Cannot open include file: 'QWidget': No such file or directory

Solution: (vs2008 in)

1、"C/C++" -> "General" ->"Additional Include Directories"中，加入   ;"$(QTDIR)\include\QtNetwork"。

2, debug follows:

     “Linker” -> "Input"-> "Additional Dependencies"中，加入 QtNetworkd4.lib

     release follows:

      “Linker” -> "Input"-> "Additional Dependencies"中，加入 QtNetwork4.lib

or:

1, the #include <QNetworkAccessManager> to #include <QtNetwork / QNetworkAccessManager>

2, debug follows:

     “Linker” -> "Input"-> "Additional Dependencies"中，加入 QtNetworkd4.lib

     release follows:

      “Linker” -> "Input"-> "Additional Dependencies"中，加入 QtNetwork4.lib

Compiled it.