Declare receiver in mainactivity

Question

I have a webView declared like this (MainActivity.java)

import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends AppCompatActivity
{
    public static WebView webView;
    WebView webView = (WebView) findViewById(R.id.webview);        
    webView.postUrl(url, postData.getBytes());
}

A receiver handles connection changes (BroadcastReceiver.java)

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;

public class ConnectionBroadReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

        ConnectivityManager cm = (ConnectivityManager)
                context.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo netInfo = cm.getActiveNetworkInfo();

        if (netInfo != null && netInfo.isConnectedOrConnecting()) {
            MainActivity.webView.reload();
        } else {
            MainActivity.webView.reload();
        }    
    }
}

The manifest (AndroidManifest.xml)

<application
        android:allowBackup="true"
        android:icon="@drawable/logo_full"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <receiver
            android:name=".ConnectionBroadReceiver">
            <intent-filter>
                <action android:name="android.net.conn.CONNECTIVITY_CHANGE"/>
            </intent-filter>
        </receiver>
    </application>

Because "webView" is a "public static WebView webView;" I can't invoke virtual method from another class..

onBroadReceiver: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.reload()' on a null object reference

How can I do ?

Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Reaz Murshed, Mar 06 '18 at 06:01
You don't have to make the `WebView` static. You can broadcast another message to your activity and handle the connection changes. http://inchoo.net/dev-talk/android-development/broadcast-receiver-from-activity/ — Sivakumar S, Mar 06 '18 at 06:03

Rajan Kali · Accepted Answer · 2018-03-06T07:06:00.983

Instead of registering receiver in manifest , register it in Activity and pass interface to interact on network state change

NetworkCallback.java

interface NetworkCallback{
  void onStateChange();
}

ConnectionBroadReceiver.java

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;

public class ConnectionBroadReceiver extends BroadcastReceiver {
   private NetworkCallback callback;

    public ConnectionBroadReceiver(NetworkCallback callback){
          this.callback = callback;
    }

    @Override
    public void onReceive(Context context, Intent intent) {

        ConnectivityManager cm = (ConnectivityManager)
                context.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo netInfo = cm.getActiveNetworkInfo();

        if (netInfo != null && netInfo.isConnectedOrConnecting()) {
            callback.onStateChange();
        } else {
             callback.onStateChange();
        }    
    }
}

Now in your Ativity

public class MainActivity extends AppCompatActivity
{
    private WebView webView;

   public void onCreate(Bundle savedInstanceState){
    // you code to set content view
    webView = (WebView) findViewById(R.id.webview);        
    webView.postUrl(url, postData.getBytes());
    registerReceiver(new ConnectionBroadReceiver(new NetworkCallback(){
          @Override
          public void onStateChange(){
               webview.reload();
          }
     }),new IntentFilter("android.net.conn.CONNECTIVITY_CHANGE")); 
  }
}

I have some syntax errors, could you check please ? Don't really see where I must add "android.net.conn.CONNECTIVITY_CHANGE" There is a ")" before a "}" in the answer so I don't see how to register the receiver.... — ysirob, Mar 06 '18 at 06:36
Thank you ^^ but "Local variable webView is accessed from within inner class; needs to be declared final" — ysirob, Mar 06 '18 at 06:57

Declare receiver in mainactivity

1 Answers1