IOS开发基础UIPickerView循环显示

本文适合对UIPickerView已经有一定了解的读者阅读。

核心思想是：整数倍扩大UIPickerView的显示区域范围，且显示的数据索引通过取余数获得。

下面是实现代码：

1.ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UIPickerViewDataSource, UIPickerViewDelegate>

@property(strong, nonatomic)UIPickerView *myPickerView;

//显示的实际数据

@property(strong, nonatomic)NSArray *data;

@end

2.ViewController.m

#import "ViewController.h"

#define WIDTH self.view.frame.size.width

#define HEIGHT self.view.frame.size.height

//倍数

#define MULTIPLE 51

@implementation ViewController

- (void)viewDidLoad {

[super viewDidLoad];

self.myPickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(WIDTH*0.40, HEIGHT*0.20, WIDTH*0.20, HEIGHT*0.1)];

//添加代理

self.myPickerView.delegate = self;

self.myPickerView.dataSource = self;

[self.view addSubview:self.myPickerView];

//实际显示数据

NSArray *arr = @[@"1", @"2", @"3", @"4", @"5", @"6", @"7", @"8", @"9", @"10"];

self.data = arr;

//让滚轴显示指定的位置, 中间的位置

[self.myPickerView selectRow:MULTIPLE/2*self.data.count inComponent:0 animated:NO];

}

#pragma mark 实现UIPickerViewDataSource协议

-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{

return 1;

}

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

//使UIPickerView显示的范围扩大MULTIPLE倍

return self.data.count*MULTIPLE;

}

#pragma mark 实现UIPickerViewDelegate的代理方法

//设置当前component和row显示的标题

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

//通过取余数使得显示的实际数据索引被限定在一定范围

return self.data[row % self.data.count];

}

//核心部分，当滚轴滚动超出中间范围时返回回来

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

//中间位置的相对长度

NSInteger length = MULTIPLE/2 * self.data.count;

//返回到中间位置

[self.myPickerView selectRow:row%self.data.count + length inComponent:0 animated:NO];

// NSLog(@"%ld", row%self.data.count + length);

}