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

转到您的 MainActivity 的 xml 并选择另一个主题，它位于您模拟代码的设备右侧的模拟下方，选择了 apptheme 或某种浅色主题