了解 UIPickerView 的工作原理

Question

相当新，我需要了解 UIPickerViews。

我以编程方式为我的项目创建了一个 UIPickerView：

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    UIPickerView *myPickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0, 200, 375, 200)];
    myPickerView.delegate = self;
    myPickerView.showsSelectionIndicator = YES;
    [self.view addSubview:myPickerView];   
}

然后添加了行数的方法：

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
    NSUInteger numRows = 5;

    return numRows;
}

按预期返回五个问号。然后我可以继续创建一个数组来填充这些行等......但接下来我会添加另一个 UIPickerView，如下所示：

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    UIPickerView *myPickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0, 200, 375, 200)];
    myPickerView.delegate = self;
    myPickerView.showsSelectionIndicator = YES;
    [self.view addSubview:myPickerView];

    UIPickerView *my2PickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0, 400, 375, 200)];
    my2PickerView.delegate = self;
    my2PickerView.showsSelectionIndicator = YES;
    [self.view addSubview:my2PickerView];
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
    NSUInteger numRows = 5;

    return numRows;
}

现在我有两个pickerview 控制器，它们都有五行。我的问题是如何选择该方法适用于哪个pickerview，还有谁能解释为什么该方法适用于项目中的所有pickerview？谢谢。

Answer 1

两个 PickerViews 只有一个委托方法；这是我不喜欢 iOS 的东西，但你在这里没有选择。

你必须if-statement自己摆脱这个。

委托方法中的pickerView参数是被分配行数的pickerview。

请注意，这对于 iOS 的任何常用委托方法都有效，无论是您的pickerview、tableview、collectionView 的numberOfRows，还是任何具有view in 参数的委托方法。

简单易懂的方法是将您的选择器视图作为您的类（或属性）的字段，然后简单地与它比较参数。

@interface ViewController ()
@property (weak, nonatomic) UIPickerView *_mySexyPickerView;
@property (weak, nonatomic) UIPickerView *_myOtherPickerView;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    _mySexyPickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0, 200, 375, 200)];
    _mySexyPickerView.delegate = self;
    _mySexyPickerView.showsSelectionIndicator = YES;
    [self.view addSubview:_mySexyPickerView];

    _myOtherPickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0, 400, 375, 200)];
    _myOtherPickerView.delegate = self;
    _myOtherPickerView.showsSelectionIndicator = YES;
    [self.view addSubview:_myOtherPickerView];
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
    if (pickerView == _mySexyPickerView){
         return 2;
    }

    if (pickerView == _myOtherPickerView){
         return 19;
    }
    return 0;
}