在iOS8以前，我们都习惯性用UIAlertView去做提示框，iOS8以后，苹果提倡使用UIAlertController取代UIAlertView。

#define SYSTEM_VERSION   [[UIDevice currentDevice].systemVersion floatValue]

if (SYSTEM_VERSION >= 8.0) {
                    UIAlertController *alertCtrl = [UIAlertController alertControllerWithTitle:@"赎回成功" message:nil preferredStyle:UIAlertControllerStyleAlert];
                    UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
                        [self.navigationController popViewControllerAnimated:YES];
                    }];
                    [alertCtrl addAction:okAction];
                    [self presentViewController:alertCtrl animated:YES completion:nil];
                    
                }else{
                //这个else一定要写，否则会导致在ios8一下的真机crash
                    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"赎回成功" message:nil delegate:self cancelButtonTitle:nil otherButtonTitles:@"确定", nil];
                    alert.tag = 998;
                    [alert show];
                }

#pragma mark-UIAlertViewDelegate
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (alertView.tag == 998) {
        [self.navigationController popViewControllerAnimated:YES];
    }
}