利用UIPickerView实现一个简单的点菜界面，如下图所示。源码地址：

UIPickerView有两个协议UIPickerViewDataSource,UIPickerViewDelegate，它们为UIPickeView提供数据和代理。UIPickeView的三个component分别代表fruit，main，drink，选中某一行，菜名在下面显示。最上面的随机按钮，则实现随机点菜功能。

1.viewController实现两个协议，并且引用相关数据和控件。

@interface CsyViewController () 
     
      @property (strong,nonatomic) NSArray *foodGroups;@property (weak, nonatomic) IBOutlet UIPickerView *picker;@property (weak, nonatomic) IBOutlet UILabel *fruitLabel;@property (weak, nonatomic) IBOutlet UILabel *mainLabel;@property (weak, nonatomic) IBOutlet UILabel *drinkLabel;@property (weak, nonatomic) IBOutlet UIButton *randBtn;@end
     

2.数据保存在plist文件中，由foodGroup引用，并且使用懒加载读取数据。

//重写getter方法，懒加载实现- (NSArray *)foodGroups{    if (!_foodGroups) {        NSString *path = [[NSBundle mainBundle] pathForResource:@"foods.plist" ofType:nil];                _foodGroups = [NSArray arrayWithContentsOfFile:path];    }        return _foodGroups;    }

3.UIPickerViewDataSource提供的相关信息：component数以及每个component有多少行

#pragma mark -- UIPickerViewDataSource//返回component数- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{    return self.foodGroups.count;}//返回每个component有多少行- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{    return [self.foodGroups[component] count];}

4.UIPickerViewDelegate提供每一行显示的数据。

#pragma mark -- UIPickerViewDelegate//每一行显示的数据，字符串数据- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{    return self.foodGroups[component][row];}

5.在UIPickerView选中某一行后，需要动态更改下方的菜名。这个是通过UIPickerViewDelegate协议的didSelectRow:方法实现的，当选中某一行，会自动调用该方法。即在该方法中动态地改变菜名。

- (void)viewDidLoad{    [super viewDidLoad];//    for (NSArray *group in self.foodGroups) {//        CsyLog(@"%@",group);//    }        //初始化三个label，菜单名    for (int i = 0; i < self.foodGroups.count; i++) {        [self pickerView:self.picker didSelectRow:4 inComponent:i];    }    //    NSInteger row = [self.picker selectedRowInComponent:0];//    CsyLog(@"selected row = %d",row);        //监听方法    [self.randBtn addTarget:self action:@selector(randBtnDidClick:) forControlEvents:UIControlEventTouchUpInside];        }#pragma mark --randBtn Listener- (void)randBtnDidClick:(UIButton *)button{//    CsyLog(@"click");        for (int i = 0; i < self.foodGroups.count; i++) {        NSArray *group = self.foodGroups[i];        NSInteger newRow = arc4random() % group.count;        //之前被选中的行        NSInteger currentRow = [self.picker selectedRowInComponent:i];//        NSLog(@"currentRow = %d",currentRow);        //如果随机值和当前的值相当，随机的值加1        if (newRow == currentRow) {            newRow = (newRow + 1) % group.count;        }//        NSLog(@"newRow = %d",newRow);        //选中某行某列        [self.picker selectRow:newRow inComponent:i animated:YES];        //调用didSecled方法,更新三个label        [self pickerView:self.picker didSelectRow:newRow inComponent:i];    }        }