/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.printservice;

import android.annotation.NonNull;
import android.content.pm.ParceledListSlice;
import android.os.CancellationSignal;
import android.os.RemoteException;
import android.print.PrinterCapabilitiesInfo;
import android.print.PrinterId;
import android.print.PrinterInfo;
import android.util.ArrayMap;
import android.util.Log;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

This class encapsulates the interaction between a print service and the system during printer discovery. During printer discovery you are responsible for adding discovered printers, removing previously added printers that disappeared, and updating already added printers.

During the lifetime of this session you may be asked to start and stop performing printer discovery multiple times. You will receive a call to onStartPrinterDiscovery(List<PrinterId>) to start printer discovery and a call to onStopPrinterDiscovery() to stop printer discovery. When the system is no longer interested in printers discovered by this session you will receive a call to onDestroy() at which point the system will no longer call into the session and all the session methods will do nothing.

Discovered printers are added by invoking addPrinters(List<PrinterInfo>). Added printers that disappeared are removed by invoking removePrinters(List<PrinterId>). Added printers whose properties or capabilities changed are updated through a call to addPrinters(List<PrinterInfo>). The printers added in this session can be acquired via getPrinters() where the returned printers will be an up-to-date snapshot of the printers that you reported during the session. Printers are not persisted across sessions.

The system will make a call to onValidatePrinters(List<PrinterId>) if you need to update some printers. It is possible that you add a printer without specifying its capabilities. This enables you to avoid querying all discovered printers for their capabilities, rather querying the capabilities of a printer only if necessary. For example, the system will request that you update a printer if it gets selected by the user. When validating printers you do not need to provide the printers' capabilities but may do so.

If the system is interested in being constantly updated for the state of a printer you will receive a call to onStartPrinterStateTracking(PrinterId) after which you will have to do a best effort to keep the system updated for changes in the printer state and capabilities. You also must update the printer capabilities if you did not provide them when adding it, or the printer will be ignored. When the system is no longer interested in getting updates for a printer you will receive a call to onStopPrinterStateTracking(PrinterId).

Note: All callbacks in this class are executed on the main application thread. You also have to invoke any method of this class on the main application thread.

/** * This class encapsulates the interaction between a print service and the * system during printer discovery. During printer discovery you are responsible * for adding discovered printers, removing previously added printers that * disappeared, and updating already added printers. * <p> * During the lifetime of this session you may be asked to start and stop * performing printer discovery multiple times. You will receive a call to {@link * PrinterDiscoverySession#onStartPrinterDiscovery(List)} to start printer * discovery and a call to {@link PrinterDiscoverySession#onStopPrinterDiscovery()} * to stop printer discovery. When the system is no longer interested in printers * discovered by this session you will receive a call to {@link #onDestroy()} at * which point the system will no longer call into the session and all the session * methods will do nothing. * </p> * <p> * Discovered printers are added by invoking {@link * PrinterDiscoverySession#addPrinters(List)}. Added printers that disappeared are * removed by invoking {@link PrinterDiscoverySession#removePrinters(List)}. Added * printers whose properties or capabilities changed are updated through a call to * {@link PrinterDiscoverySession#addPrinters(List)}. The printers added in this * session can be acquired via {@link #getPrinters()} where the returned printers * will be an up-to-date snapshot of the printers that you reported during the * session. Printers are <strong>not</strong> persisted across sessions. * </p> * <p> * The system will make a call to {@link #onValidatePrinters(List)} if you * need to update some printers. It is possible that you add a printer without * specifying its capabilities. This enables you to avoid querying all discovered * printers for their capabilities, rather querying the capabilities of a printer * only if necessary. For example, the system will request that you update a printer * if it gets selected by the user. When validating printers you do not need to * provide the printers' capabilities but may do so. * </p> * <p> * If the system is interested in being constantly updated for the state of a * printer you will receive a call to {@link #onStartPrinterStateTracking(PrinterId)} * after which you will have to do a best effort to keep the system updated for * changes in the printer state and capabilities. You also <strong>must</strong> * update the printer capabilities if you did not provide them when adding it, or * the printer will be ignored. When the system is no longer interested in getting * updates for a printer you will receive a call to {@link #onStopPrinterStateTracking( * PrinterId)}. * </p> * <p> * <strong>Note: </strong> All callbacks in this class are executed on the main * application thread. You also have to invoke any method of this class on the main * application thread. * </p> */
public abstract class PrinterDiscoverySession { private static final String LOG_TAG = "PrinterDiscoverySession"; private static int sIdCounter = 0; private final int mId; private final ArrayMap<PrinterId, PrinterInfo> mPrinters = new ArrayMap<PrinterId, PrinterInfo>(); private final List<PrinterId> mTrackedPrinters = new ArrayList<PrinterId>(); private ArrayMap<PrinterId, PrinterInfo> mLastSentPrinters; private IPrintServiceClient mObserver; private boolean mIsDestroyed; private boolean mIsDiscoveryStarted;
Constructor.
/** * Constructor. */
public PrinterDiscoverySession() { mId = sIdCounter++; } void setObserver(IPrintServiceClient observer) { mObserver = observer; // If some printers were added in the method that // created the session, send them over. if (!mPrinters.isEmpty()) { try { mObserver.onPrintersAdded(new ParceledListSlice<PrinterInfo>(getPrinters())); } catch (RemoteException re) { Log.e(LOG_TAG, "Error sending added printers", re); } } } int getId() { return mId; }
Gets the printers reported in this session. For example, if you add two printers and remove one of them, the returned list will contain only the printer that was added but not removed.

