简单的Objective C字符串操作

Question

我有以下格式的文件名

filename_ffffff.png
filename2_cccccc.png
...

如何操作此字符串并将其十六进制值替换为我选择的值.

说新的价值是fffccc什么,filename_ffffff.png并把它变成filename_fffccc.png

-(NSString *)replace:(NSString *)input with:(NSString *)newHex{
//find in input a patern of 6 char hex followed by dot png
// remove it from the string
// add the newHex followed by png
}

Answer 1

-(NSString *)replace:(NSString *)input with:(NSString *)newHex
{
    NSArray *seperated = [input componentsSeparatedByString:@"_"];
    return [NSString stringWithFormat:@"%@_%@.png", [seperated objectAtIndex:0], newHex];
}