Error from the main activity when running application

Question

I have been following Android Development tutorials online but when I run the app on the emulator it closes due to errors.

I Googled the first error to no avail.But looking through the rest of the log cat I noticed it was throwing errors from the main activity.I think it may be a problem with my manifest file but I'm not sure what exactly.

My package name is com.example.androidtutorials.

Could someone enlighten me as to what I have done incorrectly in following the tutorial.My manifest file is as follows:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.androidtutorials"
    android:versionCode="1"
    android:versionName="1.0" >


    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.androidtutorials.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

        <activity
            android:name=".Numbers"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.NUMBERS" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

        <activity
            android:name=".InternalStorage"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.INTERNALSTORAGE" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

        <activity
            android:name=".Reading"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.READING" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

        <activity
            android:name=".Menu"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MENU" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

         <activity
            android:name=".SaveToSD"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.SAVETOSD" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>  

    </application>

</manifest>

Log cat:

 09-20 17:22:58.802: E/Trace(799): error opening trace file: No such file or directory (2)
    09-20 17:23:02.662: D/AndroidRuntime(799): Shutting down VM
    09-20 17:23:02.662: W/dalvikvm(799): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
    09-20 17:23:02.707: E/AndroidRuntime(799): FATAL EXCEPTION: main
    09-20 17:23:02.707: E/AndroidRuntime(799): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.androidtutorials/com.example.androidtutorials.MainActivity}: java.lang.NullPointerException
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.os.Handler.dispatchMessage(Handler.java:99)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.os.Looper.loop(Looper.java:137)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.ActivityThread.main(ActivityThread.java:5041)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at java.lang.reflect.Method.invokeNative(Native Method)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at java.lang.reflect.Method.invoke(Method.java:511)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at dalvik.system.NativeStart.main(Native Method)
    09-20 17:23:02.707: E/AndroidRuntime(799): Caused by: java.lang.NullPointerException
    09-20 17:23:02.707: E/AndroidRuntime(799):  at com.example.androidtutorials.MainActivity.onCreate(MainActivity.java:27)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.Activity.performCreate(Activity.java:5104)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
    09-20 17:23:02.707: E/AndroidRuntime(799):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
    09-20 17:23:02.707: E/AndroidRuntime(799):  ... 11 more
    09-20 17:27:43.197: I/Process(799): Sending signal. PID: 799 SIG: 9
    09-20 17:27:45.187: D/AndroidRuntime(858): Shutting down VM
    09-20 17:27:45.187: W/dalvikvm(858): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
    09-20 17:27:45.207: E/AndroidRuntime(858): FATAL EXCEPTION: main
    09-20 17:27:45.207: E/AndroidRuntime(858): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.androidtutorials/com.example.androidtutorials.MainActivity}: java.lang.NullPointerException
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.os.Handler.dispatchMessage(Handler.java:99)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.os.Looper.loop(Looper.java:137)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.ActivityThread.main(ActivityThread.java:5041)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at java.lang.reflect.Method.invokeNative(Native Method)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at java.lang.reflect.Method.invoke(Method.java:511)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at dalvik.system.NativeStart.main(Native Method)
    09-20 17:27:45.207: E/AndroidRuntime(858): Caused by: java.lang.NullPointerException
    09-20 17:27:45.207: E/AndroidRuntime(858):  at com.example.androidtutorials.MainActivity.onCreate(MainActivity.java:27)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.Activity.performCreate(Activity.java:5104)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
    09-20 17:27:45.207: E/AndroidRuntime(858):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
    09-20 17:27:45.207: E/AndroidRuntime(858):  ... 11 more
    09-20 17:27:48.847: I/Process(858): Sending signal. PID: 858 SIG: 9

My onCreate method from the main class:

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        width = (Button)findViewById(R.id.button1);
        height = (Button)findViewById(R.id.button2);
        calc = (Button)findViewById(R.id.button3);
        area = (TextView)findViewById(R.id.textView1);

        width.setOnClickListener(this);
        height.setOnClickListener(this);
        calc.setOnClickListener(this);
    }

_errors from the main activity_ Then that is what you should post here... — Sotirios Delimanolis, Sep 20 '13 at 17:42
Just the `onCreate()` not the whole class, unless there is something else you think is particularly relevant. — codeMagic, Sep 20 '13 at 17:52
I have seven Java classes but from the lo cat it seems to be the main so I'll post that. — Brian Var, Sep 20 '13 at 17:53
What is at line 27? And make sure that all of those `id`s exist in `activity_main.xml` — codeMagic, Sep 20 '13 at 17:57
This is at line #27 width.setOnClickListener(this); in the onCreate() — Brian Var, Sep 20 '13 at 18:01
thanks @codeMagic I just checked my xml and the buttons were uppercase 'b' so maybe this was the problem.Running it now to check. — Brian Var, Sep 20 '13 at 18:06
That would definitely cause the problem. Make sure to double check all of your `View`s so you don't have other `NPE`s — codeMagic, Sep 20 '13 at 18:07

score 1 · Accepted Answer · answered Sep 20 '13 at 18:03

Since this line is giving you the NPE

width.setOnClickListener(this)

then width must be null. This means that button1 is not an id of a Button in your layout file activity_main.xml.

Check your layout file that you have a Button like

<Button
    android:id="@+id/button1"
    .../>

If you feel you have this then try cleaning your project

Project --> Clean..

and please post that xml file if that doesn't fix your problem. But I'm sure that you will find you don't.

Sorted now.The problem was with the ids as you stated in your answer.The button name was uppercase Button. — Brian Var, Sep 20 '13 at 18:19

Error from the main activity when running application

1 Answers1