如何在工具栏android kotlin上添加后退按钮

Question

I'm now to android, I am trying to add back button on toolbar using kotlin, tried almost every way posted on online, it just doesn't work at all, always crash for unknown reasons. Can anyone help?

class MainActivity : BaseActivity() {


  override fun getLayoutId(): Int {
      return  R.layout.activity_main
  }

  override fun initData() {
    super.initData()

    val testButton = findViewById<Button>(R.id.testButton)

    testButton.setOnClickListener{
        startActivity<RegistrationActivity>()
    }

  }

}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">


<include android:id="@+id/navBarView" layout="@layout/toolbar"/>

<Button
    android:id="@+id/testButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="92dp"
    android:layout_marginBottom="533dp"
    android:height="50dp"
    android:text="click me"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/navBarView" />


</androidx.constraintlayout.widget.ConstraintLayout>

// below is the toolbar xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.appcompat.widget.Toolbar 
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   android:id="@+id/toolbar"
   android:layout_width="match_parent"
   android:layout_height="?attr/actionBarSize"
   android:background="@color/white"
   app:titleTextColor="@color/white"
   app:popupTheme="@style/ThemeOverlay.AppCompat.ActionBar" >

<TextView
    android:layout_width="150dp"
    android:layout_height="wrap_content"
    android:src="@mipmap/title_view_image"
    android:layout_centerVertical="true"
    android:layout_gravity="center"
    android:gravity="center"
    android:text="Toolbar" />

</androidx.appcompat.widget.Toolbar>



class RegistrationActivity: BaseActivityWithBinding<ActivityRegistrationBinding>() {

   private lateinit var viewModel: UserViewModel

   override fun onCreated(savedInstanceState: Bundle?) {

      initToolbar()

      val factory = UserViewModelFactory()
      viewModel = ViewModelProviders.of(this,factory).get(UserViewModel::class.java)
      binding.myHandle = viewModel
      binding.lifecycleOwner = this

      viewModel.isStringEmpty.observe(this, Observer {
         if(it == true){
            showAlert()
         }
      })

}

fun initToolbar(){

    val toolbar = findViewById<Toolbar>(R.id.toolbar);
    setSupportActionBar(toolbar)
    supportActionBar?.apply {
        setDisplayShowHomeEnabled(false)
        setHomeAsUpIndicator(R.drawable.ic_baseline_keyboard_arrow_down_24)
    }

}

the back button doesn't show, I see different solutions online, and I tried them all, it doesn't work, can anyone check if I miss something or?

Answer 1

Toolbar xml code

<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#B0CAB2"
tools:context=".SecondActivity">

<androidx.appcompat.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?attr/colorPrimary"
    android:minHeight="?attr/actionBarSize"
    android:theme="?attr/actionBarTheme"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    android:elevation="4dp"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Second Activity"
    style="@style/TextAppearance.MaterialComponents.Headline3"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

style.xml

 <style name="AppTheme" parent="Theme.MaterialComponents.Light.NoActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
</style>

Activity.kt

 override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_second)

    // set toolbar as support action bar
    setSupportActionBar(toolbar)

    supportActionBar?.apply {
        title = "Toolbar Back Button Example"

        // show back button on toolbar
        // on back button press, it will navigate to parent activity
        setDisplayHomeAsUpEnabled(true)
        setDisplayShowHomeEnabled(true)
    }
}

Answer 2

setSupportActionBar(findViewById(R.id.toolbar))
// Get a support ActionBar corresponding to this toolbar and enable the Up button
supportActionBar?.setDisplayHomeAsUpEnabled(true)