如何替代sizeToFit使键盘inputAccessoryView工具栏按钮均匀分布？

我参考Paul Hudson的代码，在Objective-C遗留项目中为UITextView的inputAccessoryView添加了UIToolbar。但使用sizeToFit方法后，工具栏上的图标并未均匀分布，而是左对齐。我希望四个图标能像示例那样从左到右均匀排列，以下是我的代码，该代码在ViewDidLoad中调用：

-(void)addToolBarToKeyboardOfTextView: (UITextView*)view {
    UIImage *addimg = [UIImage imageNamed:@"addimage"];
    UIImage *addfile = [UIImage imageNamed:@"addfile"];
    UIImage *showtip = [UIImage imageNamed:@"showtip"];
    UIImage *close = [UIImage imageNamed:@"close"];
    
    UIToolbar *bar = [[UIToolbar alloc] init];
    UIBarButtonItem *addImage = [[UIBarButtonItem alloc] initWithImage:addimg style:UIBarButtonItemStylePlain target:self action:@selector(selectPhoto)];
    UIBarButtonItem *attachFile = [[UIBarButtonItem alloc] initWithImage:addfile style:UIBarButtonItemStylePlain target:self action:@selector(selectFile)];
    UIBarButtonItem *showTip = [[UIBarButtonItem alloc] initWithImage:showtip style:UIBarButtonItemStylePlain target:self action:@selector(showTip)];
    UIBarButtonItem *close = [[UIBarButtonItem alloc] initWithImage:close style:UIBarButtonItemStylePlain target:self action:@selector(closeSelf)];
   
    bar.items = @[addImage,attachFile,showtip,close];
    [bar sizeToFit];
    view.inputAccessoryView = bar;
}

当前inputAccessoryView可正常显示，但图标左对齐而非均匀分布。请问如何实现图标均匀排列？

要让工具栏按钮均匀分布，核心是利用弹性空间UIBarButtonItem填充按钮间的空隙，自动均分剩余宽度。具体修改如下：

1. 创建UIBarButtonSystemItemFlexibleSpace类型的弹性空间项，这类项会自动拉伸填充空白区域
2. 在功能按钮的首尾、以及每两个按钮之间插入弹性空间
3. 修复原代码中的变量名冲突和数组元素错误问题

修改后的完整代码：

-(void)addToolBarToKeyboardOfTextView: (UITextView*)view {
    UIImage *addimg = [UIImage imageNamed:@"addimage"];
    UIImage *addfile = [UIImage imageNamed:@"addfile"];
    UIImage *showtipImg = [UIImage imageNamed:@"showtip"];
    UIImage *closeImg = [UIImage imageNamed:@"close"];
    
    UIToolbar *bar = [[UIToolbar alloc] init];
    UIBarButtonItem *addImage = [[UIBarButtonItem alloc] initWithImage:addimg style:UIBarButtonItemStylePlain target:self action:@selector(selectPhoto)];
    UIBarButtonItem *attachFile = [[UIBarButtonItem alloc] initWithImage:addfile style:UIBarButtonItemStylePlain target:self action:@selector(selectFile)];
    UIBarButtonItem *showTip = [[UIBarButtonItem alloc] initWithImage:showtipImg style:UIBarButtonItemStylePlain target:self action:@selector(showTip)];
    UIBarButtonItem *closeBtn = [[UIBarButtonItem alloc] initWithImage:closeImg style:UIBarButtonItemStylePlain target:self action:@selector(closeSelf)];
    
    // 创建弹性空间
    UIBarButtonItem *flexibleSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];
    
    // 组装按钮数组：首尾+按钮间插入弹性空间
    bar.items = @[flexibleSpace, addImage, flexibleSpace, attachFile, flexibleSpace, showTip, flexibleSpace, closeBtn, flexibleSpace];
    [bar sizeToFit];
    view.inputAccessoryView = bar;
}

原代码问题说明 #

• 变量名冲突：原代码中UIImage *close和UIBarButtonItem *close重名，会引发编译警告，已修改为closeImg和closeBtn
• 数组元素错误：原数组中showtip是UIImage对象，不是UIBarButtonItem，会导致运行崩溃，已替换为showTip按钮对象

修改后，弹性空间会自动均分工具栏的剩余宽度，四个功能按钮就能实现从左到右的均匀排列效果。

内容的提问来源于stack exchange，提问作者user6631314