NSIS制作安装包，如何检测并卸载已有版本

将如下代码追加到NSIS脚本的尾部即可。

Var UNINSTALL_PROG

Function .onInit
  ClearErrors
  ReadRegStr $UNINSTALL_PROG ${PRODUCT_UNINST_ROOT_KEY} ${PRODUCT_UNINST_KEY} "UninstallString"
  IfErrors  done
  
  MessageBox MB_YESNOCANCEL|MB_ICONQUESTION \
    "检测到本机已经安装了 ${PRODUCT_NAME}。\
    $\n$\n是否先卸载已安装的版本？" \
      /SD IDYES \
      IDYES uninstall \
      IDNO done
  Abort
  
uninstall:
  CreateDirectory C:\WINDOWS\temp
  CopyFiles $UNINSTALL_PROG  C:\WINDOWS\temp\uninst.exe

  ExecWait '"C:\WINDOWS\temp\uninst.exe" /S _?=C:\WINDOWS\temp' $0
  DetailPrint "uninst.exe returned $0"
  Delete "C:\WINDOWS\temp\uninst.exe"

done:
FunctionEnd