Android kotlin fragment technology point

1.Fragment Definition

Fragment It's something that can be embedded in Activity In the middle of UI fragment , It allows programs to make more rational use of screen space , It can be understood as a mini Activity

2.Fragment Declaration period

onAttach()->onCreate()->onCreateView()->onActivityCreate()->onStart()->onResume()->onPause()->onStop()->onDestroyView()->onDestroy()->onDetach()

• onAttach(): When Fragment and Activity Call... When establishing an association
• onCreateView(): by Fragment When creating a view, call
• onActivityCreate(): Ensure that Fragment The associated Activity Callback after creation
• onDestroyView(): When and Fragment Called when the associated view is removed
• onDetach(): When Fragment and Activity Called when disassociated

3.Fragment Use

<fragment android:id="@+id/leftFragment"
          android:layout_width="0dp"
          android:layout_height="match_parent"
          android:layout_weight="1"
          android:name="com.test.kotlin_test.fragment.LeftFragment"
/>

adopt fragment Labels are added directly to the layout file , adopt name To specify which fragment, This method is directly fixed in the layout file , If it needs to be replaced, it is not very convenient .

private fun replaceFragment(rightFragment: Fragment) {
    
    val fragmentManager = supportFragmentManager
    val transaction = fragmentManager.beginTransaction()
    transaction.apply {
    
        replace(R.id.rightFragment, rightFragment)
        addToBackStack(null)
        commit()
    }
}

Dynamic replacement and addition Fragment, adopt addToBackStack Method can add transactions to the return stack , Click back to return to the previous one fragment The state of , You need to pass a name to describe the status of the return stack , According to the demand, if there are no special requirements, you can send null

4.Fragment and Activity Interaction

val fragmentActivity = activity as FragmentActivity

stay Fragment Pass through getActivity Method gets the containing Activity example , After forced rotation, it can be executed Activity The way inside

val leftFragment = supportFragmentManager.findFragmentById(R.id.leftFragment) as LeftFragment

stay Activity perform findFragmentById You can get the loaded fragment example , It can be easily executed fragment The way inside

5.Activity towards Fragment Pass parameters

// adopt Bundle Pass parameters , And put bundle Set to argument
val bundle=Bundle()
bundle.putString(LeftFragment.KEY_PARAM,"test")
rightFragment.arguments=bundle

// stay Fragment Of onCreate Method to get parameters 
   override fun onCreate(savedInstanceState: Bundle?) {
    
        super.onCreate(savedInstanceState)
        val param = arguments?.getString(KEY_PARAM)
    }

Fragment There is one argument Parameters , You can use this to give Fragment Pass parameters .

6. Dynamic loading layout

Previously, I learned about dynamic loading Fragment The way , The program can also load the layout file according to the resolution of the device or the size of the screen , To achieve this, you need to understand qualifiers

large qualifiers

newly build res below layout-large Folder , Create a new layout file with the same name under this file activity_fragment.xml, This one contains left and right Fragment,layout inside activity_fragment.xml Contains a Fragment.

Deploying the program to the flat-panel simulator shows layout-large The layout file inside

Deploying the program on the mobile phone shows layout The layout file inside

smallest-width Minimum width qualifier

Specify a minimum value for the width of the screen , Then take this minimum value as the critical value

You can specify different layout files under different width resolutions , Achieve perfect layout file adaptation

layout-sw500dp

layout-sw400dp