UIPickerView滚轮选择器视图

//必须实现两个协议 
//数据源协议必须实现的两个方法
//选取器的输出借口singlePicker,并在故事版中选择该选取器将dataSource和delegate拖入视图控制器与之关联
//@property (weak, nonatomic) IBOutlet UIPickerView *singlePicker;
//characterNames是自己定义的属性数组，用于往选取器中添加显示数据
//@property (strong, nonatomic) NSArray *characterNames;
//选取器显示几个滚轮，返回1，显示1个
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
    return 1;
}

//选取器滚轮包含多少行，返回数组对象中的数量
- (NSInteger)pickerView:(UIPickerView *)pickerView
numberOfRowsInComponent:(NSInteger)component {

    return [self.characterNames count];
}

//委托协议,实现可选方法
//使用row参数作为索引,返回数组中相应的元素
- (NSString *)pickerView:(UIPickerView *)pickerView
             titleForRow:(NSInteger)row
            forComponent:(NSInteger)component {
    
    return self.characterNames[row];
}

//点击按钮触发事件，弹出警告框显示在选取器中选择的内容
- (IBAction)buttonPressed:(id)sender {
    //选取器组成部分0代表第一个选取器，1则代表第二个选取器，以此类推，赋值给一个整型对象 row
    NSInteger row = [self.singlePicker selectedRowInComponent:0];
    //获取数组中的内容并赋值给字符串对象selected
    NSString *selected = self.characterNames[row];
    NSString *title = [NSString stringWithFormat:@"You selected %@",selected];
    
    UIAlertController *singleAlert = [UIAlertController alertControllerWithTitle:title message:@"thank you for choosing" preferredStyle:UIAlertControllerStyleAlert];
    
    UIAlertAction *singleAction = [UIAlertAction actionWithTitle:@"Yes I did" style:UIAlertActionStyleDefault handler:nil];
    
    [singleAlert addAction:singleAction];
    
    [self presentViewController:singleAlert animated:YES completion:nil];