Android_Review_1_findViewById

Kotlin means no more findViewById, haha

從小被嫌到大的 findViewById，歷經 ButterKnife 和 Data Binding 的改革， 在 Kotlin 又更上一層樓，只要 import layout 之後就可以直接用裡面全部的元件，不須任何宣告。

no more dummy code as below:

classNmae: Activity(){

    
      var btn: Button ? = null

      override onCreate(){

          val btn = findviewById(R.id.xoxoxox)

      }


}

1. go to module level build gradle, and then apply the plugins as same as following hightlight top 3 plugins.

2. code for BFragment class in kotlin.

    package com.katepatty.pk_downloader
   
    import android.os.Bundle
    import androidx.fragment.app.Fragment
    import android.view.LayoutInflater
    import android.view.View
    import android.view.ViewGroup
    import androidx.navigation.findNavController
    
    // import module
    
    import kotlinx.android.synthetic.main.fragment_b.*
   
   
    class BFragment : Fragment() {
   
        // kotlin 元件免宣告定義
        //var btn: Button? = null
   
        override fun onCreateView(
            inflater: LayoutInflater, container: ViewGroup?,
            savedInstanceState: Bundle?
        ): View? {
            // Inflate the layout for this fragment
            return inflater.inflate(R.layout.fragment_a, container, false)
   
            // no more findviewbyid in Kotlin
            //btn = (Button) findViewById(R.id.navigate_btn);
   
        }
        override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            super.onViewCreated(view, savedInstanceState)
   
            // add this code to do a action-trigger
            //val navController = findNavController(MainActivity, R.id.AFragment)
            //val navHostFragment = supportFragmentManager.findFragmentById(R.id.AFragment) as NavHostFragment
            //val navController = navHostFragment.navController
   
            //btn!!.setOnClickListener { navController.navigate(R.id.action_AFragment_to_BFragment) }
   
                                   // this id can be both of the dest-fragment id or action id
            // call btn id directly                       
            navigate_btn!!.setOnClickListener {it.findNavController().navigate(R.id.BFragment)}
   
        }
   
    }
   

3. layout for fragment_b.xml

                    <?xml version="1.0" encoding="utf-8"?>
                    
                    <FrameLayout
                        xmlns:android="http://schemas.android.com/apk/res/android"
                        android:layout_width="match_parent"
                        android:layout_height="match_parent">
   
   
                        <ImageButton
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:src="@drawable/circle"/>
   
                        <Button
                            android:id="@+id/navigate_btn"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:layout_gravity="center_horizontal"
                            android:text="go to => 2" />
   
                        <TextView
                            android:id="@+id/content_text"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:layout_gravity="center"
                            android:text="Welcome to Kate ＆ Pattys Image Castle" />
   
   
                    </FrameLayout>
   

4. prepare for before mentioned step (2) & (3)

• upper object 's layout id

• import kotlinx.android.synthetic.main.LayoutId.*

• layout id

• object id