iOS UI布局-回到顶部

//
//  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