在为设置页面创建 Activity 后,我注意到 if (mCurrentValue !== value)
中的 mCurrentValue !== value
返回警告:
Identity equality for arguments of types Boolean? and Boolean can be unstable because of implicit boxing
我尝试通过在 override fun onXchange(value:Boolean) {
中的 Boolean
旁边添加一个 ?
来解决此警告,但随后返回以下错误:
'onXchange' overrides nothing
关于如何解决这个问题有什么想法吗?
Activity 类
import android.content.Intent
import android.graphics.Color
import android.graphics.drawable.ColorDrawable
import android.os.Bundle
import android.preference.PreferenceManager
import android.support.v7.app.AppCompatActivity
import android.view.MenuItem
class MySettingsActivity : AppCompatActivity(), MySettingsFragment.PreferenceXchangeListener {
private var mCurrentValue: Boolean? = null
override fun onCreate(savedInstanceState: Bundle?) {
val mSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this)
mCurrentValue = mSharedPreferences.getBoolean("preference_a", false)
if (mCurrentValue as Boolean)
{
setTheme(R.style.MyDarkAppCompatTheme)
}
else
{
setTheme(R.style.MyLightAppCompatTheme)
}
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_mysettings)
val settingsFragment = MySettingsFragment()
supportFragmentManager
.beginTransaction()
.replace(R.id.settings_container, settingsFragment)
.commit()
val myActionBar = actionBar
if (myActionBar != null)
{
myActionBar.setTitle(R.string.settings)
myActionBar.setBackgroundDrawable(ColorDrawable(Color.BLACK))
myActionBar.setDisplayHomeAsUpEnabled(true)
myActionBar.setDisplayShowHomeEnabled(true)
myActionBar.setHomeAsUpIndicator(resources.getDrawable(R.drawable.ic_arrow_back_white, null))
}
}
override fun onXchange(value:Boolean?) {
if (mCurrentValue !== value) {
mCurrentValue = value
recreate()
}
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
when (item.itemId) {
android.R.id.home -> {
val intent = parentActivityIntent
intent?.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION)
onBackPressed()
return true
}
else ->
return super.onOptionsItemSelected(item)
}
}
}
fragment 类
class MySettingsFragment : PreferenceFragmentCompat(), Preference.OnPreferenceChangeListener {
override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
addPreferencesFromResource(R.xml.app_preferences)
val mCheckBoxPreference = findPreference("preference_a") as CheckBoxPreference
mCheckBoxPreference.onPreferenceChangeListener = this
}
private var mPreferenceXchangeListener: PreferenceXchangeListener? = null
interface PreferenceXchangeListener {
fun onXchange(value:Boolean)
}
override fun onAttach(context: Context) {
super.onAttach(context)
try
{
mPreferenceXchangeListener = context as MySettingsFragment.PreferenceXchangeListener
}
catch (e:ClassCastException) {
Log.e(TAG, "onAttach::::: PreferenceXchangeListener must be set in parent Activity")
}
}
override fun onPreferenceChange(preference: Preference, newValue:Any):Boolean {
val preferenceKey = preference.key
if (preferenceKey == "preference_a")
{
(preference as CheckBoxPreference).isChecked = newValue as Boolean
mPreferenceXchangeListener!!.onXchange(newValue)
return true
}
return false
}
companion object {
private val TAG = MySettingsFragment::class.java.simpleName
}
}
最佳答案
所以首先我可以解释它描述的问题。让我们提出一个非常人为的场景:
BooleanProvider.java
class BooleanProvider {
@NonNull Boolean wrapMyBoolean(boolean state) {
return new Boolean(state);
}
}
BooleanProviderTest.kt
class BooleanProviderTest {
@Test fun `it returns a true value when true is provided`() {
assertSame(BooleanProvider().wrapMyBoolean(true), true)
}
}
这个测试实际上会失败,因为 Boolean
的实例不一样。在 Java 代码中,我们初始化了一个新的 Boolean
实例(而不是静态定义的 Boolean.TRUE
和 Boolean.FALSE
实例)当一个原语被自动装箱到一个 java.lang.Boolean
时,你会得到)。因此,为避免潜在的意外结果,建议您不要通过引用来比较这些类型。
最简单的解决方法是将相等性测试更改为 !=
而不是 !==
。这将执行身份相等性测试而不是引用相等性测试,并将适本地处理任一侧的空值。无论如何,这就是您在 99% 的时间里想要的。
其次,如果您不需要以特定方式处理空值,您也可以只将mCurrentValue
声明为非空类型,并为其指定一个默认值。只需将其声明为:
private var mCurrentValue: Boolean = false // false is the default here
关于android - 创 build 置 Activity 时出现 boolean 参数问题,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/53635745/