iOS UI布局-回到顶部

回到顶部，是比较常用的一个效果

核心代码

在ViewDidLoad中，添加回到顶部按钮

计算偏移量，如果当前显示的内容全部向上隐藏掉，则显示“回到顶部”按钮

//
//  ViewController.m
//  回到顶部
//
//  Created by Apple on 15/11/4.
//  Copyright © 2015年 Apple. All rights reserved.
//

#import "ViewController.h"

@interface ViewController () <UITableViewDelegate,UITableViewDataSource>
@property(nonatomic, strong)UITableView        *tableView;
@property (nonatomic, strong) UIButton * topBtn;
@property (nonatomic, assign) CGFloat lastContentOffset;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.tableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
    self.tableView.delegate = self;
    self.tableView.dataSource = self;
    [self.view addSubview:_tableView];
    
    
    // 添加回到顶部按钮
    _topBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    _topBtn.frame = CGRectMake(self.view.frame.size.width-60, self.view.frame.size.height-100, 40, 40);
    [_topBtn setBackgroundImage:[UIImage imageNamed:@"nearby_return_top_btn"] forState:UIControlStateNormal];
    [_topBtn addTarget:self action:@selector(backToTopButton) forControlEvents:UIControlEventTouchUpInside];
    _topBtn.clipsToBounds = YES;
    _topBtn.hidden = YES;
    [self.view addSubview:_topBtn];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return 60;
}

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CMainCell = @"CMainCell";
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CMainCell];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CMainCell];
    }

    cell.textLabel.text =[NSString stringWithFormat:@"测试广本%u",indexPath.row];
    return cell;
}


// MARK:  计算偏移量
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    //MARK:列表滑动偏移量计算
    CGPoint point = [self.tableView contentOffset];
    
    if (point.y >= self.tableView.frame.size.height) {
        self.topBtn.hidden = NO;
        [self.view bringSubviewToFront:self.topBtn];
    } else {
        self.topBtn.hidden = YES;
    }
}

//MARK: 点击移动到顶部
- (void)backToTopButton{
    [self.tableView setContentOffset:CGPointMake(0, 0) animated:YES];
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

效果：

源代码下载链接：http://pan.baidu.com/s/1c0c7t3E