Android App stürzt im Emulator

Question

Ich mache meine erste Android-App. Android Studio zeigt keinen Fehler im Code. Die App stürzt jedoch ab, sobald ich versuche, sie im Emulator zu starten. Ich verwende das eingebaute Nexus 5X API 23 für den Emulator. Bitte helfen Sie mir? Vielen Dank!

Hier ist mein Manifest-Datei:

<?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> 

Hier meine MainActivity.java Datei ist:

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(); 
     } 
    }); 
} 

} 

Hier ist die activity_main.xml Datei:

<?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> 

Hier ist t er Logcat:

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) 

Sie brauchen keinen FloatingActionButton, geschweige denn ein R.id.fab genannt, in Ihrem RelativeLayout. Sie verwenden die Datei activity_main.xml nicht in Ihrem Java-Code.

Answer 2

Sie setzen die setContentView(myLayout); Änderung dieses setContentView(R.layout.activity_main);