UIScroView3倍的contentSize，左右Scroll時，懶惰加載View

2019-11-14 20:37:26

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UIScroView 3倍的contentSize，左右Scroll時，懶惰添加左右的View

用途：分段加載數據

定義枚舉：

typedefenum {    ViewPositionLeft = 101,    ViewPositionCenter,    ViewPositionRight} ViewPosition;

變量定義：

    NSInteger _currnetPage;    CGRect _leftFrame;    CGRect _centerFrame;    CGRect _rightFrame;    UIScrollView *_sv;

初始化變量：

-(void)createView{     _currnetPage = 0;        _sv = [[UIScrollView alloc] init];    _sv.frame = CGRectMake(0, 0, 320, 424);    _sv.pagingEnabled = YES;    _sv.backgroundColor = [UIColorwhiteColor];    _sv.contentSize = CGSizeMake(_sv.frame.size.width*3, _sv.frame.size.height);        _sv.showsHorizontalScrollIndicator = YES;    _sv.showsVerticalScrollIndicator = NO;         for (int i = 2; i > -1; i--) {        CGRect frame;        frame.origin.x = _sv.frame.size.width * (2 - i);        frame.origin.y = 0;        frame.size = _sv.frame.size;                UIView *lbl = [selfcreateLabeViewWithCurrentPage:i];        lbl.frame = frame;                if (i == 2) {            _leftFrame = frame;            lbl.tag = ViewPositionLeft;                    }        if (i == 1) {            _centerFrame = frame;            lbl.tag = ViewPositionCenter;        }        if (i == 0) {            _rightFrame = frame;            lbl.tag = ViewPositionRight;        }                        [_sv addSubview:lbl];                    }    _sv.delegate = self;                    [_svscrollRectToVisible:_rightFrameanimated:NO];        [self.view addSubview:_sv];}

創建新View的方法（selfcreateLabeViewWithCurrentPage）：

- (UIView *)createLabeViewWithCurrentPage:(int)Page{        UILabel *textView = [[UILabel alloc] init];    textView.text = [NSString stringWithFormat:@"Page %d",Page];    textView.font = [UIFont systemFontOfSize:38];    textView.textColor = [UIColor blackColor];    textView.backgroundColor = [UIColorwhiteColor];    textView.textAlignment = UITextAlignmentCenter;     [_sv addSubview:textView];    return textView;}UIScrollViewDelegate方法：- (void)scrollViewDidEndDecelerating:(UIScrollView *)sv{            BOOL towardsToLeft = NO;    CGFloat width = _sv.frame.size.width;        if (_sv.contentOffset.x == width) {        if (_currnetPage == 0) {            _currnetPage++;        }                return;    }    if (_sv.contentOffset.x > width) {        towardsToLeft = YES;        if(_currnetPage == 0){//            NSLog(@"currentPage = 0;  向左");            return;        }//        NSLog(@"向左");    }    else{//        NSLog(@"向右");    }        //    _PReviousPage = _currnetPage;    if (towardsToLeft == YES) {        _currnetPage--;    }    else{        _currnetPage++;    }            if (_currnetPage == 0) {                    }    else  {        [sv scrollRectToVisible:_centerFrameanimated:NO];        UIView *view = [_sv viewWithTag:_currnetPage];        view.frame = _centerFrame;                if (towardsToLeft == YES) {            UIView *viewRLeft = [_sv viewWithTag:ViewPositionLeft];            [viewRLeft removeFromSuperview];                        UIView *viewRCenter = [_sv viewWithTag:ViewPositionCenter];            viewRCenter.frame = _leftFrame;            viewRCenter.tag = ViewPositionLeft;                        UIView *viewRRight = [_sv viewWithTag:ViewPositionRight];            viewRRight.frame = _centerFrame;            viewRRight.tag = ViewPositionCenter;                        UIView *viewRight = [self createLabeViewWithCurrentPage:_currnetPage - 1];            viewRight.frame = _rightFrame;            viewRight.tag = ViewPositionRight;            [sv addSubview:viewRight];        }        else{            UIView *viewRRight = [_sv viewWithTag:ViewPositionRight];            [viewRRight removeFromSuperview];                        UIView *viewRCenter = [_sv viewWithTag:ViewPositionCenter];            viewRCenter.frame = _rightFrame;            viewRCenter.tag = ViewPositionRight;                        UIView *viewRLeft = [_sv viewWithTag:ViewPositionLeft];            viewRLeft.frame = _centerFrame;            viewRLeft.tag = ViewPositionCenter;                        UIView *viewLeft = [self createLabeViewWithCurrentPage:_currnetPage + 1];            viewLeft.frame = _leftFrame;            viewLeft.tag = ViewPositionLeft;            [sv addSubview:viewLeft];                                            }    } }