导航栏控制器的渐变

Bertha 。 2022-05-21 11:10 205阅读 0赞

效果图  
![导航栏渐变][70]

实现步骤  
1、设置导航栏视图控制器中的`navigationBar`背景图标

[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];

2、设置导航栏视图控制器中的`navigationBar`子视图的背景颜色

barView = self.navigationController.navigationBar.subviews.firstObject;
    barView.backgroundColor = [UIColor redColor];

3、实现代理方法`- (void)scrollViewDidScroll:(UIScrollView *)scrollView`并在该方法中根据滑动偏移量计算背景色的透明度

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
    {
        CGFloat offY = scrollView.contentOffset.y;
        NSLog(@"offY: %f", offY);
    
        // 1
        if (offY >= 300.0) {
            barAlpha = 1.0;
        } else if (offY >= 0) {
            barAlpha = offY / 300.0;
        } else {
            barAlpha = 0.0;
        }
        barView.backgroundColor = [[UIColor redColor] colorWithAlphaComponent:barAlpha];
    }

代码示例

@interface NavViewController () <UITableViewDelegate, UITableViewDataSource>
    {
        UITableView *tableview;
    
        CGFloat barAlpha;
        UIView *barView;
    }
    
    @end
    
    @implementation NavViewController
    
    - (void)viewDidLoad {
        [super viewDidLoad];
        // Do any additional setup after loading the view.
    
        self.navigationItem.title = @"导航栏渐变";
    
        self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"bottom" style:UIBarButtonItemStyleDone target:self action:@selector(bottomClick)];
    
        // 隐藏分割线
        self.navigationController.navigationBar.shadowImage = [UIImage new];
        // 设置导航栏背景图标
        [self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
        // 设置导航栏背景透明度
        barAlpha = 0.0;
        barView = self.navigationController.navigationBar.subviews.firstObject;
        barView.backgroundColor = [UIColor redColor];
    
        //
        tableview = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStylePlain];
        [self.view addSubview:tableview];
        tableview.autoresizingMask = UIViewAutoresizingFlexibleHeight;
        tableview.backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"tableBground"]];
        tableview.delegate = self;
        tableview.dataSource = self;
    }
    
    - (void)didReceiveMemoryWarning {
        [super didReceiveMemoryWarning];
        // Dispose of any resources that can be recreated.
    }
    
    - (void)dealloc
    {
        NSLog(@"dealloc: %@", self);
    }
    
    - (void)bottomClick
    {
        [tableview setContentOffset:CGPointMake(0.0, (tableview.contentSize.height - tableview.bounds.size.height)) animated:YES];
    }
    
    - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
    {
        return 100;
    }
    
    - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
    {
        UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"UITableViewCell"];
        if (cell == nil)
        {
            cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"UITableViewCell"];
            cell.backgroundColor = [UIColor colorWithWhite:0.5 alpha:0.5];
        }
        cell.textLabel.text = [NSString stringWithFormat:@"row: %@", @(indexPath.row + 1)];
        return cell;
    }
    
    - (BOOL)tableView:(UITableView *)tableView shouldHighlightRowAtIndexPath:(NSIndexPath *)indexPath
    {
        return NO;
    }
    
    - (void)scrollViewDidScroll:(UIScrollView *)scrollView
    {
        CGFloat offY = scrollView.contentOffset.y;
        if (offY >= 300.0) {
            barAlpha = 1.0;
        } else if (offY >= 0) {
            barAlpha = offY / 300.0;
        } else {
            barAlpha = 0.0;
        }
        barView.backgroundColor = [[UIColor redColor] colorWithAlphaComponent:barAlpha];
    }
    
    @end

[70]: /images/20220521/bc292c1a103a4eefa2f896d39a804d94.png