r - R在Rgtk2程序中返回错误，说明“externalptr”不是子集

Question

我开始用 RGtk2 编写一个 R GUI，并且在我的代码的第三行收到错误

library(RGtk2)
window <- gtkWindow()
window["title"] <- "Testing"

错误是“externalptr”不是子集

> sessionInfo()
R version 2.12.2 (2011-02-25)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] RGtk2_2.20.19

loaded via a namespace (and not attached):
[1] tools_2.12.2