Question

有谁能告诉我为什么这段代码不起作用？

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：

leftBarButtonItem上没有任何内容。这就是问题所在。

Answer 1

这应该有效

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;

Answer 2

来自文档：

“创建自定义按钮时 - 这是一个类型为UIButtonTypeCustom的按钮 - 按钮的框架最初设置为（0,0,0,0）。在将按钮添加到界面之前，您应该更新框架到更合适的价值。“

所以如果你在第2行设置框架，你应该看到一些东西，例如：

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

将自定义按钮添加到UINavigationItem LeftBarButtonItem

2 个答案: