Class TransferHandler
- All Implemented Interfaces:
Serializable
Transferable
to and from Swing components. The Transferable is used to
represent data that is exchanged via a cut, copy, or paste
to/from a clipboard. It is also used in drag-and-drop operations
to represent a drag from a component, and a drop to a component.
Swing provides functionality that automatically supports cut, copy,
and paste keyboard bindings that use the functionality provided by
an implementation of this class. Swing also provides functionality
that automatically supports drag and drop that uses the functionality
provided by an implementation of this class. The Swing developer can
concentrate on specifying the semantics of a transfer primarily by setting
the transferHandler property on a Swing component.
This class is implemented to provide a default behavior of transferring
a component property simply by specifying the name of the property in
the constructor. For example, to transfer the foreground color from
one component to another either via the clipboard or a drag and drop operation
a TransferHandler can be constructed with the string "foreground". The
built in support will use the color returned by getForeground as the source
of the transfer, and setForeground for the target of a transfer.
Please see How to Use Drag and Drop and Data Transfer, a section in The Java Tutorial, for more information.
- Since:
- 1.4
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic classRepresents a location where dropped data should be inserted.static final classThis class encapsulates all relevant details of a clipboard or drag and drop transfer, and also allows for customizing aspects of the drag and drop experience. -
Field Summary
FieldsModifier and TypeFieldDescriptionstatic final intAnintrepresenting a "copy" transfer action.static final intAnintrepresenting a source action capability of either "copy" or "move".static final intAnintrepresenting a "link" transfer action.static final intAnintrepresenting a "move" transfer action.static final intAnintrepresenting no transfer action. -
Constructor Summary
ConstructorsModifierConstructorDescriptionprotectedConvenience constructor for subclasses.TransferHandler(String property) Constructs a transfer handler that can transfer a Java Bean property from one component to another via the clipboard or a drag and drop operation. -
Method Summary
Modifier and TypeMethodDescriptionbooleancanImport(JComponent comp, DataFlavor[] transferFlavors) Indicates whether a component will accept an import of the given set of data flavors prior to actually attempting to import it.booleancanImport(TransferHandler.TransferSupport support) This method is called repeatedly during a drag and drop operation to allow the developer to configure properties of, and to return the acceptability of transfers; with a return value oftrueindicating that the transfer represented by the givenTransferSupport(which contains all of the details of the transfer) is acceptable at the current time, and a value offalserejecting the transfer.protected TransferableCreates aTransferableto use as the source for a data transfer.voidexportAsDrag(JComponent comp, InputEvent e, int action) Causes the Swing drag support to be initiated.protected voidexportDone(JComponent source, Transferable data, int action) Invoked after data has been exported.voidexportToClipboard(JComponent comp, Clipboard clip, int action) Causes a transfer from the given component to the given clipboard.static ActionReturns anActionthat performs copy operations to the clipboard.static ActionReturns anActionthat performs cut operations to the clipboard.Returns the drag image.Returns an anchor offset for the image to drag.static ActionReturns anActionthat performs paste operations from the clipboard.intReturns the type of transfer actions supported by the source; any bitwise-OR combination ofCOPY,MOVEandLINK.Returns an object that establishes the look of a transfer.booleanimportData(JComponent comp, Transferable t) Causes a transfer to a component from a clipboard or a DND drop operation.booleanCauses a transfer to occur from a clipboard or a drag and drop operation.voidsetDragImage(Image img) Sets the drag image parameter.voidSets an anchor offset for the image to drag.
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Field Details
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NONE
public static final int NONEAnintrepresenting no transfer action.- See Also:
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COPY
public static final int COPYAnintrepresenting a "copy" transfer action. This value is used when data is copied to a clipboard or copied elsewhere in a drag and drop operation.- See Also:
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MOVE
public static final int MOVEAnintrepresenting a "move" transfer action. This value is used when data is moved to a clipboard (i.e. a cut) or moved elsewhere in a drag and drop operation.- See Also:
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COPY_OR_MOVE
public static final int COPY_OR_MOVEAnintrepresenting a source action capability of either "copy" or "move".- See Also:
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LINK
public static final int LINKAnintrepresenting a "link" transfer action. This value is used to specify that data should be linked in a drag and drop operation.- Since:
- 1.6
- See Also:
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Constructor Details
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TransferHandler
Constructs a transfer handler that can transfer a Java Bean property from one component to another via the clipboard or a drag and drop operation.- Parameters:
property- the name of the property to transfer; this can benullif there is no property associated with the transfer handler (a subclass that performs some other kind of transfer, for example)
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TransferHandler
protected TransferHandler()Convenience constructor for subclasses.
