setContentView(R.Layout.Activity_Main)处的oncreate中出错；在Android Studio[副本]

Question

android studio中的货币转换器应用程序不停地停止，所以我对堆栈溢出进行了一点点搜索，为什么会出现这种情况，主要是因为一些小的错误，并且了解了如何检查堆栈跟踪，但是我没有能力解决这个问题。

在堆栈跟踪中，我看到错误位于OnCreat中的setContentView(r.layout.activity_main)。请帮我解决一下。我将在下面附加mainactivity.java和activity_main.xml。

mainactivity.java

 package edu.udayton.currencyconverter;

    import androidx.appcompat.app.AppCompatActivity;

    import android.app.Activity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.ArrayAdapter;
    import android.widget.Button;
    import android.widget.EditText;
    import android.widget.Spinner;
    import android.widget.Toast;

    public class MainActivity extends AppCompatActivity {

    Spinner sp1, sp2;
    EditText ed1;
    Button b1;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ed1 = findViewById(R.id.txtamount);
        sp1 = findViewById(R.id.spfrom);
        sp2 = findViewById(R.id.spto);
        b1  = findViewById(R.id.btn1);

        String[] from  = {"USD"};
        ArrayAdapter ad = new ArrayAdapter<String>( this,R.layout.support_simple_spinner_dropdown_item,from);
        sp1.setAdapter(ad);

        String[] to  = {"Euros","Canadian dollars"};
        ArrayAdapter ad1 = new ArrayAdapter<String>( this,R.layout.support_simple_spinner_dropdown_item,to);
        sp2.setAdapter(ad1);
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Double tot;
                Double amount = Double.parseDouble(ed1.getText().toString());
                if(sp1.getSelectedItem().toString() == "USD" && sp2.getSelectedItem().toString() == "Euros")
                {
                    tot = amount * 0.89;
                    Toast.makeText(getApplicationContext(), tot.toString(), Toast.LENGTH_LONG).show();

                }
                else if(sp1.getSelectedItem().toString() == "USD" && sp2.getSelectedItem().toString() == "Canadian dollars")
                {
                    tot = amount * 1.36;
                    Toast.makeText(getApplicationContext(), tot.toString(), Toast.LENGTH_LONG).show();
                }
            }
        });

    }
    }

activity_main.xml

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/currency_converter"
            android:textSize="30sp" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/enter_the_amount" />

        <EditText
            android:id="@+id/txtamount"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:autofillHints=""
            android:ems="10"
            android:hint="@string/amount_in_dollars"
            android:inputType="number" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/from" />
        <Spinner
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:id="@+id/spfrom"
            />

    </LinearLayout>
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/to" />

        <Spinner
            android:id="@+id/spto"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:spinnerMode="dropdown" />

    </LinearLayout>
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/convert"
            android:background="@color/colorPrimaryDark"
            android:id="@+id/btn1"
            />

    </LinearLayout>
</LinearLayout>

这是stacktrace堆栈跟踪

 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: edu.udayton.currencyconverter, PID: 17237
    java.lang.RuntimeException: Unable to start activity 
    ComponentInfo{edu.udayton.currencyconverter/edu.udayton.currencyconverter.MainActivity}: 
    java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this 
    activity.
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
        at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:696)
        at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:659)
        at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:552)
        at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:161)
        at edu.udayton.currencyconverter.MainActivity.onCreate(MainActivity.java:24)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6669) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

Answer 1

您需要在应用程序中使用AppCompact主题，因为您正在从MainActivity中删除AppCompactActivity。将应用程序主题更改为清单文件中的AppCompact主题。