Note: Calls to this method after the session is destroyed, that is after the onDestroy() callback, will be ignored.

See Also:
Returns:The printers.
/** * Gets the printers reported in this session. For example, if you add two * printers and remove one of them, the returned list will contain only * the printer that was added but not removed. * <p> * <strong>Note: </strong> Calls to this method after the session is * destroyed, that is after the {@link #onDestroy()} callback, will be ignored. * </p> * * @return The printers. * * @see #addPrinters(List) * @see #removePrinters(List) * @see #isDestroyed() */
public final @NonNull List<PrinterInfo> getPrinters() { PrintService.throwIfNotCalledOnMainThread(); if (mIsDestroyed) { return Collections.emptyList(); } return new ArrayList<PrinterInfo>(mPrinters.values()); }
Adds discovered printers. Adding an already added printer updates it. Removed printers can be added again. You can call this method multiple times during the life of this session. Duplicates will be ignored.

Note: Calls to this method after the session is destroyed, that is after the onDestroy() callback, will be ignored.

Params:
  • printers – The printers to add.
See Also:
/** * Adds discovered printers. Adding an already added printer updates it. * Removed printers can be added again. You can call this method multiple * times during the life of this session. Duplicates will be ignored. * <p> * <strong>Note: </strong> Calls to this method after the session is * destroyed, that is after the {@link #onDestroy()} callback, will be ignored. * </p> * * @param printers The printers to add. * * @see #removePrinters(List) * @see #getPrinters() * @see #isDestroyed() */
public final void addPrinters(@NonNull List<PrinterInfo> printers) { PrintService.throwIfNotCalledOnMainThread(); // If the session is destroyed - nothing do to. if (mIsDestroyed) { Log.w(LOG_TAG, "Not adding printers - session destroyed."); return; } if (mIsDiscoveryStarted) { // If during discovery, add the new printers and send them. List<PrinterInfo> addedPrinters = null; final int addedPrinterCount = printers.size(); for (int i = 0; i < addedPrinterCount; i++) { PrinterInfo addedPrinter = printers.get(i); PrinterInfo oldPrinter = mPrinters.put(addedPrinter.getId(), addedPrinter); if (oldPrinter == null || !oldPrinter.equals(addedPrinter)) { if (addedPrinters == null) { addedPrinters = new ArrayList<PrinterInfo>(); } addedPrinters.add(addedPrinter); } } // Send the added printers, if such. if (addedPrinters != null) { try { mObserver.onPrintersAdded(new ParceledListSlice<PrinterInfo>(addedPrinters)); } catch (RemoteException re) { Log.e(LOG_TAG, "Error sending added printers", re); } } } else { // Remember the last sent printers if needed. if (mLastSentPrinters == null) { mLastSentPrinters = new ArrayMap<PrinterId, PrinterInfo>(mPrinters); } // Update the printers. final int addedPrinterCount = printers.size(); for (int i = 0; i < addedPrinterCount; i++) { PrinterInfo addedPrinter = printers.get(i); if (mPrinters.get(addedPrinter.getId()) == null) { mPrinters.put(addedPrinter.getId(), addedPrinter); } } } }
Removes added printers. Removing an already removed or never added printer has no effect. Removed printers can be added again. You can call this method multiple times during the lifetime of this session.

