无法启动活动ComponentInfo：java.lang.NullPointerException

Question

我已经搜索了这个错误，并找到了许多解决方案，但我无法解决这个问题，因为我是Android的初学者

package ***.***.greytrix.test;

import android.app.LauncherActivity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.os.AsyncTask;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;    
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;

import android.widget.TextView;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.gcm.GoogleCloudMessaging;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

import android.webkit.CookieManager;

public class MainActivity extends ActionBarActivity {


    private WebView mWebView;
    private  Context context;

    public static final String EXTRA_MESSAGE = "message";
    public static final String PROPERTY_REG_ID = "registration_id";
    private static final String PROPERTY_APP_VERSION = "appVersion";
    private final static int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
    // please enter your sender id
    String SENDER_ID = "11111111";

    static final String TAG = "Pocket ";
    GoogleCloudMessaging gcm;

    TextView mDisplay;

    String regid;
    String fileurl="https://neel.test.com/";
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);


        setContentView(R.layout.activity_main);
        context = getApplicationContext();

        if(checkPlayServices()){
            gcm = GoogleCloudMessaging.getInstance(this);
           regid = getRegistrationId(context);


            //For Testing Purpose
              new RegisterBackground().execute();
        }


        Bundle extras = getIntent().getExtras();
        String url;

        if (extras != null) {

            url = extras.getString("url");

            mWebView = (WebView) findViewById(R.id.activity_main_webview);

            mWebView.getSettings().setJavaScriptEnabled(true);
            mWebView.getSettings().setDomStorageEnabled(true);
            mWebView.getSettings().setDatabaseEnabled(true);

            if (extras.getString("url").isEmpty()) {
                mWebView.loadUrl("https://neel.test.com/");
            } else {
                mWebView.loadUrl(url);
            }
            mWebView.setWebViewClient(new MyAppWebViewClient());

        } else {

            mWebView = (WebView) findViewById(R.id.activity_main_webview);

            WebSettings webSettings = mWebView.getSettings();
            webSettings.setJavaScriptEnabled(true);
            webSettings.setDomStorageEnabled(true);
            webSettings.setDatabaseEnabled(true);

             fileurl = ReadFile();

            if (fileurl == "") {
                fileurl="https://neel.test.com/";
                mWebView.loadUrl("https://neel.test.com/");
            } else {
                mWebView.loadUrl(fileurl);
            }
            mWebView.setWebViewClient(new MyAppWebViewClient());

        }

    }

    private String ReadFile() {

        String aBuffer = "";

        try {
            File myFile = new File(getFilesDir() + "/mysdfile.txt");
            if (myFile.exists()) {
                FileInputStream fIn = new FileInputStream(myFile);
                BufferedReader myReader = new BufferedReader(
                        new InputStreamReader(fIn));
                String aDataRow = "";

                while ((aDataRow = myReader.readLine()) != null) {
                    aBuffer += aDataRow + "\n";
                }
                myReader.close();
            }

        } catch (Exception e) {
            Toast.makeText(getBaseContext(), e.getMessage(),
                    Toast.LENGTH_SHORT).show();
        }

        return aBuffer.trim();
    }


    @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.SetURL) {

            Intent nextscreen = new Intent(PayrollApplication.getContext(), SecondScreenActivity.class);
            startActivity(nextscreen);

            //setContentView(R.layout.seturl);

            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onBackPressed() {
        if (mWebView.canGoBack()) {
            mWebView.goBack();
        } else {
            super.onBackPressed();
        }
    }
    @Override
    protected void onResume(){
        super.onResume();
        checkPlayServices();
    }

    //New Code developed by Nilesh Gajare on 10th July 2015

    class RegisterBackground extends AsyncTask<String,String,String> {

        @Override
        protected String doInBackground(String... arg0) {
            // TODO Auto-generated method stub
            String msg = "";
            try {
                if (gcm == null) {
                    gcm = GoogleCloudMessaging.getInstance(context);
                }
                regid = gcm.register(SENDER_ID);
                msg = "Device registered, registration ID=" + regid;
                Log.d("111", msg);
                sendRegistrationIdToBackend();

                // Persist the regID - no need to register again.
               storeRegistrationId(context, regid);
            } catch (IOException ex) {
                msg = "Error :" + ex.getMessage();
            }
            return msg;
        }

        @Override
        protected void onPostExecute(String msg) {
            //mDisplay.append(msg + "\n");

        }
        private void sendRegistrationIdToBackend() {
            // Set Server URL for Storing Android Device Registration ID.

