Kotlin 25. How to refer to view objects in other xml in Kotlin

How to refer to view objects in other xml in Kotlin

For example, our activity_main.xmlwrites:

<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout 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:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <include
        layout="@layout/content_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <com.google.android.material.navigation.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/navigation_header_main"
        app:menu="@menu/activity_main_menu" />

</androidx.drawerlayout.widget.DrawerLayout>

The here activity_main.xmlconsists of two parts: content_mainthe layout of and nav_viewthe sidebar of the .

content_main.xmlas follows:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.appbar.AppBarLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light">
            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="horizontal"
                android:gravity="center_vertical">
                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@string/tool_bar"
                    android:textColor="#FFFFFF"
                    style="@style/TextAppearance.AppCompat.Widget.ActionBar.Title"/>
            </LinearLayout>
        </androidx.appcompat.widget.Toolbar>

    </com.google.android.material.appbar.AppBarLayout>


    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <Button
            android:id="@+id/buttonAdd"
            android:layout_width="88dp"
            android:layout_height="48dp"
            android:text="@string/add"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toEndOf="@+id/menuEditText"
            app:layout_constraintTop_toTopOf="parent" />

        <EditText
            android:id="@+id/menuEditText"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="textPersonName"
            android:text="@string/menu_name"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toStartOf="@+id/buttonAdd"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>

</LinearLayout>

That is, contain an EditText and a Button.

So the question is, how to MainActivity.ktuse buttonAddthis button in ?

It's actually very simple, first, we need to build.gradle (Module)add in 'kotlin-android-extensions':

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
    id 'kotlin-android-extensions'
}

Then, in MainActivity.kt, when we use the layout id name to get content_main.xmlthe view object, the system will import it import kotlinx.android.synthetic.main.content_main.*, so that we can directly get the View objects of other Layouts.