Fragment arguments 使用kotlin 委托传值

FragmentArgumentDelegate.kt

package com.example.myapplication

import android.os.Binder
import android.os.Bundle
import androidx.core.app.BundleCompat
import androidx.fragment.app.Fragment
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

/**
 * Eases the Fragment.newInstance ceremony by marking the fragment's args with this delegate
 * Just write the property in newInstance and read it like any other property after the fragment has been created
 */

class FragmentArgumentDelegate<T : Any> : ReadWriteProperty<Fragment, T> {

    override operator fun getValue(thisRef: Fragment, property: KProperty<*>): T {
        val args = thisRef.arguments ?: throw IllegalStateException("Cannot read property ${property.name} if no arguments have been set")
        @Suppress("UNCHECKED_CAST")
        return args.get(property.name) as T? ?: throw IllegalStateException("Property ${property.name} could not be read")
    }

    override operator fun setValue(thisRef: Fragment, property: KProperty<*>, value: T) {
        if (thisRef.arguments == null) {
            thisRef.arguments = Bundle()
        }

        val args = thisRef.arguments!!
        val key = property.name

        when (value) {
            is Boolean -> args.putBoolean(key, value)
            is BooleanArray -> args.putBooleanArray(key, value)
            is String -> args.putString(key, value)
            is Int -> args.putInt(key, value)
            is Short -> args.putShort(key, value)
            is Long -> args.putLong(key, value)
            is Byte -> args.putByte(key, value)
            is ByteArray -> args.putByteArray(key, value)
            is Char -> args.putChar(key, value)
            is CharArray -> args.putCharArray(key, value)
            is CharSequence -> args.putCharSequence(key, value)
            is Float -> args.putFloat(key, value)
            is Bundle -> args.putBundle(key, value)
            is Binder -> BundleCompat.putBinder(args, key, value)
            is android.os.Parcelable -> args.putParcelable(key, value)
            is java.io.Serializable -> args.putSerializable(key, value)
            else -> throw IllegalStateException("Type ${value.javaClass.canonicalName} of property ${property.name} is not supported")
        }
    }
}

WeatherCityFragment .kt

package com.example.myapplication


import android.os.Bundle
import androidx.widget.Toast

/**
 * Example usage of FragmentArgumentDelegate
 */
class WeatherCityFragment : Fragment() {

    private var cityId : String by FragmentArgumentDelegate()

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        Toast.makeText(activity, cityId, Toast.LENGTH_SHORT).show()
    }

    companion object {
        fun instance(cityId: String) = WeatherCityFragment().apply {
            this.cityId = cityId
        }
    }
}