Unable to start activity componentinfo Nullpointerexception

Question

I am totaly new to java and i am trying to create a app that can send UDP (UDP part code from Google) to my visual basic program running on my pc. I dont use the textboxes yet, but its only sending a string of text when i press the button (atleast i want it to do that but i dont even get to that part because of the errors. I already searched almost whole google xD but i cant find anything that helps me (atleast what i understand). I know this is a question thats already asked so much times but i cant get wiser out of them sorry:P

Kere is the logcat list:

08-10 22:02:22.519: E/AndroidRuntime(16182): FATAL EXCEPTION: main
08-10 22:02:22.519: E/AndroidRuntime(16182): java.lang.RuntimeException: Unable to         start activity ComponentInfo{com.example.keetdoaldiek/com.example.keetdoaldiek.Keet}:                          java.lang.NullPointerException
08-10 22:02:22.519: E/AndroidRuntime(16182):    at    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2308)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.app.ActivityThread.access$600(ActivityThread.java:153)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.os.Handler.dispatchMessage(Handler.java:99)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.os.Looper.loop(Looper.java:137)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.app.ActivityThread.main(ActivityThread.java:5260)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  java.lang.reflect.Method.invokeNative(Native Method)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  java.lang.reflect.Method.invoke(Method.java:511)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  dalvik.system.NativeStart.main(Native Method)
08-10 22:02:22.519: E/AndroidRuntime(16182): Caused by: java.lang.NullPointerException
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  com.example.keetdoaldiek.Keet.senbutton(Keet.java:39)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  com.example.keetdoaldiek.Keet.onCreate(Keet.java:28)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.app.Activity.performCreate(Activity.java:5104)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at  android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
08-10 22:02:22.519: E/AndroidRuntime(16182):    at       android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2262)
08-10 22:02:22.519: E/AndroidRuntime(16182):    ... 11 more

This is my main.java

package com.example.keetdoaldiek;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;


import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;





public class Keet extends ActionBarActivity {

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

    sendbutton();

}





private void sendbutton() {
    Button messagebutton = (Button)findViewById(android.R.id.button1);

    messagebutton.setOnClickListener (new View.OnClickListener() {


        @Override
        public  void onClick(View v) {

             String messageStr = "Hello Android!";
                int server_port = 54372;
                try
                {
                    DatagramSocket s = new DatagramSocket();
                    InetAddress local = null;
                    local = InetAddress.getLocalHost();
                    int msg_length = messageStr.length();
                    byte[] message = messageStr.getBytes();
                    DatagramPacket p = new DatagramPacket(message, msg_length, local, server_port);
                    s.send(p);
                    s.close();
                    android.util.Log.w("UDP", "Works fine!");

                }
                catch (IOException e)
                {
                    e.printStackTrace();
                }
                catch (Exception e)
                {
                    android.util.Log.w("UDP", "Catched here.");
                e.printStackTrace();

                }



        }
    });
}





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

}

and this my manifest.

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

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="21" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >

    <activity
        android:name="Keet"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

I think its a variable that is nothing? but i don't know whitch one. i hope you guys can help me out with my problem.

Thanks,

Answer 1

You do not have the activity Keet declared correctly in the manifest. You can use either com.example.keetdoaldiek.Keet or .Keet as the android:name as follows:

<activity
    android:name="com.example.keetdoaldiek.Keet"
    android:label="@string/app_name" >
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

As per the official android documentation :

android:name The name of the class that implements the activity, a subclass of Activity. The attribute value should be a fully qualified class name (such as, "com.example.project.ExtracurricularActivity"). However, as a shorthand, if the first character of the name is a period (for example, ".ExtracurricularActivity"), it is appended to the package name specified in the element . Once you publish your application, you should not change this name (unless you've set android:exported="false").

There is no default. The name must be specified.

Answer 2

In your function sendbutton() change

Button messagebutton = (Button)findViewById(android.R.id.button1);

to

Button messagebutton = (Button)findViewById(R.id.button1);

and use

com.example.keetdoaldiek.R

This is because android.R is for general Android recources and com.example.keetdoaldiek.R is the generated index for your app.

Answer 3

Change

Button messagebutton = (Button)findViewById(android.R.id.button1);

to

Button messagebutton = (Button)findViewById(R.id.button1);

Second problem is your manifest is missing declaration to use internet which is required in this case: Put the below outside the application tag in the manifest.

<uses-permission android:name="android.permission.INTERNET" /> 
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>