Note: Calls to this method after the session is destroyed, that is after the onDestroy() callback, will be ignored.

Params:
  • printerIds – The ids of the removed printers.
See Also:
/** * Removes added printers. Removing an already removed or never added * printer has no effect. Removed printers can be added again. You can * call this method multiple times during the lifetime of this session. * <p> * <strong>Note: </strong> Calls to this method after the session is * destroyed, that is after the {@link #onDestroy()} callback, will be ignored. * </p> * * @param printerIds The ids of the removed printers. * * @see #addPrinters(List) * @see #getPrinters() * @see #isDestroyed() */
public final void removePrinters(@NonNull List<PrinterId> printerIds) { PrintService.throwIfNotCalledOnMainThread(); // If the session is destroyed - nothing do to. if (mIsDestroyed) { Log.w(LOG_TAG, "Not removing printers - session destroyed."); return; } if (mIsDiscoveryStarted) { // If during discovery, remove existing printers and send them. List<PrinterId> removedPrinterIds = new ArrayList<PrinterId>(); final int removedPrinterIdCount = printerIds.size(); for (int i = 0; i < removedPrinterIdCount; i++) { PrinterId removedPrinterId = printerIds.get(i); if (mPrinters.remove(removedPrinterId) != null) { removedPrinterIds.add(removedPrinterId); } } // Send the removed printers, if such. if (!removedPrinterIds.isEmpty()) { try { mObserver.onPrintersRemoved(new ParceledListSlice<PrinterId>( removedPrinterIds)); } catch (RemoteException re) { Log.e(LOG_TAG, "Error sending removed printers", re); } } } else { // Remember the last sent printers if needed. if (mLastSentPrinters == null) { mLastSentPrinters = new ArrayMap<PrinterId, PrinterInfo>(mPrinters); } // Update the printers. final int removedPrinterIdCount = printerIds.size(); for (int i = 0; i < removedPrinterIdCount; i++) { PrinterId removedPrinterId = printerIds.get(i); mPrinters.remove(removedPrinterId); } } } private void sendOutOfDiscoveryPeriodPrinterChanges() { // Noting changed since the last discovery period - nothing to do. if (mLastSentPrinters == null || mLastSentPrinters.isEmpty()) { mLastSentPrinters = null; return; } // Determine the added printers. List<PrinterInfo> addedPrinters = null; for (PrinterInfo printer : mPrinters.values()) { PrinterInfo sentPrinter = mLastSentPrinters.get(printer.getId()); if (sentPrinter == null || !sentPrinter.equals(printer)) { if (addedPrinters == null) { addedPrinters = new ArrayList<PrinterInfo>(); } addedPrinters.add(printer); } } // Send the added printers, if such. if (addedPrinters != null) { try { mObserver.onPrintersAdded(new ParceledListSlice<PrinterInfo>(addedPrinters)); } catch (RemoteException re) { Log.e(LOG_TAG, "Error sending added printers", re); } } // Determine the removed printers. List<PrinterId> removedPrinterIds = null; for (PrinterInfo sentPrinter : mLastSentPrinters.values()) { if (!mPrinters.containsKey(sentPrinter.getId())) { if (removedPrinterIds == null) { removedPrinterIds = new ArrayList<PrinterId>(); } removedPrinterIds.add(sentPrinter.getId()); } } // Send the removed printers, if such. if (removedPrinterIds != null) { try { mObserver.onPrintersRemoved(new ParceledListSlice<PrinterId>(removedPrinterIds)); } catch (RemoteException re) { Log.e(LOG_TAG, "Error sending removed printers", re); } } mLastSentPrinters = null; }
Callback asking you to start printer discovery. Discovered printers should be added via calling addPrinters(List<PrinterInfo>). Added printers that disappeared should be removed via calling removePrinters(List<PrinterId>). Added printers whose properties or capabilities changed should be updated via calling addPrinters(List<PrinterInfo>). You will receive a call to onStopPrinterDiscovery() when you should stop printer discovery.

