我正在学习如何开发应用程序，但我不知道为什么我的应用程序崩溃了

Question

2021-04-01 00:33:47.674 19798-19798/? E/Zygote: isWhitelistProcess - Process is Whitelisted    
2021-04-01 00:33:47.676 19798-19798/? E/Zygote: accessInfo : 1    
2021-04-01 00:33:47.733 19798-19798/? E/programingbasi: Unknown bits set in runtime_flags: 0x8000

这些在 logcat-error 上（我不确定它是否对您回答有帮助）

由于我只编辑了下面的java代码和xml代码，所以我只添加了这些代码

Java 代码 '''

package com.song.androidprogramingbasic;
import android.content.DialogInterface;
import android.content.Intent;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    MediaPlayer mp = MediaPlayer.create(this, R.raw.alarm_sound);

    @Override
    protected void onCreate(Bundle savedInstanceState){ /* 가장 먼저 실행되는 함수*/
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView title = (TextView) findViewById(R.id.first_screen);
        title.setText(R.string.Hello_INU);
    }

    public void Button1(View view){
        Intent intent = new Intent(MainActivity.this, Button1Activity.class);
        startActivity(intent); /*Intent객체를 받아서, intent객체의 정보로 뭔가를 한다고 함*/
    }

    public void Button2(View view){
        Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("tel:010-1234-5678"));
        startActivity(intent); /*Intent객체를 받아서, intent객체의 정보로 뭔가를 한다고 함*/
    }

    public void alert_Dialog(View view){
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setMessage(R.string.button4_text);
        builder.setTitle(R.string.button4_title);
        builder.setPositiveButton(R.string.button4_dismiss, new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });

        AlertDialog alert_dialog = builder.create();
        alert_dialog.show();
    }

    public void alarm_sound(View view){
        mp.seekTo(0);
        mp.start();
    }

    public void on_Long_Click(View view){

        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setMessage(R.string.button8_text);
        builder.setTitle(R.string.button8_title);
        builder.setPositiveButton(R.string.button8_dismiss, new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });
        AlertDialog alert_dialog = builder.create();
        alert_dialog.show();
    }
}

'''

mxl 代码

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical">

    <TextView
        android:id="@+id/first_screen"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textStyle="italic"
        android:text="@string/first_screen"
        />

    <EditText
        android:id="@+id/first_screen_EditText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:autofillHints="@string/first_screen_edittext"
        android:hint="@string/first_screen_edittext"
        android:singleLine="false"
        android:inputType="text"
        />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <Button
            android:id="@+id/button1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="Button1"
            android:text="@string/button1" />

        <Button
            android:id="@+id/button2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="Button2"
            android:text="@string/button2" />
        <Button
            android:id="@+id/button3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/button3" />
        <Button
            android:id="@+id/button4"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/button4"
            android:onClick="alert_Dialog"/>
        <Button
            android:id="@+id/button5"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/button5" />
        <Button
            android:id="@+id/button6"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/button6" />
        <Button
            android:id="@+id/button7"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="alarm_sound"
            android:text="@string/button7" />
        <Button
            android:id="@+id/button8"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="on_Long_Click"
            android:longClickable="true"
            android:focusable="true"
            android:text="@string/button8" />
        <ImageView
            android:id="@+id/first_screen_icon"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:layout_marginLeft="50dp"
            android:src="@mipmap/incheon_national_university"
            android:adjustViewBounds="true"
            android:layout_marginStart="50dp"
            android:contentDescription="@mipmap/incheon_national_university" />
    </LinearLayout>
</LinearLayout>

Answer 1

是的，因为您在创建到 MediaPalyer.create(Context,resID) 的 Activity 之前添加了一个 null Context

尝试在 onCreate 方法中初始化 MediaPlayer，如下所示：

    MediaPlayer mp;
    
    @Override
    protected void onCreate(Bundle savedInstanceState){ /* 가장 먼저 실행되는 함수*/
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView title = (TextView) findViewById(R.id.first_screen);
        title.setText("R.string.Hello_INU");
        mp=MediaPlayer.create(this, R.raw.alarm_sound);

    }