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Method Details
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getCutAction
Returns anActionthat performs cut operations to the clipboard. When performed, this action operates on theJComponentsource of theActionEventby invokingexportToClipboard, with aMOVEaction, on the component'sTransferHandler.- Returns:
- an
Actionfor performing cuts to the clipboard
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getCopyAction
Returns anActionthat performs copy operations to the clipboard. When performed, this action operates on theJComponentsource of theActionEventby invokingexportToClipboard, with aCOPYaction, on the component'sTransferHandler.- Returns:
- an
Actionfor performing copies to the clipboard
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getPasteAction
Returns anActionthat performs paste operations from the clipboard. When performed, this action operates on theJComponentsource of theActionEventby invokingimportData, with the clipboard contents, on the component'sTransferHandler.- Returns:
- an
Actionfor performing pastes from the clipboard
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setDragImage
Sets the drag image parameter. The image has to be prepared for rendering by the moment of the call. The image is stored by reference because of some performance reasons.- Parameters:
img- an image to drag
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getDragImage
Returns the drag image. If there is no image to drag, the returned value isnull.- Returns:
- the reference to the drag image
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setDragImageOffset
Sets an anchor offset for the image to drag. It can not benull.- Parameters:
p- aPointobject that corresponds to coordinates of an anchor offset of the image relative to the upper left corner of the image
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getDragImageOffset
Returns an anchor offset for the image to drag.- Returns:
- a
Pointobject that corresponds to coordinates of an anchor offset of the image relative to the upper left corner of the image. The point(0,0)returns by default.
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exportAsDrag
Causes the Swing drag support to be initiated. This is called by the various UI implementations in thejavax.swing.plaf.basicpackage if the dragEnabled property is set on the component. This can be called by custom UI implementations to use the Swing drag support. This method can also be called by a Swing extension written as a subclass ofJComponentto take advantage of the Swing drag support.The transfer will not necessarily have been completed at the return of this call (i.e. the call does not block waiting for the drop). The transfer will take place through the Swing implementation of the
java.awt.dndmechanism, requiring no further effort from the developer. TheexportDonemethod will be called when the transfer has completed.- Parameters:
comp- the component holding the data to be transferred; provided to enable sharing ofTransferHandlerse- the event that triggered the transferaction- the transfer action initially requested; eitherCOPY,MOVEorLINK; the DnD system may change the action used during the course of the drag operation
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exportToClipboard
public void exportToClipboard(JComponent comp, Clipboard clip, int action) throws IllegalStateException Causes a transfer from the given component to the given clipboard. This method is called by the default cut and copy actions registered in a component's action map.The transfer will take place using the
java.awt.datatransfermechanism, requiring no further effort from the developer. Any data transfer will be complete and theexportDonemethod will be called with the action that occurred, before this method returns. Should the clipboard be unavailable when attempting to place data on it, theIllegalStateExceptionthrown byClipboard.setContents(Transferable, ClipboardOwner)will be propagated through this method. However,exportDonewill first be called with an action ofNONEfor consistency.- Parameters:
comp- the component holding the data to be transferred; provided to enable sharing ofTransferHandlersclip- the clipboard to transfer the data intoaction- the transfer action requested; this should be a value of eitherCOPYorMOVE; the operation performed is the intersection of the transfer capabilities given by getSourceActions and the requested action; the intersection may result in an action ofNONEif the requested action isn't supported- Throws:
IllegalStateException- if the clipboard is currently unavailable- See Also:
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importData
Causes a transfer to occur from a clipboard or a drag and drop operation. TheTransferableto be imported and the component to transfer to are contained within theTransferSupport.While the drag and drop implementation calls
canImportto determine the suitability of a transfer before calling this method, the implementation of paste does not. As such, it cannot be assumed that the transfer is acceptable upon a call to this method for paste. It is recommended thatcanImportbe explicitly called to cover this case.Note: The
TransferSupportobject passed to this method is only valid for the duration of the method call. It is undefined what values it may contain after this method returns.- Parameters:
support- the object containing the details of the transfer, notnull.- Returns:
- true if the data was inserted into the component, false otherwise
- Throws:
NullPointerException- ifsupportisnull- Since:
- 1.6
- See Also:
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importData
Causes a transfer to a component from a clipboard or a DND drop operation. TheTransferablerepresents the data to be imported into the component.Note: Swing now calls the newer version of
