Multiple Buttons on a Navigation Bar

本文详细介绍了如何在iOS导航栏中使用标准图标和按钮,通过使用`UIBarButtonItem`类,展示如何在导航栏右侧放置多个按钮,包括创建自定义视图、使用`initWithCustomView:`初始化方法以及如何利用`UIToolbar`容器来实现这一目标。
Previously, I wrote about how to use standard icons in your navigation bar. This takes advantage of the nav bar's ability to put a button on the right side. But what if you want to put multiple buttons there? If your title is short enough, you can easily fit 2 or 3 buttons in that space. The nav bar allows you to stick content on the right hand side via the rightBarButtonItem property. On the surface, you might think you can add but one button to this property. But it's not so. There is an initializer for UIBarButtonItem that takes a view:
initWithCustomView:(UIView *)customView
With this, you can create multiple UIButton objects, add them to a UIView, and then create a UIBarButtonItem passing in this parent UIView. The following pseudo-code shows what I mean:
// create the container
UIView* container = [[UIView alloc] init];

// create a button and add it to the container
UIButton* button = [[UIButton alloc] init...];
[container addSubview:button];
[button release];

// add another button
button = [[UIButton alloc] init...];
[container addSubview:button];
[button release];

// now create a Bar button item
UIBarButtonItem* item = [[UIBarButtonItem alloc] initWithCustomView:container];

// set the nav bar's right button item
self.navigationItem.rightBarButtonItem = item;
[item release];

But, what if you want multiple *standard* buttons. Access to the standard buttons/icons is through the UIBarButtonItem class, not UIButton. You can't add UIBarButtonItem objects to a UIView. While there is support to create a UIBarButtonItem object from a UIView-derived object, there does not seem to be a way to do the opposite; there is no way to create a UIView object from a UIBarButtonItem. The only way I found how to deal with multiple UIBarButtonItem objects is to stick them in a toolbar. A UIToolBar is designed to hold multiple UIBarButtonItem objects. Think of a toolbar as your container, instead of the UIView object. And since a UIToolBar is UIView based, it can be added to the right side of a nav bar using the above trick. The following code shows how you can add two standard buttons to the right side:

// create a toolbar to have two buttons in the right
UIToolbar* tools = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, 133, 44.01)];

// create the array to hold the buttons, which then gets added to the toolbar
NSMutableArray* buttons = [[NSMutableArray alloc] initWithCapacity:3];

// create a standard "add" button
UIBarButtonItem* bi = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:NULL];
bi.style = UIBarButtonItemStyleBordered;
[buttons addObject:bi];
[bi release];

// create a spacer
bi = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
[buttons addObject:bi];
[bi release];

// create a standard "refresh" button
bi = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh target:self action:@selector(refresh:)];
bi.style = UIBarButtonItemStyleBordered;
[buttons addObject:bi];
[bi release];

// stick the buttons in the toolbar
[tools setItems:buttons animated:NO];

[buttons release];

// and put the toolbar in the nav bar
self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:tools];
[tools release];

先展示下效果 https://pan.quark.cn/s/5061241daffd 在使用Apache HttpClient库发起HTTP请求的过程中,有可能遇到`HttpClient`返回`response`为`null`的现象,这通常暗示着请求未能成功执行或部分资源未能得到妥善处理。 在本文中,我们将详细研究该问题的成因以及应对策略。 我们需要掌握`HttpClient`的运作机制。 `HttpClient`是一个功能强大的Java库,用于发送HTTP请求并接收响应。 它提供了丰富的API,能够处理多种HTTP方法(例如GET、POST等),支持重试机制、连接池管理以及自定义请求头等特性。 然而,一旦`response`对象为`null`,可能涉及以下几种情形:1. **连接故障**:网络连接未成功建立或在请求期间中断。 需要检查网络配置,确保服务器地址准确且可访问。 2. **超时配置**:若请求超时,`HttpClient`可能不会返回`response`。 应检查连接和读取超时设置,并根据实际需求进行适当调整。 3. **服务器故障**:服务器可能返回了错误状态码(如500内部服务器错误),`HttpClient`无法解析该响应。 建议查看服务器日志以获取更多详细信息。 4. **资源管理**:在某些情况下,如果请求的响应实体未被正确关闭,可能导致连接被提前释放,进而使后续的`response`对象为`null`。 在使用`HttpClient 3.x`版本时,必须手动调用`HttpMethod.releaseConnection()`来释放连接。 而在`HttpClient 4.x`及以上版本中,推荐采用`EntityUtils.consumeQuietly(respons...
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