org.eclipse.swt.widgets
Class Display

java.lang.Object
  org.eclipse.swt.graphics.Device
      org.eclipse.swt.widgets.Display

All Implemented Interfaces:

Adaptable

public class Display

extends Device

implements Adaptable

Instances of this class are responsible for managing the connection between SWT and the underlying operating system. Their most important function is to implement the SWT event loop in terms of the platform event model. They also provide various methods for accessing information about the operating system, and have overall control over the operating system resources which SWT allocates.

Applications which are built with SWT will almost always require only a single display. In particular, some platforms which SWT supports will not allow more than one active display. In other words, some platforms do not support creating a new display if one already exists that has not been sent the dispose() message.

In SWT, the thread which creates a Display instance is distinguished as the user-interface thread for that display.

The user-interface thread for a particular display has the following special attributes:

• The event loop for that display must be run from the thread.
• Some SWT API methods (notably, most of the public methods in Widget and its subclasses), may only be called from the thread. (To support multi-threaded user-interface applications, class Display provides inter-thread communication methods which allow threads other than the user-interface thread to request that it perform operations on their behalf.)
• The thread is not allowed to construct other Displays until that display has been disposed. (Note that, this is in addition to the restriction mentioned above concerning platform support for multiple displays. Thus, the only way to have multiple simultaneously active displays, even on platforms which support it, is to have multiple threads.)

Enforcing these attributes allows SWT to be implemented directly on the underlying operating system's event model. This has numerous benefits including smaller footprint, better use of resources, safer memory management, clearer program logic, better performance, and fewer overall operating system threads required. The down side however, is that care must be taken (only) when constructing multi-threaded applications to use the inter-thread communication mechanisms which this class provides when required.

All SWT API methods which may only be called from the user-interface thread are distinguished in their documentation by indicating that they throw the "ERROR_THREAD_INVALID_ACCESS" SWT exception.

Styles:

(none)

Events:

Close, Dispose

IMPORTANT: This class is not intended to be subclassed.

Since:

1.0

See Also:

syncExec(java.lang.Runnable), asyncExec(java.lang.Runnable), wake(), readAndDispatch(),

Constructor Summary

Display()
Constructs a new instance of this class.

Method Summary

void	addFilter(int eventType, Listener listener) Adds the listener to the collection of listeners who will be notified when an event of the given type occurs anywhere in a widget.
void	asyncExec(Runnable runnable) Causes the run() method of the runnable to be invoked by the user-interface thread at the next reasonable opportunity.
void	dispose()
Shell	getActiveShell() Returns the currently active Shell, or null if no shell belonging to the currently running application is active.
Object	getAdapter(Class adapter) Returns an object which is an instance of the given class parameter associated with this object or null if no association exists.
Rectangle	getBounds() Returns a rectangle describing the receiver's size and location.
static Display	getCurrent() Returns the display which the currently running thread is the user-interface thread for, or null if the currently running thread is not a user-interface thread for any display.
static Display	getDefault() Returns the default display.
int	getDoubleClickTime() Returns the longest duration, in milliseconds, between two mouse button clicks that will be considered a double click .
Control	getFocusControl() Returns the control which currently has keyboard focus, or null if keyboard events are not currently going to any of the controls built by the currently running application.
Shell[]	getShells() Returns a (possibly empty) array containing all shells which have not been disposed and have the receiver as their display.
Color	getSystemColor(int id) Returns the matching standard color for the given constant, which should be one of the color constants specified in class SWT.
Image	getSystemImage(int id) Returns the matching standard platform image for the given constant, which should be one of the icon constants specified in class SWT.
Thread	getThread() Returns the user-interface thread for the receiver.
boolean	isDisposed()
Point	map(Control from, Control to, int x, int y) Maps a point from one coordinate system to another.
Rectangle	map(Control from, Control to, int x, int y, int width, int height) Maps a point from one coordinate system to another.
Point	map(Control from, Control to, Point point) Maps a point from one coordinate system to another.
Rectangle	map(Control from, Control to, Rectangle rectangle) Maps a point from one coordinate system to another.
boolean	readAndDispatch() Reads an event from the event queue, dispatches it appropriately, and returns true if there is potentially more work to do, or false if the caller can sleep until another event is placed on the event queue.
void	removeFilter(int eventType, Listener listener) Removes the listener from the collection of listeners who will be notified when an event of the given type occurs anywhere in a widget.
void	sleep() Causes the user-interface thread to sleep (that is, to be put in a state where it does not consume CPU cycles) until an event is received or it is otherwise awakened.
void	syncExec(Runnable runnable) Causes the run() method of the runnable to be invoked by the user-interface thread at the next reasonable opportunity.
void	wake() Notifies the client side to send an life cycle request as UI thread to perform UI-updates.

Methods inherited from class org.eclipse.swt.graphics.Device

checkDevice, getSystemFont

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Display

public Display()

Constructs a new instance of this class.

Note: The resulting display is marked as the current display. If this is the first display which has been constructed since the application started, it is also marked as the default display.

