//
//  ViewController.m
//  ScrollView循環(huán)利用
//
//  Created by 高新強 on 15/11/19.
//  Copyright ? 2015年 Gavin. All rights reserved.
//

#import "ViewController.h"

#define kCount 8
@interface ViewController ()<UIScrollViewDelegate>
@property (weak, nonatomic) IBOutlet UIScrollView *scrollView;

@property (weak, nonatomic) UIImageView *centerImageV;
@property (weak, nonatomic) UIImageView *reuseImageV;



@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    
    //圖片的寬度
    CGFloat w = self.view.frame.size.width;
    //圖片的高度
    CGFloat h = self.view.frame.size.height;
    
    //設置ScrollView初始化屬性
    //設置分頁效果
    self.scrollView.pagingEnabled = YES;
    //初始化ScollView的內容大小
    self.scrollView.contentSize = CGSizeMake(3 * w, h);
    //隱藏垂直滾動條
    self.scrollView.showsVerticalScrollIndicator = NO;
    //設置ScrollView代理
    self.scrollView.delegate = self;
    
    //創(chuàng)建一個可見的UIImageView(也就是中間的UIImageView)
    UIImageView *centerImageV = [[UIImageView alloc] init];
    //記錄住中間的centerImageV.
    self.centerImageV = centerImageV;
    //設置一張默認圖片
    self.centerImageV.image = [UIImage imageNamed:@"00"];
    //設置中間圖片的x值為一個屏幕的寬度
    self.centerImageV.frame = CGRectMake(w, 0, w, h);
    //給圖片綁定一個標識.
    self.centerImageV.tag = 0;
    //把圖片添加到ScrollView上.
    [self.scrollView addSubview:self.centerImageV];
    
    
    
    //創(chuàng)建一個可重復利用的UIImageView,也就是一下滾動出來的圖片.
    UIImageView *reuseImageV = [[UIImageView alloc] init];
    //記錄住reuseImageV
    self.reuseImageV = reuseImageV;
    //把它的位置設置到最左側.也就是0,0的位置,讓它的大小和當前ScrollView的大小一樣.
//    self.reuseImageV.image = [UIImage imageNamed:@"01"];
    self.reuseImageV.frame = self.view.bounds;
    
    //把圖片添加到ScrollView上.
    [self.scrollView addSubview:self.reuseImageV];
    
    
    //初始化scrollView的偏移量.一開始顯示中間部分.
    self.scrollView.contentOffset = CGPointMake(w, 0);

}

//當ScorllView滾動時調用.
-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
    
    //獲取ScrollView X軸方向的偏移量
    CGFloat offsetX = scrollView.contentOffset.x;
    //記錄ScollView的寬度.
    CGFloat w = scrollView.frame.size.width;
    
    //設置循環(huán)利用View的位置.
    CGRect reuserImageVFrame = self.reuseImageV.frame;
    //記錄當前是第幾頁
    NSInteger index = 0;
    
    //判斷是向左滾動還是向右滾動
    if(offsetX > self.centerImageV.frame.origin.x){
        //如果是向右滾動
        //讓重復利用的圖片X在中間ImageView的后面.
        reuserImageVFrame.origin.x = CGRectGetMaxX(self.centerImageV.frame);
        //設置頁數(shù)+1.
        index = self.centerImageV.tag + 1;
        if (index > kCount - 1) {
            //如果頁數(shù)大于總個數(shù).從第0頁開始.
            index = 0;
        }
        
    }else{
        //如果是向左滾動.
        //設置重復利用的圖片X在左側,0的位置
        reuserImageVFrame.origin.x = 0;
        //設置頁數(shù)-1
        index = self.centerImageV.tag - 1;
        //如果頁數(shù)小于0頁.
        if(index < 0){
            //從最后一頁開始.
            index = kCount - 1;
        }
    }
    
    //設置重復利用的圖片的位置
    self.reuseImageV.frame = reuserImageVFrame;
    //記錄當前重復利用的圖片是第幾頁
    _reuseImageV.tag = index;
    NSLog(@"%ld",index);
    //設置圖片名稱
    NSString *imageName = [NSString stringWithFormat:@"0%ld",index];
    //設置重復利用的圖片
    self.reuseImageV.image = [UIImage imageNamed:imageName];
    
    //設置如果滾動到最左側,或者滾動的最右側.
    if(offsetX <= 0 || offsetX >= 2 * w){
        
        //交換中間的圖片 和 重復利用圖片兩個對象.
        UIImageView *temp = self.centerImageV;
        self.centerImageV = self.reuseImageV;
        self.reuseImageV = temp;
        
        //交換兩個圖片的位置.
        self.centerImageV.frame = self.reuseImageV.frame;
        //初始化scrollView的偏移量.一開始顯示中間部分.
        self.scrollView.contentOffset = CGPointMake(w, 0);
    }
}

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

@end