使用NSPredicate过滤NSArray

有一个NSArray，我想用predicate过滤一下。

NSLog(@"text is %@",txtSearch.text);
NSPredicate *bPredicate =
[NSPredicate predicateWithFormat:@"SELF beginswith[c] '%@'",txtSearch.text];
arrSearchedPlayers =
[arrPlayers filteredArrayUsingPredicate:bPredicate];
NSLog(@"array after searched is %@",arrSearchedPlayers);

但是再输入文本时数组还是空的，使用下面的predicate的话就结果正常：

 NSPredicate *bPredicate =
    [NSPredicate predicateWithFormat:@"SELF beginswith[c] 's'"];

这是为什么呢？

NSPredicate *bPredicate =[NSPredicate predicateWithFormat:@"SELF beginswith[cd] %@",txtSearch.text];