NSIS安装时自动卸载老版本

Section "" SecUninstallPrevious

    Call UninstallPrevious

SectionEnd

Function UninstallPrevious

    ; Check for uninstaller.
    ReadRegStr $R0 HKLM "${PRODUCT_UNINST_KEY}" "InstallDir"

    ${If} $R0 == ""       
        Goto Done
    ${EndIf}

    DetailPrint "Removing previous installation."   

    ; Run the uninstaller silently.
    ExecWait '"$R0\Uninstall.exe /S"'

    Done:

FunctionEnd