直接上代碼：
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if([[UIDevice currentDevice] respondsToSelector:@selector(setOrientation:)]) {
SEL selector = NSSelectorFromString(@"setOrientation:");
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[UIDevice instanceMethodSignatureForSelector:selector]];
[invocation setSelector:selector];
[invocation setTarget:[UIDevice currentDevice]];
NSInteger val = UIInterfaceOrientationLandscapeLeft;//橫屏
[invocation setArgument:&val atIndex:2];
[invocation invoke];
}
}
