gWidgets-dnd: Functions to add drag and drop ability to widgets

Description

These functions allow drag and drop between widgets. The basic idea is that one creates drop sources from which one defines values which may be dragged and drop target where values may be dropped. These values can be text, or widgets.

Usage

adddropsource (obj, targetType = "text", handler = NULL, action = NULL, 
    ...) 
adddropmotion (obj, handler = NULL, action = NULL, ...) 
adddroptarget (obj, targetType = "text", handler = NULL, action = NULL, 
    ...)

Arguments

obj

Object to put drop handler on

targetType

What type of drop target: either "text" or "pixmap" or "entry".

handler

Handler called for the drop motion

action

action passed to handler

...

Not documented, currently has no role.

Value

These functions return an ID returned when registering a handler. The function removehandler uses this information to remove a drag and drop handler.

Details

To specify if one can drag values from a widget use adddropsource called on the object. The argument targetType can be set to "object" when the drop value is to be a widget, and not a string. The arguments handler and action can be used to describe what gets dropped. The default is to drop the widget's contents as returned by svalue.

To specify if an object is a drop target the adddroptarget method is called on the object. The argument handler (but no action) is used to handle the drop.

The handler's first argument is a list with named components. The obj component refers to the object that has the target placed on it. The component dropdata is set by the adddropsource method. The dropdata is typically a string, but a mechanism is in place to drop widgets. The default handler for adddroptarget is to replace the widget's value with the dropped data.

To add an action to a motion event, use the adddropmotion method. The adddroptarget must first have been added to the object.

Examples

Run this code

# NOT RUN {
## simple dnd
lab  = glabel("drag me",container=gwindow())
ed = gedit("drop here",container = gwindow())
adddropsource(lab)
adddroptarget(ed)
adddropmotion(ed,handler=function(h,...) print("bombs away"))

## more complicated
## this shows that rows of editable data frame can be dropped.
## by assigning to the changed signal, the graphs can be dynamic.
## THat is, drop a column, then edit it. The graph will update. The key
## is referring to the "value" stored in gd. This refers to the column
## in the editable data frame.
## By using svalue() and id(), the dropped value can also be a
## character string referring to a variable in the workspace.
adf = gdf(mtcars, container = gwindow())
gd = ggraphics(container = gwindow())
plotData = function() {
  dropvalue = tag(gd,"value")
  theValues = svalue(dropvalue)
  theName = id(dropvalue)
  hist(theValues, xlab=theName, main="")
}

ids = adddroptarget(gd,targetType="object", handler = function(h,...) {
    tag(gd, "value") <- h$dropdata
    plotData()

    if(is.gdataframecolumn(h$dropdata)) {
      view.col = h$dropdata
      id = addhandlerchanged(view.col, handler=function(h,...) plotData())
    }
})
# }