任何操作方法，當文本字段爲空的iOS

Question

當文本字段爲空，用戶點擊後退按鈕將它調用的操作方法？我的要求是當用戶點擊後退按鈕，文本字段爲空時，光標將位於前一個文本字段上。

Answer 1

我認爲你需要添加一個自定義後退按鈕並定義它的動作。

UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom]; 
[backButton setFrame:CGRectMake(0,0,30,30)]; 
backButton.contentHorizontalAlignment = UIControlContentHorizontalAlignmentLeft; 

[backButton addTarget:self action:@selector(backBtnClicked:) forControlEvents:UIControlEventTouchUpInside]; 

UIBarButtonItem *barBackButtonItem = [[UIBarButtonItem alloc] initWithCustomView:backButton]; 

navitem.hidesBackButton = YES; 

navitem.leftBarButtonItems = @[barBackButtonItem];