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if called from a thread that already created an existing display
• ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass

See Also:

getCurrent(), getDefault(), Widget.checkSubclass(), Shell

Method Detail

getCurrent

public static Display getCurrent()

Returns the display which the currently running thread is the user-interface thread for, or null if the currently running thread is not a user-interface thread for any display.

Returns:

the current display

getDefault

public static Display getDefault()

Returns the default display. One is created (making the thread that invokes this method its user-interface thread) if it did not already exist.

RWT specific: This will not return a new display if there is none available. This may be fixed in the future.

Returns:

the default display

getBounds

public Rectangle getBounds()

Returns a rectangle describing the receiver's size and location.

Returns:

the bounding rectangle

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

getFocusControl

public Control getFocusControl()

Returns the control which currently has keyboard focus, or null if keyboard events are not currently going to any of the controls built by the currently running application.

Returns:

the control under the cursor

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

map

public Point map(Control from,
                 Control to,
                 Point point)

Maps a point from one coordinate system to another. When the control is null, coordinates are mapped to the display.

NOTE: On right-to-left platforms where the coordinate systems are mirrored, special care needs to be taken when mapping coordinates from one control to another to ensure the result is correctly mirrored. Mapping a point that is the origin of a rectangle and then adding the width and height is not equivalent to mapping the rectangle. When one control is mirrored and the other is not, adding the width and height to a point that was mapped causes the rectangle to extend in the wrong direction. Mapping the entire rectangle instead of just one point causes both the origin and the corner of the rectangle to be mapped.

Parameters:

from - the source Control or null

to - the destination Control or null

point - to be mapped

Returns:

point with mapped coordinates

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the point is null
• ERROR_INVALID_ARGUMENT - if the Control from or the Control to have been disposed

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

map

public Point map(Control from,
                 Control to,
                 int x,
                 int y)

Maps a point from one coordinate system to another. When the control is null, coordinates are mapped to the display.

NOTE: On right-to-left platforms where the coordinate systems are mirrored, special care needs to be taken when mapping coordinates from one control to another to ensure the result is correctly mirrored. Mapping a point that is the origin of a rectangle and then adding the width and height is not equivalent to mapping the rectangle. When one control is mirrored and the other is not, adding the width and height to a point that was mapped causes the rectangle to extend in the wrong direction. Mapping the entire rectangle instead of just one point causes both the origin and the corner of the rectangle to be mapped.

Parameters:

from - the source Control or null

to - the destination Control or null

x - coordinates to be mapped

y - coordinates to be mapped

Returns:

point with mapped coordinates

Throws:

IllegalArgumentException -

• ERROR_INVALID_ARGUMENT - if the Control from or the Control to have been disposed

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

map

public Rectangle map(Control from,
                     Control to,
                     Rectangle rectangle)

Maps a point from one coordinate system to another. When the control is null, coordinates are mapped to the display.

NOTE: On right-to-left platforms where the coordinate systems are mirrored, special care needs to be taken when mapping coordinates from one control to another to ensure the result is correctly mirrored. Mapping a point that is the origin of a rectangle and then adding the width and height is not equivalent to mapping the rectangle. When one control is mirrored and the other is not, adding the width and height to a point that was mapped causes the rectangle to extend in the wrong direction. Mapping the entire rectangle instead of just one point causes both the origin and the corner of the rectangle to be mapped.

Parameters:

from - the source Control or null

to - the destination Control or null

rectangle - to be mapped

Returns:

rectangle with mapped coordinates

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the rectangle is null
• ERROR_INVALID_ARGUMENT - if the Control from or the Control to have been disposed

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

map

public Rectangle map(Control from,
                     Control to,
                     int x,
                     int y,
                     int width,
                     int height)

Maps a point from one coordinate system to another. When the control is null, coordinates are mapped to the display.

NOTE: On right-to-left platforms where the coordinate systems are mirrored, special care needs to be taken when mapping coordinates from one control to another to ensure the result is correctly mirrored. Mapping a point that is the origin of a rectangle and then adding the width and height is not equivalent to mapping the rectangle. When one control is mirrored and the other is not, adding the width and height to a point that was mapped causes the rectangle to extend in the wrong direction. Mapping the entire rectangle instead of just one point causes both the origin and the corner of the rectangle to be mapped.

Parameters:

from - the source Control or null

to - the destination Control or null

x - coordinates to be mapped

y - coordinates to be mapped

width - coordinates to be mapped

height - coordinates to be mapped

Returns:

rectangle with mapped coordinates

Throws:

IllegalArgumentException -

• ERROR_INVALID_ARGUMENT - if the Control from or the Control to have been disposed

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

dispose

public void dispose()

isDisposed

public boolean isDisposed()

getAdapter

public Object getAdapter(Class adapter)

Description copied from interface: Adaptable

Returns an object which is an instance of the given class parameter associated with this object or null if no association exists.

Specified by:

getAdapter in interface Adaptable

Parameters:

adapter - the lookup class

Returns:

a object castable to the given class or null if there is no adapter associated with the given class.

getShells

public Shell[] getShells()

Returns a (possibly empty) array containing all shells which have not been disposed and have the receiver as their display.

