Error Java.Lang.NullPointer Exception on Android Twitter OAuth

Question

i have some problem, i want to make my application OAuth with twitter account

This is my Main.xml file

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:padding="@dimen/padding_medium"
        android:text="@string/hello_world"
        tools:context=".MainActivity" />

    <ImageButton
        android:id="@+id/btnTwitterConnect"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView1"
        android:layout_centerHorizontal="true"
        android:background="@drawable/standard_twitter"
        android:contentDescription="@string/twitter_btn_description"
        android:gravity="center" />

</RelativeLayout>

And this is my Main.java File

package com.test.twitteroauth;

import oauth.signpost.OAuth;
import oauth.signpost.commonshttp.CommonsHttpOAuthConsumer;
import oauth.signpost.commonshttp.CommonsHttpOAuthProvider;
import oauth.signpost.exception.OAuthCommunicationException;
import oauth.signpost.exception.OAuthExpectationFailedException;
import oauth.signpost.exception.OAuthMessageSignerException;
import oauth.signpost.exception.OAuthNotAuthorizedException;
import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.app.Dialog;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;



public class MainActivity extends Activity {

    private static final String CONSUMER_KEY = "CONSUMER KEY GOES HERE";
    private static final String CONSUMER_SECRET = "CONSUMER SECRET GOES HERE";

    private static String ACCESS_KEY = null;
    private static String ACCESS_SECRET = null;


    private static final String REQUEST_URL = "http://twitter.com/oauth/request_token";
    private static final String ACCESS_TOKEN_URL = "http://twitter.com/oauth/access_token";
    private static final String AUTH_URL = "http://twitter.com/oauth/authorize";
    private static final String CALLBACK_URL = "OauthTwitter://twitt";
    private static final String PREFERENCE_FILE = "twitter_oauth.prefs";

    private static CommonsHttpOAuthConsumer consumer = new CommonsHttpOAuthConsumer(CONSUMER_KEY, CONSUMER_SECRET);
    private static CommonsHttpOAuthProvider provider = new CommonsHttpOAuthProvider(REQUEST_URL, ACCESS_TOKEN_URL, AUTH_URL);


    @Override
    public void onCreate(Bundle savedInstanceState) {

        ImageButton btnTwitterConnect = (ImageButton) findViewById(R.id.btnTwitterConnect);
        btnTwitterConnect.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub

                try {
                     String authURL = provider.retrieveRequestToken(consumer, CALLBACK_URL);
                     Log.d("OAuthTwitter", authURL);
                     startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(authURL)));
                    } catch (OAuthMessageSignerException e) {
                        e.printStackTrace();
                    } catch (OAuthNotAuthorizedException e) {
                        e.printStackTrace();
                    } catch (OAuthExpectationFailedException e) {
                        e.printStackTrace();
                    } catch (OAuthCommunicationException e) {
                        e.printStackTrace();
                    }
            }
        });         
    }

        @Override
        public void onResume() {
            super.onResume();
        Uri uri = this.getIntent().getData();

        if (uri != null && uri.toString().startsWith(CALLBACK_URL)) {
            Log.d("OAuthTwitter", uri.toString());
        String verifier = uri.getQueryParameter(OAuth.OAUTH_VERIFIER);
            Log.d("OAuthTwitter", verifier);
        try {
        provider.retrieveAccessToken(consumer, verifier);
        ACCESS_KEY = consumer.getToken();
        ACCESS_SECRET = consumer.getTokenSecret();

        Log.d("OAuthTwitter", ACCESS_KEY);
        Log.d("OAuthTwitter", ACCESS_SECRET);

        } catch (OAuthMessageSignerException e) {
            e.printStackTrace();
        } catch (OAuthNotAuthorizedException e) {
            e.printStackTrace();
        } catch (OAuthExpectationFailedException e) {
            e.printStackTrace();
        } catch (OAuthCommunicationException e) {
            e.printStackTrace();
        }
       }
      }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }


}

I just followed the tutorial here: http://blog.copyninja.info/2010/09/android-oauth-authentication-with.html

But the android application is always Crashed

LogCat Details:

09-08 19:11:13.754: D/AndroidRuntime(566): Shutting down VM
09-08 19:11:13.754: W/dalvikvm(566): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
09-08 19:11:13.785: E/AndroidRuntime(566): FATAL EXCEPTION: main
09-08 19:11:13.785: E/AndroidRuntime(566): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.twitteroauth/com.test.twitteroauth.MainActivity}: java.lang.NullPointerException
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.os.Handler.dispatchMessage(Handler.java:99)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.os.Looper.loop(Looper.java:123)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.app.ActivityThread.main(ActivityThread.java:4627)
09-08 19:11:13.785: E/AndroidRuntime(566):  at java.lang.reflect.Method.invokeNative(Native Method)
09-08 19:11:13.785: E/AndroidRuntime(566):  at java.lang.reflect.Method.invoke(Method.java:521)
09-08 19:11:13.785: E/AndroidRuntime(566):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
09-08 19:11:13.785: E/AndroidRuntime(566):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
09-08 19:11:13.785: E/AndroidRuntime(566):  at dalvik.system.NativeStart.main(Native Method)
09-08 19:11:13.785: E/AndroidRuntime(566): Caused by: java.lang.NullPointerException
09-08 19:11:13.785: E/AndroidRuntime(566):  at com.test.twitteroauth.MainActivity.onCreate(MainActivity.java:44)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
09-08 19:11:13.785: E/AndroidRuntime(566):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
09-08 19:11:13.785: E/AndroidRuntime(566):  ... 11 more

I know it's caused by java.Lang.NullPointerException but where is the errors?

Thank you

(Android 2.2, Eclipse 3.7, Java JDK 1.7)

Answer 1

In addition to the setContentView(...) , you should call super.onCreate(savedInstanceState); above it, otherwise you'll end up with a SuperNotCalledException

@Override
public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(...);

   // ...

}

Answer 2

Please Add setcontentview(R.layout.main) line before ImageButton btnTwitterConnect = (ImageButton) findViewById(R.id.btnTwitterConnect); , it will solve your problem.

Answer 3

您需要调用setContentView(layoutID)并传递按钮所属的布局，然后再调用findViewById(viewId)