当我按回来时导航片段的问题

Question

Have a fragment in which I display the recyclerView list. When I click on a list item in MainActivity I call the method:

fun FragmentActivity?.replaceFragment(fragment: Fragment): Boolean {
    if (this == null) return false
    try {
        supportFragmentManager?.beginTransaction()?.replace(
            R.id.container, fragment,
            fragment.createTagName()
        )?.commit()
    } catch (ignored: IllegalStateException) {
        return false
    }
    return true
}

After this I press the system back button and I have a duplicate list.

Also i have in my MainActivity next fun:

 override fun onBackPressed() {
        val onBackPressListener = currentFragmentInContainer() as? OnBackPressListener
        if (onBackPressListener?.onBackPress() != true) {
            super.onBackPressed()
        }
    }

Answer 1

The issue is you have not added the current fragment to the back stack. In order to get to the starting point, you have to mark the fragment. addToBackStack(tag:String) will help you to do that.

Code:

fun FragmentActivity?.replaceFragment(fragment: Fragment): Boolean {
    if (this == null) return false
    try {
        supportFragmentManager?.beginTransaction()?.replace(
            R.id.container, fragment,
            fragment.createTagName()
        ).addToBackStack(fragment.createTagName())?.commit()
    } catch (ignored: IllegalStateException) {
        return false
    }
    return true
}

Here is the documentation about the method : addToBackStack