- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component {
    NSString *ret = @"";
    // ret = 你某一行显示的内容
    return ret;
}

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
        //选择某一行后的行动
}

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
    NSInteger ret = 0;  
    // 总共的列数
    return ret;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
         NSInteger ret = 0;
         //某一列的行数
         return ret;
}