问题：
在AppDelegate::applicationWillEnterForeground()代码中显示了一个对话框，结果从后台切换会前台时，出现
call to OpenGL ES API with no current context (logged once per thread)错误。
解决：
Don't call it inAppDelegate::applicationWillEnterForeground. Because OpenGL context will be lost when enter to background. At this time OpenGL context may not be re-create by Android system. So,please do the operation after it is totally enter foreground.（摘自网络）
在AppDelegate::applicationWillEnterForeground中启动一个定时器，延时一段时间（0.1，具体时间可能需要使用不同手机测试，确定）再显示对话框，结果就可以。
参考：