During the lifetime of this session all printers that are known to your print service have to be added. The system does not retain any printers across sessions. However, if you were asked to start and then stop performing printer discovery in this session, then a subsequent discovering should not re-discover already discovered printers. You can get the printers reported during this session by calling getPrinters().

Note: You are also given a list of printers whose availability has to be checked first. For example, these printers could be the user's favorite ones, therefore they have to be verified first. You do not need to provide the capabilities of the printers, rather verify whether they exist similarly to onValidatePrinters(List<PrinterId>).

Params:
  • priorityList – The list of printers to validate first. Never null.
See Also:
/** * Callback asking you to start printer discovery. Discovered printers should be * added via calling {@link #addPrinters(List)}. Added printers that disappeared * should be removed via calling {@link #removePrinters(List)}. Added printers * whose properties or capabilities changed should be updated via calling {@link * #addPrinters(List)}. You will receive a call to {@link #onStopPrinterDiscovery()} * when you should stop printer discovery. * <p> * During the lifetime of this session all printers that are known to your print * service have to be added. The system does not retain any printers across sessions. * However, if you were asked to start and then stop performing printer discovery * in this session, then a subsequent discovering should not re-discover already * discovered printers. You can get the printers reported during this session by * calling {@link #getPrinters()}. * </p> * <p> * <strong>Note: </strong>You are also given a list of printers whose availability * has to be checked first. For example, these printers could be the user's favorite * ones, therefore they have to be verified first. You do <strong>not need</strong> * to provide the capabilities of the printers, rather verify whether they exist * similarly to {@link #onValidatePrinters(List)}. * </p> * * @param priorityList The list of printers to validate first. Never null. * * @see #onStopPrinterDiscovery() * @see #addPrinters(List) * @see #removePrinters(List) * @see #isPrinterDiscoveryStarted() */
public abstract void onStartPrinterDiscovery(@NonNull List<PrinterId> priorityList);
Callback notifying you that you should stop printer discovery.
See Also:
/** * Callback notifying you that you should stop printer discovery. * * @see #onStartPrinterDiscovery(List) * @see #isPrinterDiscoveryStarted() */
public abstract void onStopPrinterDiscovery();
Callback asking you to validate that the given printers are valid, that is they exist. You are responsible for checking whether these printers exist and for the ones that do exist notify the system via calling addPrinters(List<PrinterInfo>).

Note: You are not required to provide the printer capabilities when updating the printers that do exist.