            String CompanyCode= getCookie(fileurl,"CompanyId");
            String UserName= getCookie(fileurl,"UserName");
            String Password= getCookie(fileurl,"Password");

            String url = "https://neel.test.com//api/v1.0/SaveAndroidRegId?RegId="+regid+"&CompanyId="+CompanyCode+"&UserName="+UserName+"&Password="+Password ;   

            try {
                HttpResponse httpResponse = httpClient.execute(httpPost);
               Log.i(TAG,httpResponse.getStatusLine().toString());
                Log.i(TAG,httpResponse.getEntity().toString());

            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }



        }

        private void storeRegistrationId(Context context, String regId) {
            final SharedPreferences prefs = getGCMPreferences(context);
            int appVersion = getAppVersion(context);
            Log.i(TAG, "Saving regId on app version " + appVersion);
            SharedPreferences.Editor editor = prefs.edit();
            editor.putString(PROPERTY_REG_ID, regId);
            editor.putInt(PROPERTY_APP_VERSION, appVersion);
            editor.commit();
        }
    }

    private boolean checkPlayServices() {
        int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
        if (resultCode != ConnectionResult.SUCCESS) {
            if (GooglePlayServicesUtil.isUserRecoverableError(resultCode)) {
                GooglePlayServicesUtil.getErrorDialog(resultCode, this,
                        PLAY_SERVICES_RESOLUTION_REQUEST).show();
            } else {
                Log.i(TAG, "This device is not supported.");
                finish();
            }
            return false;
        }
        return true;
    }
    private String getRegistrationId(Context context) {
        final SharedPreferences prefs = getGCMPreferences(context);

        String registrationId = prefs.getString(PROPERTY_REG_ID, "");


        if (registrationId.isEmpty()) {
            Log.i(TAG, "Registration not found.");
            return "";
        }

        int registeredVersion = prefs.getInt(PROPERTY_APP_VERSION, Integer.MIN_VALUE);
        int currentVersion = getAppVersion(context);
        if (registeredVersion != currentVersion) {
            Log.i(TAG, "App version changed.");
            return "";
        }
        return registrationId;
    }

    private SharedPreferences getGCMPreferences(Context context) {

        return getSharedPreferences(MainActivity.class.getSimpleName(),
                Context.MODE_PRIVATE);
    }

    private static int getAppVersion(Context context) {
        try {
            PackageInfo packageInfo = context.getPackageManager()
                    .getPackageInfo(context.getPackageName(), 0);
            return packageInfo.versionCode;
        } catch (PackageManager.NameNotFoundException e) {
            // should never happen
            throw new RuntimeException("Could not get package name: " + e);
        }
    }

    public String getCookie(String siteName,String CookieName){
        String CookieValue = null;

        CookieManager cookieManager = CookieManager.getInstance();
        String cookies = cookieManager.getCookie(siteName);
        if(cookies != null) {
            String[] temp = cookies.split(";");
            for (String ar1 : temp) {
                if (ar1.contains(CookieName)) {
                    String[] temp1 = ar1.split("=");
                    CookieValue = temp1[1];
                }
            }
        }
        return CookieValue;
    }


}

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



    <WebView
        android:id="@+id/activity_main_webview"
        android:layout_width="fill_parent"
        android:layout_height= "fill_parent"
        android:layout_weight="1.0" />

</RelativeLayout>

舱单在下面

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="selfservice.xxx.xxx.test"
    android:versionCode="2"
    android:versionName="1.1">

    <uses-sdk
        android:minSdkVersion="16"
        android:targetSdkVersion="17" />

    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.GET_ACCOUNTS" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
    <uses-permission android:name="android.permission.ACCESS_DOWNLOAD_MANAGER"/>

    <permission
        android:name="selfservice.xxx.xxx.test.permission.C2D_MESSAGE"
        android:protectionLevel="signature" />

    <uses-permission android:name="selfservice.xxx.xxx.test.gcm.permission.C2D_MESSAGE" />

    <application
        android:name="selfservice.xxx.xxx.test.PayrollApplication"
        android:allowBackup="true"
        android:icon="@mipmap/icon_pocket"
        android:label="Pocket HCM"
        android:theme="@style/AppTheme">
        <activity
            android:name="selfservice.xxx.xxx.test.MainActivity"
            android:label="Pocket HCM"
            android:screenOrientation="portrait" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="selfservice.xxx.xxx.test.SecondScreenActivity"
            android:screenOrientation="portrait"></activity>


        <receiver
            android:name="selfservice.xxx.xxx.test.GcmBroadcastReceiver"
            android:permission="com.google.android.c2dm.permission.SEND" >
            <intent-filter>

                <!-- Receives the actual messages. -->
                <action android:name="com.google.android.c2dm.intent.RECEIVE" />

                <category android:name="selfservice.xxx.xxx.test" />
            </intent-filter>
        </receiver>

        <service android:name="selfservice.xxx.xxx.test.GcmIntentService" />

        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />

        <activity
            android:name="selfservice.pockethcm.greytrix.test.ReceiveActivity">
        </activity>   

    </application>

</manifest>

安装应用程序后，它第一次工作，但当我们关闭并重新打开时，它崩溃了，不幸的是，应用程序已经关闭，你有任何想法，它将非常感谢：）

谢了！

Answer 1

以下是抛出NPE的罪魁祸首：

if (extras.getString("url").isEmpty()) {

您应该在此处检查URL是否为null:

url = extras.getString("url");
if(url == null){
Log.d("url status","its null");
}