android - Kotlin - Preference.setOnPreferenceClickListener

Question

我正在尝试在我的 SettingsFragment 中添加一个 onPreferenceClickListener，如果我这样做的话:

signOutPref.setOnPreferenceClickListener(object: Preference.OnPreferenceClickListener {
           override fun onPreferenceClick(preference: Preference?): Boolean {
                    val signOutIntent = Intent(activity, SignInActivity::class.java)
                    startActivity(signOutIntent)
                    return true
                }
            })

它在发出警告时完美运行:

Use property access syntax

如果我这样写:

signOutPref.setOnPreferenceClickListener {
                val signOutIntent = Intent(activity, SignInActivity::class.java)
                startActivity(signOutIntent)
                return true
            }

这应该是完全相同的东西，这是最好的方法，我得到:

The Boolean literal does not conform to the expected type Unit

关于 return true 语句。

我错过了什么？第二种方法与第一种方法不同吗？我该如何摆脱这个错误？

Answer 1

在 lambda 中，最后一条语句自动成为返回值，除非它的返回类型被推断为 Unit。所以只需删除 return。

signOutPref.setOnPreferenceClickListener {
   val signOutIntent = Intent(activity, SignInActivity::class.java)
   startActivity(signOutIntent)
   true
}

文档说:

A lambda expression is always surrounded by curly braces, parameter declarations in the full syntactic form go inside curly braces and have optional type annotations, the body goes after an -> sign. If the inferred return type of the lambda is not Unit, the last (or possibly single) expression inside the lambda body is treated as the return value.