iphone - UIPickerView无限行

Question

如 UIDatePicker 中所示，您可以无限地向上滚动(也可以向下滚动)。我也想实现这一目标，因为我希望人们选择一个日期，例如:

2010 年 1 月 1 日2010 年 1 月 2 日...2010年12月30日2010年12月31日2011 年 1 月 1 日..

所以它可以永远持续下去。我将如何实现这个目标？因为我只能在委托(delegate)中给出特定数量的行。

Answer 1

我认为您实际上无法创建 UIPickerView 循环，但我过去所做的方法是从 numberOfRowsInComponent 返回一个非常大的数字，然后计算row 从 viewForRow 返回适当的 View ，如下所示:

// picker data source:
-(NSInteger) pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger) component
{
    // to make it look like the picker is looping indefinetly,
    // we give it a really large length, and then in the picker delegate we consider
    // the row % (actual length) instead of just the row.
    return INT16_MAX;
}


// picker delegate:
-(UIView *) pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger) row forComponent:(NSInteger) component reusingView:(UIView *)view
{
    // to make it look like the picker is looping indefinetly,
    // we give it a really large length in the picker data source, and then we consider
    // the row % actual_length instead of just the row.
    row = row % actual_length;
    // where actual length is the number of options that will be looping

    // ... do whatever
}

并在初始化中:

- (void)viewDidLoad {
    [super viewDidLoad];

    // ... whatever other initialization... 

    // to make it look like the picker is looping indefinetly ,
    // we give it a really large length in the picker data source, and then we consider
    // the row % actual_length instead of just the row, 
    // and we start with the selection right in the middle, rounded to the
    // first multiple of actual_length so we start the selection on 
    // the first option in the list.
    [myPicker selectRow:(INT16_MAX/(2*actual_length))*actual_length inComponent:0 animated:NO];
}