Returns:

the receiver's shells

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

getActiveShell

public Shell getActiveShell()

Returns the currently active Shell, or null if no shell belonging to the currently running application is active.

Returns:

the active shell or null

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

getThread

public Thread getThread()

Returns the user-interface thread for the receiver. Note that the user-interface thread may change per user-request.

Returns:

the receiver's user-interface thread or null if there's no current user-request executed that belongs to the display.

Throws:

SWTException -

• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

asyncExec

public void asyncExec(Runnable runnable)

Causes the run() method of the runnable to be invoked by the user-interface thread at the next reasonable opportunity. Note that the user-interface thread may change per user-request. The caller of this method continues to run in parallel, and is not notified when the runnable has completed. Specifying null as the runnable simply wakes the user-interface thread when run.

Note that at the time the runnable is invoked, widgets that have the receiver as their display may have been disposed. Therefore, it is necessary to check for this case inside the runnable before accessing the widget.

Parameters:

runnable - code to run on the user-interface thread or null

Throws:

SWTException -

• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

See Also:

syncExec(java.lang.Runnable)

syncExec

public void syncExec(Runnable runnable)

Causes the run() method of the runnable to be invoked by the user-interface thread at the next reasonable opportunity. Note that the user-interface thread may change per user-request. The thread which calls this method is suspended until the runnable completes. Specifying null as the runnable simply wakes the user-interface thread.

Note that at the time the runnable is invoked, widgets that have the receiver as their display may have been disposed. Therefore, it is necessary to check for this case inside the runnable before accessing the widget.

Parameters:

runnable - code to run on the user-interface thread or null

Throws:

SWTException -

• ERROR_FAILED_EXEC - if an exception occured when executing the runnable
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

See Also:

asyncExec(java.lang.Runnable)

readAndDispatch

public boolean readAndDispatch()

Reads an event from the event queue, dispatches it appropriately, and returns true if there is potentially more work to do, or false if the caller can sleep until another event is placed on the event queue.

In addition to checking the system event queue, this method also checks if any inter-thread messages (created by syncExec() or asyncExec()) are waiting to be processed, and if so handles them before returning.

Returns:

false if the caller can sleep upon return from this method

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed
• ERROR_FAILED_EXEC - if an exception occurred while running an inter-thread message

Since:

1.1

See Also:

sleep(), wake()

sleep

public void sleep()

Causes the user-interface thread to sleep (that is, to be put in a state where it does not consume CPU cycles) until an event is received or it is otherwise awakened.

Returns:

true if an event requiring dispatching was placed on the queue.

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

Since:

1.1

See Also:

wake()

wake

public void wake()

Notifies the client side to send an life cycle request as UI thread to perform UI-updates. Note that this method may be called from any thread.

Note that this only works as expected if the UICallBack mechanism is activated.

Throws:

SWTException -

• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

getSystemColor

public Color getSystemColor(int id)

Returns the matching standard color for the given constant, which should be one of the color constants specified in class SWT. Any value other than one of the SWT color constants which is passed in will result in the color black. This color should not be free'd because it was allocated by the system, not the application.

Overrides:

getSystemColor in class Device

Parameters:

id - the color constant

Returns:

the matching color

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

See Also:

SWT

getSystemImage

public Image getSystemImage(int id)

Returns the matching standard platform image for the given constant, which should be one of the icon constants specified in class SWT. This image should not be free'd because it was allocated by the system, not the application. A value of null will be returned either if the supplied constant is not an SWT icon constant or if the platform does not define an image that corresponds to the constant.

Parameters:

id - the SWT icon constant

Returns:

the corresponding image or null

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

See Also:

SWT.ICON_ERROR, SWT.ICON_INFORMATION, SWT.ICON_QUESTION, SWT.ICON_WARNING, SWT.ICON_WORKING

getDoubleClickTime

public int getDoubleClickTime()

Returns the longest duration, in milliseconds, between two mouse button clicks that will be considered a double click .

Returns:

the double click time

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

Since:

1.2

addFilter

public void addFilter(int eventType,
                      Listener listener)

Adds the listener to the collection of listeners who will be notified when an event of the given type occurs anywhere in a widget. The event type is one of the event constants defined in class SWT. When the event does occur, the listener is notified by sending it the handleEvent() message.

Setting the type of an event to SWT.None from within the handleEvent() method can be used to change the event type and stop subsequent Java listeners from running. Because event filters run before other listeners, event filters can both block other listeners and set arbitrary fields within an event. For this reason, event filters are both powerful and dangerous. They should generally be avoided for performance, debugging and code maintenance reasons.

Parameters:

eventType - the type of event to listen for

listener - the listener which should be notified when the event occurs

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the listener is null

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
• ERROR_DEVICE_DISPOSED - if the receiver has been disposed

See Also:

Listener, SWT,

removeFilter

public void removeFilter(int eventType,
                         Listener listener)

Removes the listener from the collection of listeners who will be notified when an event of the given type occurs anywhere in a widget. The event type is one of the event constants defined in class SWT.

Parameters:

eventType - the type of event to listen for

listener - the listener which should no longer be notified when the event occurs

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the listener is null

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

Listener, SWT,