UISearchBar 搜索框
UISearchBar *searchBar = [[UISearchBar alloc] initWithFrame:CGRectMake(0, 0, 320, 50)];
searchBar.placeholder=@"关键字";
searchBar.showsCancelButton = YES;
searchBar.barStyle = UIBarStyleBlack;
// searchBar.keyboardType=UIKeyboardTypeDefault;
// [searchBar resignFirstResponder]; //可以清空搜索框
searchBar.delegate = self;
[self addSubview:searchBar];