에뮬레이터에서 Android 앱이 계속 충돌합니다.

Question

첫 번째 Android 앱을 만들고 있습니다. Android Studio에서 코드에 오류가 표시되지 않습니다. 그러나 에뮬레이터에서 앱을 실행하자마자 앱이 계속 충돌합니다. 에뮬레이터 용으로 내장 Nexus 5X API 23을 사용하고 있습니다. 도와주세요. 감사합니다.

<?xml version="1.0" encoding="utf-8"?> 
<android.support.design.widget.CoordinatorLayout  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:fitsSystemWindows="true" 
tools:context="com.example.admin.coursebrowser.MainActivity"> 

<android.support.design.widget.AppBarLayout 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:theme="@style/AppTheme.AppBarOverlay"> 

    <android.support.v7.widget.Toolbar 
     android:id="@+id/toolbar" 
     android:layout_width="match_parent" 
     android:layout_height="?attr/actionBarSize" 
     android:background="?attr/colorPrimary" 
     app:popupTheme="@style/AppTheme.PopupOverlay" /> 

</android.support.design.widget.AppBarLayout> 

<include layout="@layout/content_main" /> 

<android.support.design.widget.FloatingActionButton 
    android:id="@+id/fab" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_gravity="bottom|end" 
    android:layout_margin="@dimen/fab_margin" 
    android:src="@android:drawable/ic_dialog_email" /> 

</android.support.design.widget.CoordinatorLayout> 

: 여기

package com.example.admin.coursebrowser; 

import android.os.Bundle; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.widget.RelativeLayout; 
import android.widget.Button; 
import android.graphics.Color; 

public class MainActivity extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    RelativeLayout myLayout= new RelativeLayout(this); 
    myLayout.setBackgroundColor(Color.CYAN); 
    Button redButton= new Button(this); 
    redButton.setText("Click Me"); 
    redButton.setBackgroundColor(Color.RED); 
    myLayout.addView(redButton); 
    setContentView(myLayout); 

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
    fab.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
        .setAction("Action", null).show(); 
     } 
    }); 
} 

} 

가 activity_main.xml 파일입니다

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="com.example.admin.coursebrowser"> 

<application 
    android:allowBackup="true" 
    android:icon="@mipmap/ic_launcher" 
    android:label="@string/app_name" 
    android:supportsRtl="true" 
    android:theme="@style/AppTheme"> 
    <activity 
     android:name=".MainActivity" 
     android:label="@string/title_activity_main" 
     android:theme="@style/AppTheme.NoActionBar"> 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
</application> 

여기

내 MainActivity.java 파일입니다 : 여기

내 매니페스트 파일입니다

여기 있습니다. 그는 로그 캣 : 당신은 FloatingActionButton가 커녕 한 당신의 RelativeLayout에, R.id.fab 이름없는

08-10 15:09:23.291 3442-3442/com.example.admin.coursebrowser E/AndroidRuntime: FATAL EXCEPTION: main 
    Process: com.example.admin.coursebrowser, PID: 3442 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.admin.coursebrowser/com.example.admin.coursebrowser.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:148) 
     at android.app.ActivityThread.main(ActivityThread.java:5417) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
     at com.example.admin.coursebrowser.MainActivity.onCreate(MainActivity.java:30) 
     at android.app.Activity.performCreate(Activity.java:6237) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:148) 
     at android.app.ActivityThread.main(ActivityThread.java:5417) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Answer 1

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.example.admin.coursebrowser.MainActivity.onCreate(MainActivity.java:30) 

. Java 코드에서 activity_main.xml 파일을 사용하고 있지 않습니다.

Answer 2

당신은 setContentView(R.layout.activity_main);