将自定义按钮添加到UINavigationItem LeftBarButtonItem

Question

任何人都可以告诉我为什么这段代码不起作用吗？

self.backButton = [UIButton buttonWithType:UIButtonTypeCustom]; 
[self.backButton setImage:[UIImage imageNamed:@"back_arrow.png"] 
       forState:UIControlStateNormal]; 
self.backButton.contentMode = UIViewContentModeCenter; 
[self.backButton addTarget:self 
        action:@selector(backButtonAction:) 
      forControlEvents:UIControlEventTouchUpInside]; 

UIBarButtonItem *backButtonItem = [[UIBarButtonItem alloc] initWithCustomView:self.backButton]; 
[navigationItem setLeftBarButtonItem:backButtonItem animated:NO]; 
navigationItem.hidesBackButton = YES; 

编辑：

没有出现在leftBarButtonItem。那就是问题所在。

Answer 1

从文档：

“当创建自定义按钮，其与按钮的类型UIButtonTypeCustom-的帧被设置为一个按钮（0 ，0,0,0），在将按钮添加到您的界面之前，您应该将帧更新为更合适的值。“

所以，你应该看到的东西，如果你在第2行设置的框架，如：

self.backButton.frame = CGRectMake(0, 0, 40, 20); 

Answer 2

这应该工作

CGRect rect = CGRectMake(10, 0, 30, 30); 
self.backButton = [[UIButton alloc] initWithFrame:rect]; 
[self.backButton setImage:[UIImage imageNamed:@"back_arrow.png"] 
       forState:UIControlStateNormal]; 
self.backButton.contentMode = UIViewContentModeCenter; 
[self.backButton addTarget:self 
        action:@selector(backButtonAction:) 
      forControlEvents:UIControlEventTouchUpInside]; 

UIBarButtonItem *backButtonItem = [[UIBarButtonItem alloc] initWithCustomView:self.backButton]; 
self.navigationItem.leftBarButtonItem = backButtonItem; 
self.navigationItem.hidesBackButton = YES;