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创建设置活动时出现布尔参数问题

boolean kotlin android-activity android

wbk727 · 技术社区 · 6 年前

在为设置页面创建活动后,我注意到, mCurrentValue !== value if (mCurrentValue !== value) 返回警告:

布尔型参数的标识相等?由于隐式装箱,布尔值可能不稳定

我试图通过添加一个 ? Boolean 在里面 override fun onXchange(value:Boolean) {

关于如何解决这个问题有什么想法吗?

活动课

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)
        }
    }
}

片段类

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
    }
}

1 回复 | 直到 6 年前

Kevin Coppock 6 年前

BooleanProvider.java

class BooleanProvider {
    @NonNull Boolean wrapMyBoolean(boolean state) {
        return new Boolean(state);
    }
}

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 它们不一样。在Java代码中,我们初始化了 布尔值 (而不是静态定义的 Boolean.TRUE 和 Boolean.FALSE 将基本体自动装箱到 java.lang.Boolean )。因此,为了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。

!= 而不是 !== . 这将执行标识相等测试而不是引用相等测试,并将适当地处理任意一侧的空值。不管怎样,99%的时间你都想要这样。

mCurrentValue 如果不需要以特定方式处理null值,则将其作为非null类型,并为其指定一个默认值。只需声明如下:

private var mCurrentValue: Boolean = false // false is the default here