我正在用 2 个组件创建 UIPickerView，分分钟和秒。我在 UI 中创建了选择器并想用数据填充它，下面是我如何用 0 - 59 的数字填充它的代码。我想让它看起来像圆形，这就是为什么 kSizeOfPicker 是 60000。当用户按下按钮窗口时选择器出现但它会大大减慢应用程序的速度，因为这 代码在 viewDidLoad 中。我该如何解决？

NSString *stringValue = [[NSString alloc] init];

for(int i=0; i<kSizeOfPicker; i++)
{
    stringValue = [NSString stringWithFormat:@"%d", i%60];


    [_minutesArray addObject:stringValue];
    [_secondsArray addObject:stringValue];
}

这里是数据源和委托(delegate)方法:

#pragma mark - UIPickerView DataSource Methods


- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
return 2;
}


- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent :    (NSInteger)component
{

if (component==0)
{
    return [_minutesArray count];
}
else
{
    return [_secondsArray count];
}

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
NSString *title;
switch (component)
{

    case 0:
        title = [NSString stringWithFormat:@"%@ minutes", [_minutesArray objectAtIndex:row]];

        return title;
        break;
    case 1:
        title = [NSString stringWithFormat:@"%@ seconds", [_secondsArray objectAtIndex:row]];
        return title;
        break;
}
return nil;
}

#pragma mark - UIPickerView Delegate Methods

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

if (component == 0)
    _firstComponent = [_minutesArray objectAtIndex:row];

else
    _secondComponent = [_secondsArray objectAtIndex:row];

}

最佳答案

您不需要准备 NSArray 中的所有数据来归档循环选择器 View 。 以下代码虚拟地 围绕所选行准备了 +-50 个重复数据集。 在 pickerView:didSelectRow:inComponent: 委托(delegate)方法中，您可以重置所选行。

@interface MyViewController () <UIPickerViewDataSource, UIPickerViewDelegate>
@property (weak, nonatomic) IBOutlet UIPickerView *pickerView;
@property (assign, nonatomic) NSUInteger minutes;
@property (assign, nonatomic) NSUInteger seconds;
@end

@implementation MyViewController

#define VALUE_THRESHOLD 60
#define PICKER_DUPLICATES 100
#define CENTER_ROW (VALUE_THRESHOLD * PICKER_DUPLICATES / 2)

- (void)viewDidLoad {
    [super viewDidLoad];
    [_pickerView selectRow:_minutes + CENTER_ROW inComponent:0 animated:NO];
    [_pickerView selectRow:_seconds + CENTER_ROW inComponent:1 animated:NO];
}

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
    return 2;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
    return VALUE_THRESHOLD * PICKER_DUPLICATES;
}

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component {
    return [NSString stringWithFormat:@"%d", row % VALUE_THRESHOLD];
}

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
    NSInteger actualRow = row % VALUE_THRESHOLD;

    // reset to center dataset
    [pickerView selectRow: actualRow + CENTER_ROW inComponent:component animated:NO];

    // do anything what you want;
    if(component == 0) {
        _minutes = actualRow;
    }
    else {
        _seconds = actualRow;
    }
}

@end

关于ios - 如何优化代码并快速加载 UIPickerView 数据？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24795700/