Android Studio emulator keeps stopping

Question

If i trying to run my app via the emulator it is keep stopping..how can i fix it ? here's my logcat:

2019-11-27 19:51:23.289 9621-9621/com.e.xmasplan E/AndroidRuntime: FATAL EXCEPTION: main
        Process: com.e.xmasplan, PID: 9621
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.e.xmasplan/com.e.xmasplan.MainActivity}: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.

Caused by: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.

    at com.e.xmasplan.MainActivity.onCreate(MainActivity.java:35) this line is blue printed.

this is line 35: userEmail = findViewById(R.id.email); the id in the xml file is email

heres the mainactivity xml file:

            `enter code here`<?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">


            <EditText
            android:id="@+id/username"
            android:layout_width="200dp"
            android:layout_height="55dp"
            android:ems="10"
            android:inputType="textPersonName"
            android:text="Username"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.578"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.193" />

            <EditText
            android:id="@+id/email"
            android:layout_width="200dp"
            android:layout_height="55dp"
            android:layout_marginBottom="380dp"
            android:ems="10"
            android:inputType="textEmailAddress"
            android:text="E-Mail"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.578"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/username"
            app:layout_constraintVertical_bias="0.109" />

            <EditText
            android:id="@+id/pw"
            android:layout_width="200dp"
            android:layout_height="55dp"
            android:ems="10"
            android:inputType="textPassword"
            android:text="Password"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.578"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/email"
            app:layout_constraintVertical_bias="0.029"
            tools:ignore="HardcodedText" />

            <EditText
            android:id="@+id/pw2"
            android:layout_width="200dp"
            android:layout_height="55dp"
            android:ems="10"
            android:inputType="textPassword"
            android:text="Confirm Password"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.578"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/pw"
            app:layout_constraintVertical_bias="0.037"
            tools:ignore="HardcodedText" />

            <Button
            android:id="@+id/regbtn"
            android:layout_width="167dp"
            android:layout_height="51dp"
            android:text="Register"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.577"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/pw2"
            app:layout_constraintVertical_bias="0.355" />

            <ProgressBar
            android:id="@+id/regProgressBar"
            style="?android:attr/progressBarStyle"
            android:layout_width="64dp"
            android:layout_height="44dp"
            app:layout_constraintBottom_toBottomOf="@+id/regbtn"
            app:layout_constraintEnd_toEndOf="@+id/regbtn"
            app:layout_constraintHorizontal_bias="0.514"
            app:layout_constraintStart_toStartOf="@+id/regbtn"
            app:layout_constraintTop_toTopOf="@+id/regbtn"
            app:layout_constraintVertical_bias="0.0" />

            <TextView
             android:id="@+id/signin"
             android:layout_width="311dp"
             android:layout_height="45dp"
             android:text="Already have an account ? Sign in here"
             android:textSize="18sp"
             app:layout_constraintBottom_toBottomOf="parent"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintHorizontal_bias="0.638"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toBottomOf="@+id/regbtn"
             app:layout_constraintVertical_bias="0.45" />

             </androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

Modify your Main Activity tag in the Manifest like following

<activity android:name=".MainActivity"
android:theme="@style/Theme.AppCompat" >

Answer 2

Go to the xml of your MainActivity and choose another theme, its located below the simulation right to the device that you simulate the code on, chose apptheme, or some kind of light theme