如何使用泛型或反射来显示/隐藏片段？ Kotlin Android

Question

I have a fragment manager to show/hide fragments in my app. Right now when I want to show a fragment from any activity or fragment I call this method from the manager

 fun show(manager: FragmentManager, fragmentTag: String, container: Int, data: Any?): Companion {
        var fragment = manager.findFragmentByTag(fragmentTag)
        if (fragment != null) {
            manager.popBackStack(fragmentTag, 0)
        } else {
            addFragment(manager, getFragment(fragmentTag, manager, data)!!, container, fragmentTag)
        }
        return this
    }

 private fun getFragment(fragmentTag: String, manager: FragmentManager, data: Any?): Fragment? {
        when (fragmentTag) {
            MenuFragment.TAG -> return getMenuFragment(manager)
            TagsFragment.TAG -> return getTagsFragment(manager)
            ...
        }
        return null
    }

with return a fragment with a specific class

private fun getMenuFragment(manager: FragmentManager): Fragment {
        var fragment = manager.findFragmentByTag(MenuFragment.TAG) as MenuFragment?
        if (fragment == null) {
            fragment = MenuFragment.newInstance()
        }
        return fragment
    }

I would like to have an strategy to avoid create one method every time I need to implement a new fragment, so I was thinking about generics or maybe reflection wich I have never used before.

Is there any way to do this using reflection? or another better strategy?

Thanks for any help.

Edit

As I have one Activity and many fragments I finally extended FragmentManager to use it in every fragment.

inline fun <reified T : Fragment> FragmentManager.showFragment(tag: String, container: Int, args: Bundle? = null) {
    val clazz = T::class.java
    var fragment = findFragmentByTag(clazz.name)
    if (fragment != null) {
        this.popBackStack(tag, 0)
    } else {
        fragment = (clazz.getConstructor().newInstance() as T).apply {
            args?.let {
                it.classLoader = javaClass.classLoader
                arguments = args
            }
        }
        val transaction = this.beginTransaction()
        transaction.add(container, fragment as Fragment, tag)
        transaction.addToBackStack(tag)
        transaction.commit()
    }
}

call:

 activity!!.supportFragmentManager.showFragment<MenuFragment>(MenuFragment.TAG, R.id.container)

Answer 1

With Reflection provided that the fragment tag is the fully qualified name of the class provided using MenuFragment::class.java.name

private fun getFragment(fragmentTag: String, manager: FragmentManager, data: Any?): Fragment? {
    return manager.findFragmentByTag(fragmentTag) ?: getFragment(fragmentTag)
}

private fun getFragment(fragmentTag: String): Fragment? {
    val c = Class.forName(fragmentTag)
    return c.getMethod("newInstance").invoke(null) as Fragment?
}

Without Reflection

private fun getFragment(fragmentTag: String, manager: FragmentManager, data: Any?): Fragment? {
    return manager.findFragmentByTag(fragmentTag) ?: when (fragmentTag) {
        MenuFragment.TAG -> MenuFragment.newInstance()
        TagsFragment.TAG -> TagsFragment.newInstance()
        else -> null
    }
}

Answer 2

if I correctly understood a question, you can write extension function for FragmentManager like this

inline fun <reified T : Fragment> FragmentManager.getFragment(args: Bundle? = null): Fragment {
    val clazz = T::class.java
    return findFragmentByTag(clazz.name) ?: return (clazz.getConstructor().newInstance() as T).apply {
        args?.let { 
            it.classLoader = javaClass.classLoader
            arguments = args
        }
    }
}

end then use it, eg in activity

val frag = supportFragmentManager.getFragment<MyFragment>()

where MyFragment - is your fragment class