importDatathat takes aTransferSupport, which in turn calls this method (if the component in theTransferSupportis aJComponent). Developers are encouraged to call and override the newer version as it provides more information (and is the only version that supports use with aTransferHandlerset directly on aJFrameor other non-JComponent).- Parameters:
comp- the component to receive the transfer; provided to enable sharing ofTransferHandlerst- the data to import- Returns:
- true if the data was inserted into the component, false otherwise
- See Also:
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canImport
This method is called repeatedly during a drag and drop operation to allow the developer to configure properties of, and to return the acceptability of transfers; with a return value oftrueindicating that the transfer represented by the givenTransferSupport(which contains all of the details of the transfer) is acceptable at the current time, and a value offalserejecting the transfer.For those components that automatically display a drop location during drag and drop, accepting the transfer, by default, tells them to show the drop location. This can be changed by calling
setShowDropLocationon theTransferSupport.By default, when the transfer is accepted, the chosen drop action is that picked by the user via their drag gesture. The developer can override this and choose a different action, from the supported source actions, by calling
setDropActionon theTransferSupport.On every call to
canImport, theTransferSupportcontains fresh state. As such, any properties set on it must be set on every call. Upon a drop,canImportis called one final time before calling intoimportData. Any state set on theTransferSupportduring that last call will be available inimportData.This method is not called internally in response to paste operations. As such, it is recommended that implementations of
importDataexplicitly call this method for such cases and that this method be prepared to return the suitability of paste operations as well.Note: The
TransferSupportobject passed to this method is only valid for the duration of the method call. It is undefined what values it may contain after this method returns.- Parameters:
support- the object containing the details of the transfer, notnull.- Returns:
trueif the import can happen,falseotherwise- Throws:
NullPointerException- ifsupportisnull- Since:
- 1.6
- See Also:
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canImport
Indicates whether a component will accept an import of the given set of data flavors prior to actually attempting to import it.Note: Swing now calls the newer version of
canImportthat takes aTransferSupport, which in turn calls this method (only if the component in theTransferSupportis aJComponent). Developers are encouraged to call and override the newer version as it provides more information (and is the only version that supports use with aTransferHandlerset directly on aJFrameor other non-JComponent).- Parameters:
comp- the component to receive the transfer; provided to enable sharing ofTransferHandlerstransferFlavors- the data formats available- Returns:
- true if the data can be inserted into the component, false otherwise
- See Also:
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getSourceActions
Returns the type of transfer actions supported by the source; any bitwise-OR combination ofCOPY,MOVEandLINK.Some models are not mutable, so a transfer operation of
MOVEshould not be advertised in that case. ReturningNONEdisables transfers from the component.- Parameters:
c- the component holding the data to be transferred; provided to enable sharing ofTransferHandlers- Returns:
COPYif the transfer property can be found, otherwise returnsNONE
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getVisualRepresentation
Returns an object that establishes the look of a transfer. This is useful for both providing feedback while performing a drag operation and for representing the transfer in a clipboard implementation that has a visual appearance. The implementation of theIconinterface should not alter the graphics clip or alpha level. The icon implementation need not be rectangular or paint all of the bounding rectangle and logic that calls the icons paint method should not assume the all bits are painted.nullis a valid return value for this method and indicates there is no visual representation provided. In that case, the calling logic is free to represent the transferable however it wants.The default Swing logic will not do an alpha blended drag animation if the return is
null.- Parameters:
t- the data to be transferred; this value is expected to have been created by thecreateTransferablemethod- Returns:
null, indicating there is no default visual representation
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createTransferable
Creates aTransferableto use as the source for a data transfer. Returns the representation of the data to be transferred, ornullif the component's property isnull- Parameters:
c- the component holding the data to be transferred; provided to enable sharing ofTransferHandlers- Returns:
- the representation of the data to be transferred, or
nullif the property associated withcisnull
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exportDone
Invoked after data has been exported. This method should remove the data that was transferred if the action wasMOVE.This method is implemented to do nothing since
MOVEis not a supported action of this implementation (getSourceActionsdoes not includeMOVE).- Parameters:
source- the component that was the source of the datadata- The data that was transferred or possibly null if the action isNONE.action- the actual action that was performed
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