the user drags outside of this container component.
virtual void | dragOperationStarted (const DragAndDropTarget::SourceDetails &)
| Subclasses can override this to be told when a drag starts.
virtual void | dragOperationEnded (const DragAndDropTarget::SourceDetails &)
| Subclasses can override this to be told when a drag finishes.

## Constructors and Destructors

## DragAndDropContainer()

juce::DragAndDropContainer::DragAndDropContainer | ( |  | ) |

Creates a DragAndDropContainer.

The object that derives from this class must also be a Component.

Referenced by dragOperationEnded(), and findParentDragContainerFor().

## ~DragAndDropContainer()

virtual juce::DragAndDropContainer::~DragAndDropContainer | ( |  | ) |

virtual

Destructor.

## Member Functions

## startDragging() [1/2]

void juce::DragAndDropContainer::startDragging | ( | const var & | sourceDescription,
|  | Component * | sourceComponent,
|  | const ScaledImage & | dragImage = ScaledImage(),
|  | bool | allowDraggingToOtherJuceWindows = false,
|  | const Point< int > * | imageOffsetFromMouse = nullptr,
|  | const MouseInputSource * | inputSourceCausingDrag = nullptr )

Begins a drag-and-drop operation.

This starts a drag-and-drop operation - call it when the user drags the mouse in your drag-source component, and this object will track mouse movements until the user lets go of the mouse button, and will send appropriate messages to DragAndDropTarget objects that the mouse moves over.

findParentDragContainerFor() is a handy method to call to find the drag container to use for a component.

Parameters

  sourceDescription | a string or value to use as the description of the thing being dragged - this will be passed to the objects that might be dropped-onto so they can decide whether they want to handle it
  sourceComponent | the component that is being dragged
  dragImage | the image to drag around underneath the mouse. If this is a null image, a snapshot of the sourceComponent will be used instead.
  allowDraggingToOtherJuceWindows | if true, the dragged component will appear as a desktop window, and can be dragged to DragAndDropTargets that are the children of components other than this one.
  imageOffsetFromMouse | if an image has been passed-in, this specifies the offset at which the image should be drawn from the mouse. If it isn't specified, then the image will be centred around the mouse. If an image hasn't been passed-in, this will be ignored.

  inputSourceCausingDrag

  the mouse input source which started the drag. When calling from within a mouseDown or mouseDrag event, you can pass MouseEvent::source to this method. If this param is nullptr then JUCE will use the mouse input source which is currently dragging. If there are several dragging mouse input sources (which can often occur on mobile) then JUCE will use the mouseInputSource which is closest to the sourceComponent.

Referenced by startDragging().

## startDragging() [2/2]

void juce::DragAndDropContainer::startDragging | ( | const var & | sourceDescription,
|  | Component * | sourceComponent,
|  | Image | dragImage,
|  | bool | allowDraggingToOtherJuceWindows = false,
|  | const Point< int > * | imageOffsetFromMouse = nullptr,
|  | const MouseInputSource * | inputSourceCausingDrag = nullptr )

inline

References startDragging().

## isDragAndDropActive()

bool juce::DragAndDropContainer::isDragAndDropActive | ( |  | ) | const

Returns true if something is currently being dragged.

## getNumCurrentDrags()

int juce::DragAndDropContainer::getNumCurrentDrags | ( |  | ) | const

Returns the number of things currently being dragged.

## getCurrentDragDescription()

var juce::DragAndDropContainer::getCurrentDragDescription | ( |  | ) | const

Returns the description of the thing that's currently being dragged.

If nothing's being dragged, this will return a null var, otherwise it'll return the var that was passed into startDragging().

If you are using drag and drop in a multi-touch environment then you should use the getDragDescriptionForIndex() method instead which takes a touch index parameter.

See also
  startDragging, getDragDescriptionForIndex

## getDragDescriptionForIndex()

var juce::DragAndDropContainer::getDragDescriptionForIndex | ( | int | index | ) | const

Same as the getCurrentDragDescription() method but takes a touch index parameter.

See also
  getCurrentDragDescription

## setCurrentDragImage() [1/2]

void juce::DragAndDropContainer::setCurrentDragImage | ( | const ScaledImage & | newImage | ) |

If a drag is in progress, this allows the image being shown to be dynamically updated.

If you are using drag and drop in a multi-touch environment then you should use the setDragImageForIndex() method instead which takes a touch index parameter.

See also
  setDragImageForIndex

## setCurrentDragImage() [2/2]

void juce::DragAndDropContainer::setCurrentDragImage | ( | const Image & | newImage | ) |

inline

References setCurrentDragImage().

Referenced by setCurrentDragImage().

