UIPickerView 显示但不加载数据

Question

我是 objective c 的新手。我已经查看了大量关于堆栈溢出的问题，试图找到答案，但没有任何帮助，所以我感谢任何人可以提供的帮助。

我正在尝试制作一个应用程序，该应用程序将从我的 51 个数字数组中加载选取器视图。将从数组中生成一个随机对象，如果用户从选择器中选择该对象，将显示一个警报。我打算做一个简单的小猜谜游戏，但现在我只有加载的选择器，但它是空白的，没有文本。警报确实有效。

我已经将数据源和委托分配给视图控制器上的选取器视图。

我需要帮助来弄清楚为什么我的选择器视图没有加载我的数组，以及我可以做些什么来修复它。谢谢

这是我的 h 文件：

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>

@property (strong, nonatomic) IBOutlet UIPickerView *picker;

@end

这里是 m 文件：

#import "ViewController.h"

@interface ViewController ()

@property NSArray *numbers;
@property NSString * selection;
@property NSString *randomObject;
@property NSInteger rnd;


@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor darkGrayColor];

     [_numbers arrayByAddingObjectsFromArray:_numbers];

}

-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
    return 1;
}

-(NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:      (NSInteger)component{
    return _numbers.count;
}

 -(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row    inComponent:(NSInteger)component{

    _numbers = @[@0,@1,@2,@3,@4,@5,@6,@7,@8,@9,@10,@11,@12,@13,@14,@15,@16,@17,@18,@19,@20,@21,@22,@23,@24,@25,@26,@27,@28,@29,@30,@31,@32,@33,@34,@35,@36,@37,@38,@39,@40,@41,@42,@43,@44,@45,@46,@47,@48,@49,@50];

    //create random object from array
_rnd = arc4random() % ([_numbers count]);

_selection = [NSString stringWithFormat:@"%ld",(long)row];
_randomObject = [_numbers objectAtIndex:self.rnd];
NSLog(@"%@",self.randomObject);


    //strings for alerts
NSString *right = [[NSString alloc]initWithFormat:@"You Guessed Right! Congratulations you've earned 3 points!"];
NSString *oneOff = [[NSString alloc]initWithFormat:@"You were so close! Only 1 off! The number was %lu. Congratulations you've earned 2 points!",(unsigned long)self.rnd];
NSString *twoOff = [[NSString alloc]initWithFormat:@"You were so close! Only 2 off! The number was %lu. Congratulations you've earned 1 point!",(unsigned long)self.rnd];
NSString *threeOff = [[NSString alloc]initWithFormat:@"Nice try! You were 3 off. The number was %lu. You earned -1 point.",(unsigned long)self.rnd];
NSString *fourOff = [[NSString alloc]initWithFormat:@"Good try! You were 2 off. The number was %lu. You earned -2 points.",(unsigned long)self.rnd];
NSString *fiveOff = [[NSString alloc]initWithFormat:@"You were no where close! The number was %lu. You earned -3 points!",(unsigned long)self.rnd];

    //alerts for guesses
UIAlertView *rightAlert = [[UIAlertView alloc]initWithTitle:@"Spot On!" message:right delegate:nil cancelButtonTitle:@"Sweet!" otherButtonTitles:nil, nil];
UIAlertView *oneOffAlert = [[UIAlertView alloc]initWithTitle:@"Only one off!" message:oneOff delegate:nil cancelButtonTitle:@"Ok!" otherButtonTitles:nil, nil];
UIAlertView *twoOffAlert = [[UIAlertView alloc]initWithTitle:@"Only Two Off!" message:twoOff delegate:nil cancelButtonTitle:@"Ok!" otherButtonTitles:nil, nil];
UIAlertView *threeOffAlert = [[UIAlertView alloc]initWithTitle:@"Three Off" message:threeOff delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil];
UIAlertView *fourOffAlert = [[UIAlertView alloc]initWithTitle:@"Four Off" message:fourOff delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil];
UIAlertView *fiveOffAlert = [[UIAlertView alloc]initWithTitle:@"No Where Close!" message:fiveOff delegate:nil cancelButtonTitle:@"Ok!" otherButtonTitles:nil, nil];


NSInteger a = [_selection integerValue];


    //guessed right
if (_selection == _randomObject)
{
    [rightAlert show];

}
    //one off
if (a == (_rnd + 1) || (a == (_rnd - 1)))
{
    [oneOffAlert show];

}
    //two off
if (a == (_rnd + 2) || (a == (_rnd - 2)))
{
    [twoOffAlert show];

}
    //three off
if (a == (_rnd + 3) || (a == (_rnd - 3)))
{
    [threeOffAlert show];

}
    //four off
if (a == (_rnd + 4) || (a == (_rnd - 4)))
{
    [fourOffAlert show];

}
    //five or more off
if ((_rnd + 5) >= a || (_rnd - 5) <= a ||(_rnd - 5) >= a || (_rnd + 5) <= a)
{
    [fiveOffAlert show];

}
}

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
return _numbers[row];
}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end

Answer 1

问题是这一行

_numbers = @[@0,@1,@2,@3,@4,@5,@6,@7,@8,@9,@10,@11,@12,@13,@14,@15,@16,@17,@18,@19,@20,@21,@22,@23,@24,@25,@26,@27,@28,@29,@30,@31,@32,@33,@34,@35,@36,@37,@38,@39,@40,@41,@42,@43,@44,@45,@46,@47,@48,@49,@50];

出现在错误的地方。它位于 pickerView:didSelectRow:inComponent: 方法中，仅在用户做出选择后调用。因此，您的 _numbers 数组将始终为空。

将其移至 viewDidLoad 方法，替换以下目前完全没有任何作用的语句：

[_numbers arrayByAddingObjectsFromArray:_numbers];

此外，您需要更改此方法：

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
   return [_numbers[row] stringValue];
}

因为 _numbers[row] 是 NSNumber，而不是 NSString。

UIPickerView 显示但不加载数据

UIPickerView shows up but does not load data

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