ReceiverRegistrar.java

package com.github.curioustechizen.safereg;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.v4.util.ArrayMap;

/**
 * Helper class to keep track of what {@code BroadcastReceiver}s have been
 * registered for this context. Requests for registering a new receiver will act
 * only if the not already registered. Similarly, requests for unregistering a
 * receiver will act only if the register is already registered.
 * 
 * @author Kiran Rao
 * 
 */
public class ReceiverRegistrar {

	private Context mContext;
	private ArrayMap<BroadcastReceiver, Intent> mReceiverMap;

	/**
	 * Construct a new instance of the registrar.
	 * 
	 * @param context
	 *            The context that is used for registering the receiver
	 */
	public ReceiverRegistrar(Context context) {
		mContext = context;
		mReceiverMap = new ArrayMap<BroadcastReceiver, Intent>();
	}

	/**
	 * Register a {@code BroadcastReceiver}. If the receiver is already
	 * registered then this method will simply return the {@code Intent}
	 * returned by the previous {@code registerReceiver} call.
	 * 
	 * @see {@link Context#registerReceiver(BroadcastReceiver, IntentFilter)}
	 * @param receiver
	 *            The BroadcastReceiver to handle the broadcast
	 * @param filter
	 *            The filter to select the broadcasts to be handled
	 * @return The first sticky intent found that matches filter, or null if
	 *         there are none. If this receiver has already been registered,
	 *         then the return value is the intent that was returned when the
	 *         receiver was originally registered.
	 */
	public Intent safeRegisterReceiver(BroadcastReceiver receiver,
			IntentFilter filter) {
		if (!mReceiverMap.containsKey(receiver)) {
			Intent intent = mContext.registerReceiver(receiver, filter);
			mReceiverMap.put(receiver, intent);
			return intent;
		} else {
			return mReceiverMap.get(receiver);
		}
	}

	/**
	 * Unregister a {@code BroadcastReceiver}, if it hasn't been registered
	 * already.
	 * 
	 * @param receiver
	 */
	public void safeUnregisterReceiver(BroadcastReceiver receiver) {
		if (mReceiverMap.containsKey(receiver)) {
			mContext.unregisterReceiver(receiver);
			mReceiverMap.remove(receiver);
		}
	}

	/**
	 * Unregister all {@code BroadcastReceiver}s registered with this context.
	 */
	public void safeUnregisterAllReceivers() {
		for (BroadcastReceiver receiver : mReceiverMap.keySet()) {
			safeUnregisterReceiver(receiver);
		}
	}
}

SampleNaiveActivity.java

package com.github.curioustechizen.safereg;

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.IntentFilter;
import android.os.Bundle;

/*
 * Naive implementation of registering and un-registering multiple BroadcastReceivers 
 * in an Activity using boolean flags to keep track of whether they have been registered.
 * 
 * You probably want to use ReceiverRegistrar instead of this as demonstrated in SampleRecommendedActivity.java 
 */
public class SampleNaiveActivity extends Activity {

	private BroadcastReceiver mConnectivityReceiver, mBatteryReceiver;
	private IntentFilter mConnectivityFilter, mBatteryFilter;
	private boolean mRegisteredConnectivityReceiver,
			mRegisteredBatteryReceiver;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		/*
		 * Initialize the BroadcastReceivers here Setup the IntentFilters here
		 */

	}

	@Override
	protected void onResume() {
		super.onResume();
		/*
		 * Register your receivers in onResume
		 */
		registerBatteryReceiver();
		registerConnectivityReceiver();

	}

	private void onBatteryLow() {
		/*
		 * Maybe when the battery goes low you want to unregister a few
		 * receivers?
		 */
		unregisterConnectivityReceiver();
	}

	@Override
	protected void onPause() {
		super.onPause();
		/*
		 * In onPause, unregister all remaining registered receivers
		 */
		unregisterBatteryReceiver();
		unregisterConnectivityReceiver();
	}

	private void registerBatteryReceiver() {
		if (!mRegisteredBatteryReceiver) {
			mRegisteredBatteryReceiver = true;
			registerReceiver(mBatteryReceiver, mBatteryFilter);
		}
	}

	private void unregisterBatteryReceiver() {
		if (mRegisteredBatteryReceiver) {
			mRegisteredBatteryReceiver = false;
			unregisterReceiver(mBatteryReceiver);
		}
	}

	private void registerConnectivityReceiver() {
		if (!mRegisteredConnectivityReceiver) {
			mRegisteredConnectivityReceiver = true;
			registerReceiver(mConnectivityReceiver, mConnectivityFilter);
		}
	}

	private void unregisterConnectivityReceiver() {
		if (mRegisteredConnectivityReceiver) {
			mRegisteredConnectivityReceiver = false;
			unregisterReceiver(mConnectivityReceiver);
		}
	}
}

SampleRecommendedActivity.java

package com.github.curioustechizen.safereg;

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.IntentFilter;
import android.os.Bundle;

public class SampleRecommendedActivity extends Activity {

	private BroadcastReceiver mConnectivityReceiver, mBatteryReceiver;
	private IntentFilter mConnectivityFilter, mBatteryFilter;
	private ReceiverRegistrar mReceiverRegistrar;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		/*
		 * Initialize the BroadcastReceivers here and Setup the IntentFilters here
		 */
		mReceiverRegistrar = new ReceiverRegistrar(this);
	}

	@Override
	protected void onResume() {
		super.onResume();
		/*
		 * Register your receivers in onResume
		 */
		mReceiverRegistrar.safeRegisterReceiver(mBatteryReceiver,
				mBatteryFilter);
		mReceiverRegistrar.safeRegisterReceiver(mConnectivityReceiver,
				mConnectivityFilter);
	}

	private void onBatteryLow() {
		/*
		 * Maybe when the battery goes low you want to unregister a few
		 * receivers?
		 */
		mReceiverRegistrar.safeUnregisterReceiver(mConnectivityReceiver);
	}

	@Override
	protected void onPause() {
		super.onPause();
		/*
		 * In onPause, unregister all remaining registered receivers
		 */
		mReceiverRegistrar.safeUnregisterAllReceivers();
	}
}