gistfile1.m

-(NSArray *)loadPadNibNamed:(NSString *)name owner:(id)owner options:(NSDictionary *)options {
    NSString *newName = [name stringByReplacingOccurrencesOfString:@"@pad" withString:@""];
    newName = [newName stringByAppendingFormat:@"@pad"];

    //判断是否存在
    NSFileManager *fm = [NSFileManager defaultManager];
    NSString* filepath = [[NSBundle mainBundle] pathForResource:newName ofType:@"nib"];

    //这里调用的loadPadNibNamed:owner:options:实际为为交换后的方法，即loadNibNamed:owner:options:
    if ([fm fileExistsAtPath:filepath]) {
        return [self loadPadNibNamed:newName owner:owner options:options];
    } else {
        return [self loadPadNibNamed:name owner:owner options:options]; 
    }
}