エラーが発生しましたjava.lang.RuntimeException：アクティビティを開始できませんComponentInfo

Question

リニアレイアウトの使い方を学習しています。新しいレイアウトリソースファイルを作成し、ボタンとテキストをドラッグしてプロパティを調整しました。 API 16. と仮想デバイス上で動作しているしようとしたときにアプリがクラッシュした私は、次のソリューションを試みたが、うまくいきませんでした：

• 私は私は私のアプリのテーマを変更した15
• にAPIを変更しましたここでHolo.light.DarkActionBar

はlogcatです：

06-14 20:56:20.692 1281-1281/? D/dalvikvm: Late-enabling CheckJNI 
06-14 20:56:20.728 1281-1287/? D/dalvikvm: Debugger has detached; object registry had 1 entries 
06-14 20:56:20.796 1281-1281/? W/dalvikvm: VFY: unable to find class referenced in signature (Landroid/view/SearchEvent;) 
06-14 20:56:20.800 1281-1281/? I/dalvikvm: Could not find method android.view.Window$Callback.onSearchRequested, referenced from method android.support.v7.view.WindowCallbackWrapper.onSearchRequested 
06-14 20:56:20.800 1281-1281/? W/dalvikvm: VFY: unable to resolve interface method 18815: Landroid/view/Window$Callback;.onSearchRequested (Landroid/view/SearchEvent;)Z 
06-14 20:56:20.800 1281-1281/? D/dalvikvm: VFY: replacing opcode 0x72 at 0x0002 
06-14 20:56:20.800 1281-1281/? I/dalvikvm: Could not find method android.view.Window$Callback.onWindowStartingActionMode, referenced from method android.support.v7.view.WindowCallbackWrapper.onWindowStartingActionMode 
06-14 20:56:20.800 1281-1281/? W/dalvikvm: VFY: unable to resolve interface method 18819: Landroid/view/Window$Callback;.onWindowStartingActionMode (Landroid/view/ActionMode$Callback;I)Landroid/view/ActionMode; 
06-14 20:56:20.800 1281-1281/? D/dalvikvm: VFY: replacing opcode 0x72 at 0x0002 
06-14 20:56:20.816 1281-1281/? D/AndroidRuntime: Shutting down VM 
06-14 20:56:20.816 1281-1281/? W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xa6253288) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime: FATAL EXCEPTION: main 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.shubhendu.linearlayoutexperiments/com.example.shubhendu.linearlayoutexperiments.MainActivity}: java.lang.NullPointerException 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.access$600(ActivityThread.java:130) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:99) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:137) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:4745) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:511) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime: Caused by: java.lang.NullPointerException 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at com.example.shubhendu.linearlayoutexperiments.MainActivity.onCreate(MainActivity.java:22) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.Activity.performCreate(Activity.java:5008) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.access$600(ActivityThread.java:130)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:99)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:137)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:4745)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:511)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)  
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method)  
06-14 20:56:22.640 1281-1281/? I/Process: Sending signal. PID: 1281 SIG: 9 

マイMainActivity.java：

package com.example.shubhendu.linearlayoutexperiments; 

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.view.Menu; 
import android.view.MenuItem; 

public class MainActivity extends AppCompatActivity { 

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

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_main, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 
} 

そして、私のlinear_experiment.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="vertical" android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <LinearLayout 
     android:orientation="horizontal" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center_horizontal" 
     android:layout_weight=".5" 
     android:gravity="center_horizontal"> 

     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="New Button" 
      android:id="@+id/button" /> 

     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="New Button" 
      android:id="@+id/button2" /> 
    </LinearLayout> 

    <LinearLayout 
     android:orientation="vertical" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center_horizontal" 
     android:layout_weight="0.5"> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="New Text" 
      android:id="@+id/textView" 
      android:layout_gravity="center_horizontal" 
      android:layout_marginTop="20dp" /> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="New Text" 
      android:id="@+id/textView2" 
      android:layout_gravity="center_horizontal" 
      android:layout_marginTop="20dp" /> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="New Text" 
      android:id="@+id/textView3" 
      android:layout_gravity="center_horizontal" 
      android:layout_marginTop="20dp" /> 
    </LinearLayout> 
</LinearLayout> 

Answer 1

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

Toolbarですかandroid:id="@+id/toolbar"があります。レイアウトでは何もありません。

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 

FloatingActionButtonですかandroid:id="@+id/fab"があります。レイアウトでは何もありません。

Answer 2

「fab」という名前のボタンがないようです。その名前で使用しようとしているボタンをこれに変更する必要があります。 android：id = "@ + id/fab" />