Error redrawing com.google.android.gms.maps.MapFragment?

Question

Java

activity_main.xml :

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="24dp"
        android:onClick="showMap"
        android:text="Show map"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

activity_map.xml :

<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/map"
    android:name="com.google.android.gms.maps.MapFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

MainActivity :

public class MainActivity extends AppCompatActivity implements OnMapReadyCallback {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public void onBackPressed() {
        setContentView(R.layout.activity_main);
    }

    public void showMap(View view) {
        setContentView(R.layout.activity_map);
    }
}

Clicking on the "Show map" button opens the map. When the back button is pressed, activity_main is returned, but if the button is pressed again, the application crashes.
logcat:

2018-10-08 10:03:18.078 6618-6618/ru.webpi.pi.pavlovmap E/AndroidRuntime: FATAL EXCEPTION: main
    Process: ru.webpi.pi.pavlovmap, PID: 6618
    java.lang.IllegalStateException: Could not execute method for android:onClick
        at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:390)
        at android.view.View.performClick(View.java:6294)
        at android.view.View$PerformClick.run(View.java:24770)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:440)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385)
        at android.view.View.performClick(View.java:6294) 
        at android.view.View$PerformClick.run(View.java:24770) 
        at android.os.Handler.handleCallback(Handler.java:790) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6494) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:440) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 
     Caused by: android.view.InflateException: Binary XML file line #2: Binary XML file line #2: Error inflating class fragment
     Caused by: android.view.InflateException: Binary XML file line #2: Error inflating class fragment
     Caused by: java.lang.IllegalArgumentException: Binary XML file line #2: Duplicate id 0x7f070059, tag null, or parent id 0x1020002 with another fragment for com.google.android.gms.maps.MapFragment
        at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:3541)
        at android.app.FragmentController.onCreateView(FragmentController.java:98)
        at android.app.Activity.onCreateView(Activity.java:6219)
        at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:389)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:780)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
        at android.support.v7.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:469)
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
        at ru.webpi.pi.pavlovmap.MainActivity.showMap(MainActivity.java:35)
        at java.lang.reflect.Method.invoke(Native Method)
        at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385)
        at android.view.View.performClick(View.java:6294)
        at android.view.View$PerformClick.run(View.java:24770)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:440)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Answer 1

This is because setContentView() adds a new view to the existing hierarchy. When you call showMap() , the fragment is rendered, but you will get an error if you try to add it again, due to an id collision.
As a rule of thumb, setContentView() is called once per activity, fragment, or view lifecycle. This will avoid many strange bugs.
Read the documentation on how to work with fragments correctly.