以下是来自官方帮助页面的示例:
## a simple editor for matrix objects. Method $edit() changes some
## range of values; method $undo() undoes the last edit.
mEdit <- setRefClass("mEdit",
fields = list( data = "matrix",
edits = "list"),
methods = list(
edit = function(i, j, value) {
## the following string documents the edit method
'Replaces the range [i, j] of the
object by value.
'
backup <-
list(i, j, data[i,j])
data[i,j] <<- value
edits <<- c(edits, list(backup))
invisible(value)
},
undo = function() {
'Undoes the last edit() operation
and update the edits field accordingly.
'
prev <- edits
if(length(prev)) prev <- prev[[length(prev)]]
else stop("No more edits to undo")
edit(prev[[1]], prev[[2]], prev[[3]])
## trim the edits list
length(edits) <<- length(edits) - 2
invisible(prev)
},
show = function() {
'Method for automatically printing matrix editors'
cat("Reference matrix editor object of class",
classLabel(class(.self)), "n")
cat("Data: n")
methods::show(data)
cat("Undo list is of length", length(edits), "n")
}
))
mEdit$methods(
save = function(file) {
'Save the current object on the file
in R external object format.
'
base::save(.self, file = file)
}
)
mv <- setRefClass("matrixViewer",
fields = c("viewerDevice", "viewerFile"),
contains = "mEdit",
methods = list( view = function() {
dd <- dev.cur(); dev.set(viewerDevice)
devAskNewPage(FALSE)
matplot(data, main = paste("After",length(edits),"edits"))
dev.set(dd)},
edit = # invoke previous method, then replot
function(i, j, value) {
callSuper(i, j, value)
view()
}))
## initialize and finalize methods
mv$methods( initialize =
function(file = "./matrixView.pdf", ...) {
viewerFile <<- file
pdf(viewerFile)
viewerDevice <<- dev.cur()
dev.set(dev.prev())
callSuper(...)
},
finalize = function() {
dev.off(viewerDevice)
})
一切都像宣传的那样工作,但是如果我添加这样的东西:
mEdit$methods(
initialize = function(data) {
data <<- data
}
)
然后尝试加载类,R报错:
Loading testRefClass
Error in .Object$initialize(...) (from testRefClass.R#52) :
argument "data" is missing, with no default
data
不在...
参数中吗?为什么R说它不见了?
你可以给初始化方法中传递的参数默认值:
mEdit$methods(
initialize = function(data = matrix()) {
data <<- data
}
)
nn <- mEdit()
> nn
Reference matrix editor object of class "mEdit"
Data:
[,1]
[1,] NA
Undo list is of length 0
> nn <- mEdit(data = matrix(1:4, 2,2))
> nn
Reference matrix editor object of class "mEdit"
Data:
[,1] [,2]
[1,] 1 3
[2,] 2 4
Undo list is of length 0
应该处理好错误信息。
mv
继承自mEdit
,因此callSuper(...)
应该在其initialize
方法中调用:
> rr <- mv()
> rr
Reference matrix editor object of class "matrixViewer"
Data:
[,1]
[1,] NA
Undo list is of length 0
,我们可以看到实例化一个新的mv
导致mEdit
的initialize
方法通过callSuper(...)
被调用。
> rr <- mv(data = matrix(1:4, 2,2))
> rr
Reference matrix editor object of class "matrixViewer"
Data:
[,1] [,2]
[1,] 1 3
[2,] 2 4
Undo list is of length 0