Params:
  • printerIds – The printers to validate.
See Also:
/** * Callback asking you to validate that the given printers are valid, that * is they exist. You are responsible for checking whether these printers * exist and for the ones that do exist notify the system via calling * {@link #addPrinters(List)}. * <p> * <strong>Note: </strong> You are <strong>not required</strong> to provide * the printer capabilities when updating the printers that do exist. * <p> * * @param printerIds The printers to validate. * * @see android.print.PrinterInfo.Builder#setCapabilities(PrinterCapabilitiesInfo) * PrinterInfo.Builder.setCapabilities(PrinterCapabilitiesInfo) */
public abstract void onValidatePrinters(@NonNull List<PrinterId> printerIds);
Callback asking you to start tracking the state of a printer. Tracking the state means that you should do a best effort to observe the state of this printer and notify the system if that state changes via calling addPrinters(List<PrinterInfo>).

Note: A printer can be initially added without its capabilities to avoid polling printers that the user will not select. However, after this method is called you are expected to update the printer including its capabilities. Otherwise, the printer will be ignored.

A scenario when you may be requested to track a printer's state is if the user selects that printer and the system has to present print options UI based on the printer's capabilities. In this case the user should be promptly informed if, for example, the printer becomes unavailable.

Params:
  • printerId – The printer to start tracking.
See Also:
/** * Callback asking you to start tracking the state of a printer. Tracking * the state means that you should do a best effort to observe the state * of this printer and notify the system if that state changes via calling * {@link #addPrinters(List)}. * <p> * <strong>Note: </strong> A printer can be initially added without its * capabilities to avoid polling printers that the user will not select. * However, after this method is called you are expected to update the * printer <strong>including</strong> its capabilities. Otherwise, the * printer will be ignored. * <p> * <p> * A scenario when you may be requested to track a printer's state is if * the user selects that printer and the system has to present print * options UI based on the printer's capabilities. In this case the user * should be promptly informed if, for example, the printer becomes * unavailable. * </p> * * @param printerId The printer to start tracking. * * @see #onStopPrinterStateTracking(PrinterId) * @see android.print.PrinterInfo.Builder#setCapabilities(PrinterCapabilitiesInfo) * PrinterInfo.Builder.setCapabilities(PrinterCapabilitiesInfo) */
public abstract void onStartPrinterStateTracking(@NonNull PrinterId printerId);
Called by the system to request the custom icon for a printer. Once the icon is available the print services uses CustomPrinterIconCallback.onCustomPrinterIconLoaded to send the icon to the system.
Params:
  • printerId – The printer to icon belongs to.
  • cancellationSignal – Signal used to cancel the request.
  • callback – Callback for returning the icon to the system.
See Also:
/** * Called by the system to request the custom icon for a printer. Once the icon is available the * print services uses {@link CustomPrinterIconCallback#onCustomPrinterIconLoaded} to send the * icon to the system. * * @param printerId The printer to icon belongs to. * @param cancellationSignal Signal used to cancel the request. * @param callback Callback for returning the icon to the system. * * @see android.print.PrinterInfo.Builder#setHasCustomPrinterIcon(boolean) */
public void onRequestCustomPrinterIcon(@NonNull PrinterId printerId, @NonNull CancellationSignal cancellationSignal, @NonNull CustomPrinterIconCallback callback) { }
Callback asking you to stop tracking the state of a printer. The passed in printer id is the one for which you received a call to onStartPrinterStateTracking(PrinterId).
Params:
  • printerId – The printer to stop tracking.
See Also:
/** * Callback asking you to stop tracking the state of a printer. The passed * in printer id is the one for which you received a call to {@link * #onStartPrinterStateTracking(PrinterId)}. * * @param printerId The printer to stop tracking. * * @see #onStartPrinterStateTracking(PrinterId) */
public abstract void onStopPrinterStateTracking(@NonNull PrinterId printerId);
Gets the printers that should be tracked. These are printers that are important to the user and for which you received a call to onStartPrinterStateTracking(PrinterId) asking you to observer their state and reporting it to the system via addPrinters(List<PrinterInfo>). You will receive a call to onStopPrinterStateTracking(PrinterId) if you should stop tracking a printer.

Note: Calls to this method after the session is destroyed, that is after the onDestroy() callback, will be ignored.

