ExternalDropHandler
Last updated at 12:23 pm UTC on 13 January 2022
Instance variables are the same since Squeak 3.2
Squeak Squeak 3.10.2 to 5.3
Object subclass: #ExternalDropHandler
instanceVariableNames: 'action type extension'
classVariableNames: 'DefaultHandler RegisteredHandlers'
poolDictionaries: ''
category: 'System-Support'
Analysis: What happens if a file is dropped onto a Morphic desktop?
PasteUpMorph is the desktop
An instance of PasteUpMorph which answers
self isWorldMorph
as
true
is used as a desktop.
This is as well the answer of Project current world.
PasteUpMorph selectors select: [ :s | s asString includesSubstring: 'drop']
gives
#(#dropFiles: #dropEnabled)
So when a file is dropped onto the desktop the method #dropFiles: anEvent is called.
The method #dropFiles: then gets with the following method an instance of ExternalDropHandler
handleDroppedItem: anItem event: anEvent
(ExternalDropHandler lookupExternalDropHandler: anItem)
ifNotNil: [:handler | handler handle: anItem in: self dropEvent: anEvent].
to handle the dropped item.
ExternalDropHandler>>handleDroppedItem:event:
The class method
handleDroppedItem: anItem event: anEvent
is called by PasteUpMorph to find out about a handler to process the dropped file.
The code of the method ExternalDropHandler>>handleDroppedItem:event"
handleDroppedItem: anItem event: anEvent
(ExternalDropHandler lookupExternalDropHandler: anItem)
ifNotNil: [:handler | handler handle: anItem in: self dropEvent: anEvent].
There are internal drop handler (internal to the "ExternalDropHandler") and "external" drop handlers ("external" to the "ExternalDropHandler")
There are only two internal drop handlers (Squeak 6.0a) and more than 40 external ones (mangaged by FileServices).
Get drop handler from file services.
In most cases ExternalDropHandler lookupExternalDropHandler:
uses the method ExternalDropHandler lookupServiceBasedHandler:
to find out from FileServices registry about a service to process the dropped file.
lookupServiceBasedHandler: dropStream
"The file was just dropped; let's do our job"
| fileName services theOne |
fileName := dropStream name.
services := (FileServices itemsForFile: fileName)
reject: [:svc | self unwantedSelectors includes: svc selector].
"no service, default behavior"
services isEmpty
ifTrue: [^nil].
theOne := self chooseServiceFrom: services.
^theOne
ifNotNil: [ExternalDropHandler type: nil extension: nil action: [:stream | theOne performServiceFor: stream]].
Then ExternalDropHandler chooseServiceFrom:
chooseServiceFrom: aCollection
"private - choose a service from aCollection asking the user if needed"
^aCollection size = 1
ifTrue: [aCollection anyOne]
ifFalse:[UIManager default
chooseFrom: (aCollection collect:[:each| each label])
values: aCollection
title: 'You dropped a file. Please choose a service:' translated withCRs].
brings up the dialog box for the user to choose from. The dialog box below is shown after dropping a TrueType font file.
https://sequencediagram.org/
title Dropping a file onto the desktop
aPasteUpMorph->aPasteUpMorph: handleEvent:anEvent
aPasteUpMorph->aPasteUpMorph: handleDropFiles: anEvent
aPasteUpMorph->aPasteUpMorph: dropFiles: anEvent
aPasteUpMorph->aPasteUpMorph:handleDroppedItem: anItem event: anEvent
aPasteUpMorph->ExternalDropHandler: lookupExternalDropHandler: anItem
ExternalDropHandler->ExternalDropHandler:lookupServiceBasedHandler: dropStream
ExternalDropHandler->FileServices:itemsForFile: fileName
ExternalDropHandler->ExternalDropHandler:chooseServiceFrom:
ExternalDropHandler->UIManager:chooseFrom:values:title:
ExternalDropHandler->SimpleServiceEntry:performServiceFor: stream
col := AlignmentMorph newColumn.
col addMorphBack: (StringMorph contents: 'ExternalDropHandler class').
col addMorphBack: (StringMorph contents: 'lookupExternalDropHandler: stream').
col openInHand
lookupExternalDropHandler: stream
| types extension serviceHandler |
types := stream mimeTypes.
types ifNotNil: [
self registeredHandlers do: [:handler |
(handler matchesTypes: types)
ifTrue: [^handler]]].
extension := FileDirectory extensionFor: stream name.
self registeredHandlers do: [:handler |
(handler matchesExtension: extension)
ifTrue: [^handler]].
self halt.
serviceHandler := self lookupServiceBasedHandler: stream.
^serviceHandler
ifNil: [self defaultHandler]
lookupServiceBasedHandler: dropStream
"The file was just dropped; let's do our job"
| fileName services theOne |
fileName := dropStream name.
services := (FileServices itemsForFile: fileName)
reject: [:svc | self unwantedSelectors includes: svc selector].
"no service, default behavior"
services isEmpty
ifTrue: [^nil].
theOne := self chooseServiceFrom: services.
^theOne
ifNotNil: [ExternalDropHandler type: nil extension: nil action: [:stream | theOne performServiceFor: stream]]
col := AlignmentMorph newColumn.
col addMorphBack: (StringMorph contents: '= col := AlignmentMorph newColumn.
col addMorphBack: (StringMorph contents: 'FileServices class').
col addMorphBack: (StringMorph contents: 'itemsForFile: fileName').
col openInHand
See also SRE Execution Tracer