## setDragImageForIndex() [1/2]

void juce::DragAndDropContainer::setDragImageForIndex | ( | int | index,
|  | const ScaledImage & | newImage )

Same as the setCurrentDragImage() method but takes a touch index parameter.

See also
  setCurrentDragImage

## setDragImageForIndex() [2/2]

void juce::DragAndDropContainer::setDragImageForIndex | ( | int | index,
|  | const Image & | newImage )

inline

References setDragImageForIndex().

Referenced by setDragImageForIndex().

## findParentDragContainerFor()

DragAndDropContainer * juce::DragAndDropContainer::findParentDragContainerFor | ( | Component * | childComponent | ) |

static

Utility to find the DragAndDropContainer for a given Component.

This will search up this component's parent hierarchy looking for the first parent component which is a DragAndDropContainer.

It's useful when a component wants to call startDragging but doesn't know the DragAndDropContainer it should to use.

Obviously this may return nullptr if it doesn't find a suitable component.

References DragAndDropContainer().

## performExternalDragDropOfFiles()

bool juce::DragAndDropContainer::performExternalDragDropOfFiles | ( | const StringArray & | files,
|  | bool | canMoveFiles,
|  | Component * | sourceComponent = nullptr,
|  | std::function< void()> | callback = nullptr )

static

This performs an asynchronous drag-and-drop of a set of files to some external application.

You can call this function in response to a mouseDrag callback, and it will use a native operating system drag-and-drop operation to move or copy some files to another application.

Parameters

  files | a list of filenames to drag
  canMoveFiles | if true, the app that receives the files is allowed to move the files to a new location (if this is appropriate). If false, the receiver is expected to make a copy of them.
  sourceComponent | normally, JUCE will assume that the component under the mouse is the source component of the drag, but you can use this parameter to override this.
  callback | an optional completion callback that will be called when the operation has ended.

Returns
  true if the drag operation was successfully started, or false if it failed for some reason

See also
  performExternalDragDropOfText

## performExternalDragDropOfText()

bool juce::DragAndDropContainer::performExternalDragDropOfText | ( | const String & | text,
|  | Component * | sourceComponent = nullptr,
|  | std::function< void()> | callback = nullptr )

static

This performs an asynchronous drag-and-drop of a block of text to some external application.

You can call this function in response to a mouseDrag callback, and it will use a native operating system drag-and-drop operation to move or copy some text to another application.

Parameters

  text | the text to copy
  sourceComponent | Normally, JUCE will assume that the component under the mouse is the source component of the drag, but you can use this parameter to override this.
  callback | an optional completion callback that will be called when the operation has ended.

Returns
  true if the drag operation was successfully started, or false if it failed for some reason

See also
  performExternalDragDropOfFiles

## shouldDropFilesWhenDraggedExternally()

virtual bool juce::DragAndDropContainer::shouldDropFilesWhenDraggedExternally | ( | const DragAndDropTarget::SourceDetails & | sourceDetails,
|  | StringArray & | files,
|  | bool & | canMoveFiles )

protected virtual

Override this if you want to be able to perform an external drag of a set of files when the user drags outside of this container component.

This method will be called when a drag operation moves outside the JUCE window, and if you want it to then perform a file drag-and-drop, add the filenames you want to the array passed in, and return true.

Parameters

  sourceDetails | information about the source of the drag operation
  files | on return, the filenames you want to drag
  canMoveFiles | on return, true if it's ok for the receiver to move the files; false if it must make a copy of them (see the performExternalDragDropOfFiles() method)

See also
  performExternalDragDropOfFiles, shouldDropTextWhenDraggedExternally

## shouldDropTextWhenDraggedExternally()

virtual bool juce::DragAndDropContainer::shouldDropTextWhenDraggedExternally | ( | const DragAndDropTarget::SourceDetails & | sourceDetails,
|  | String & | text )

protected virtual

Override this if you want to be able to perform an external drag of text when the user drags outside of this container component.

This method will be called when a drag operation moves outside the JUCE window, and if you want it to then perform a text drag-and-drop, copy the text you want to be dragged into the argument provided and return true.

Parameters

  sourceDetails | information about the source of the drag operation
  text | on return, the text you want to drag

See also
  shouldDropFilesWhenDraggedExternally

## dragOperationStarted()

virtual void juce::DragAndDropContainer::dragOperationStarted | ( | const DragAndDropTarget::SourceDetails & |  | ) |

protected virtual

Subclasses can override this to be told when a drag starts.

## dragOperationEnded()

virtual void juce::DragAndDropContainer::dragOperationEnded | ( | const DragAndDropTarget::SourceDetails & |  | ) |

protected virtual

Subclasses can override this to be told when a drag finishes.

References DragAndDropContainer().

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