See Also:
Returns:The printers.
/** * Gets the printers that should be tracked. These are printers that are * important to the user and for which you received a call to {@link * #onStartPrinterStateTracking(PrinterId)} asking you to observer their * state and reporting it to the system via {@link #addPrinters(List)}. * You will receive a call to {@link #onStopPrinterStateTracking(PrinterId)} * if you should stop tracking a printer. * <p> * <strong>Note: </strong> Calls to this method after the session is * destroyed, that is after the {@link #onDestroy()} callback, will be ignored. * </p> * * @return The printers. * * @see #onStartPrinterStateTracking(PrinterId) * @see #onStopPrinterStateTracking(PrinterId) * @see #isDestroyed() */
public final @NonNull List<PrinterId> getTrackedPrinters() { PrintService.throwIfNotCalledOnMainThread(); if (mIsDestroyed) { return Collections.emptyList(); } return new ArrayList<PrinterId>(mTrackedPrinters); }
Notifies you that the session is destroyed. After this callback is invoked any calls to the methods of this class will be ignored, isDestroyed() will return true and you will also no longer receive callbacks.
See Also:
/** * Notifies you that the session is destroyed. After this callback is invoked * any calls to the methods of this class will be ignored, {@link #isDestroyed()} * will return true and you will also no longer receive callbacks. * * @see #isDestroyed() */
public abstract void onDestroy();
Gets whether the session is destroyed.
See Also:
Returns:Whether the session is destroyed.
/** * Gets whether the session is destroyed. * * @return Whether the session is destroyed. * * @see #onDestroy() */
public final boolean isDestroyed() { PrintService.throwIfNotCalledOnMainThread(); return mIsDestroyed; }
Gets whether printer discovery is started.
See Also:
Returns:Whether printer discovery is destroyed.
/** * Gets whether printer discovery is started. * * @return Whether printer discovery is destroyed. * * @see #onStartPrinterDiscovery(List) * @see #onStopPrinterDiscovery() */
public final boolean isPrinterDiscoveryStarted() { PrintService.throwIfNotCalledOnMainThread(); return mIsDiscoveryStarted; } void startPrinterDiscovery(@NonNull List<PrinterId> priorityList) { if (!mIsDestroyed) { mIsDiscoveryStarted = true; sendOutOfDiscoveryPeriodPrinterChanges(); if (priorityList == null) { priorityList = Collections.emptyList(); } onStartPrinterDiscovery(priorityList); } } void stopPrinterDiscovery() { if (!mIsDestroyed) { mIsDiscoveryStarted = false; onStopPrinterDiscovery(); } } void validatePrinters(@NonNull List<PrinterId> printerIds) { if (!mIsDestroyed && mObserver != null) { onValidatePrinters(printerIds); } } void startPrinterStateTracking(@NonNull PrinterId printerId) { if (!mIsDestroyed && mObserver != null && !mTrackedPrinters.contains(printerId)) { mTrackedPrinters.add(printerId); onStartPrinterStateTracking(printerId); } }
Request the custom icon for a printer.
Params:
  • printerId – The printer to icon belongs to.
See Also:
/** * Request the custom icon for a printer. * * @param printerId The printer to icon belongs to. * @see android.print.PrinterInfo.Builder#setHasCustomPrinterIcon() */
void requestCustomPrinterIcon(@NonNull PrinterId printerId) { if (!mIsDestroyed && mObserver != null) { CustomPrinterIconCallback callback = new CustomPrinterIconCallback(printerId, mObserver); onRequestCustomPrinterIcon(printerId, new CancellationSignal(), callback); } } void stopPrinterStateTracking(@NonNull PrinterId printerId) { if (!mIsDestroyed && mObserver != null && mTrackedPrinters.remove(printerId)) { onStopPrinterStateTracking(printerId); } } void destroy() { if (!mIsDestroyed) { mIsDestroyed = true; mIsDiscoveryStarted = false; mPrinters.clear(); mLastSentPrinters = null; mObserver = null; onDestroy(); } } }