UI基础 - UIPickerView

■ 简言

1. 选取器 UIPickerView  是用来取代 PC 上面的下拉菜单，它是一个大大的滚轮，尺寸固定 320×216

2. 选取器可以有多个表盘，每个都可以作为一个组件使用：UIPickerView 和 UITableView 类似，也需要一个数据源，不过选取器不使用索引路径，而是用一个 NSinteger 值来标识每一行

■ 使用方式

1. 实现一个省份选择器

#import "ViewController.h"
@interface ViewController ()<UIPickerViewDataSource,UIPickerViewDelegate> // 遵守协议
@property(nonatomic,strong)UIPickerView *pickerView;
@property(nonatomic,strong)NSMutableArray *provincesArray; // 数据源：省份
@property(nonatomic,strong)NSMutableArray *cityArray;      // 数据源：省会
@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 数据源
    NSString *str = [[NSBundle mainBundle] pathForResource:@"Provineces" ofType:@"plist"];
    self.provincesArray= [NSMutableArray arrayWithContentsOfFile:str];
    
    // UIPickerView
    self.pickerView = [[UIPickerView alloc] initWithFrame:self.view.bounds];
    self.pickerView.delegate = self;
    self.pickerView.dataSource = self;
    self.pickerView.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:self.pickerView];
}

#pragma mark - <UIPickerViewDataSource>
// 组件个数
-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
    return 2;
}

// 组件行数
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{
    if (component == 0) {
        return self.provincesArray.count;
    }
    return self.cityArray.count;
}

#pragma mark - <UIPickerViewDelegate>
// 高
-(CGFloat) pickerView:(UIPickerView *)pickerView rowHeightForComponent: (NSInteger) component{
    return 25;
}

// 宽
-(CGFloat)pickerView: (UIPickerView *)pickerView widthForComponent:(NSInteger) component{
    return 95;
}

// 显示内容
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
    if (component == 0) {
        return [[self.provincesArray objectAtIndex:row] objectForKey:@"ProvinceName"];
    }
    return [[self.cityArray objectAtIndex:row] objectForKey:@"CityName"];
}

// 当选中组件时
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
    
    if (component == 0) {
        self.cityArray =[[self.provincesArray objectAtIndex:row ] objectForKey:@"cities"];
        [self.pickerView selectRow:0 inComponent:1 animated:YES];// 选中指定组件 1，从下标 0 显示
        [self.pickerView reloadComponent:1];// 刷新数据：指定组件
    }
}

// 当给指定的 component.row 指定 view 时，触发该方法，返回值为用作 row 内容的 view
- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view{
    
    UILabel *pickerLabel = (UILabel *) view;
    if (!pickerLabel) {
        pickerLabel = [[UILabel alloc] init];
        pickerLabel.adjustsFontSizeToFitWidth = YES;
        pickerLabel.textAlignment = NSTextAlignmentCenter;
        pickerLabel.layer.borderWidth = 3;
        pickerLabel.backgroundColor = [UIColor cyanColor];
        pickerLabel.font = [UIFont systemFontOfSize:15];
    }
    pickerLabel.text = [self pickerView:pickerView titleForRow:row forComponent:component];
    return pickerLabel;
}

@end

运行效果