*
* The {@link #onStart()} callback is always the first call you will receive and * is useful for doing one time setup or resource allocation before printing. You * will not receive a subsequent call here. *
** The {@link #onLayout(PrintAttributes, PrintAttributes, CancellationSignal, * LayoutResultCallback, Bundle)} callback requires that you layout the content * based on the current {@link PrintAttributes}. The execution of this method is * not considered completed until you invoke one of the methods on the passed in * callback instance. Hence, you will not receive a subsequent call to any other * method of this class until the execution of this method is complete by invoking * one of the callback methods. *
** The {@link #onWrite(PageRange[], ParcelFileDescriptor, CancellationSignal, * WriteResultCallback)} requires that you render and write the content of some * pages to the provided destination. The execution of this method is not * considered complete until you invoke one of the methods on the passed in * callback instance. Hence, you will not receive a subsequent call to any other * method of this class until the execution of this method is complete by invoking * one of the callback methods. You will never receive a sequence of one or more * calls to this method without a previous call to {@link #onLayout(PrintAttributes, * PrintAttributes, CancellationSignal, LayoutResultCallback, Bundle)}. *
** The {@link #onFinish()} callback is always the last call you will receive and * is useful for doing one time cleanup or resource deallocation after printing. * You will not receive a subsequent call here. *
* ** The APIs defined in this class are designed to enable doing part or all * of the work on an arbitrary thread. For example, if the printed content * does not depend on the UI state, i.e. on what is shown on the screen, then * you can offload the entire work on a dedicated thread, thus making your * application interactive while the print work is being performed. Note that * while your activity is covered by the system print UI and a user cannot * interact with it, doing the printing work on the main application thread * may affect the performance of your other application components as they * are also executed on that thread. *
** You can also do work on different threads, for example if you print UI * content, you can handle {@link #onStart()} and {@link #onLayout(PrintAttributes, * PrintAttributes, CancellationSignal, LayoutResultCallback, Bundle)} on * the UI thread (assuming onStart initializes resources needed for layout). * This will ensure that the UI does not change while you are laying out the * printed content. Then you can handle {@link #onWrite(PageRange[], ParcelFileDescriptor, * CancellationSignal, WriteResultCallback)} and {@link #onFinish()} on another * thread. This will ensure that the main thread is busy for a minimal amount of * time. Also this assumes that you will generate the printed content in * {@link #onLayout(PrintAttributes, PrintAttributes, CancellationSignal, * LayoutResultCallback, Bundle)} which is not mandatory. If you use multiple * threads, you are responsible for proper synchronization. *
*/ public abstract class PrintDocumentAdapter { /** * Extra: mapped to a boolean value that istrue if
* the current layout is for a print preview, false otherwise.
* This extra is provided in the {@link Bundle} argument of the {@link
* #onLayout(PrintAttributes, PrintAttributes, CancellationSignal,
* LayoutResultCallback, Bundle)} callback.
*
* @see #onLayout(PrintAttributes, PrintAttributes, CancellationSignal,
* LayoutResultCallback, Bundle)
*/
public static final String EXTRA_PRINT_PREVIEW = "EXTRA_PRINT_PREVIEW";
/**
* Called when printing starts. You can use this callback to allocate
* resources. This method is invoked on the main thread.
*/
public void onStart() {
/* do nothing - stub */
}
/**
* Called when the print attributes (page size, density, etc) changed
* giving you a chance to layout the content such that it matches the
* new constraints. This method is invoked on the main thread.
*
* After you are done laying out, you must invoke: {@link
* LayoutResultCallback#onLayoutFinished(PrintDocumentInfo, boolean)} with
* the last argument true or false depending on
* whether the layout changed the content or not, respectively; or {@link
* LayoutResultCallback#onLayoutFailed(CharSequence)}, if an error occurred;
* or {@link LayoutResultCallback#onLayoutCancelled()} if layout was
* cancelled in a response to a cancellation request via the passed in
* {@link CancellationSignal}. Note that you must call one of
* the methods of the given callback for this method to be considered complete
* which is you will not receive any calls to this adapter until the current
* layout operation is complete by invoking a method on the callback instance.
* The callback methods can be invoked from an arbitrary thread.
*
* One of the arguments passed to this method is a {@link CancellationSignal} * which is used to propagate requests from the system to your application for * canceling the current layout operation. For example, a cancellation may be * requested if the user changes a print option that may affect layout while * you are performing a layout operation. In such a case the system will make * an attempt to cancel the current layout as another one will have to be performed. * Typically, you should register a cancellation callback in the cancellation * signal. The cancellation callback will not be made on the * main thread and can be registered as follows: *
*
* cancellationSignal.setOnCancelListener(new OnCancelListener() {
* @Override
* public void onCancel() {
* // Cancel layout
* }
* });
*
* * Note: If the content is large and a layout will be * performed, it is a good practice to schedule the work on a dedicated * thread and register an observer in the provided {@link * CancellationSignal} upon invocation of which you should stop the * layout. *
* * @param oldAttributes The old print attributes. * @param newAttributes The new print attributes. * @param cancellationSignal Signal for observing cancel layout requests. * @param callback Callback to inform the system for the layout result. * @param extras Additional information about how to layout the content. * * @see LayoutResultCallback * @see CancellationSignal * @see #EXTRA_PRINT_PREVIEW */ public abstract void onLayout(PrintAttributes oldAttributes, PrintAttributes newAttributes, CancellationSignal cancellationSignal, LayoutResultCallback callback, Bundle extras); /** * Called when specific pages of the content should be written in the * form of a PDF file to the given file descriptor. This method is invoked * on the main thread. ** After you are done writing, you should close the file descriptor and * invoke {@link WriteResultCallback#onWriteFinished(PageRange[])}, if writing * completed successfully; or {@link WriteResultCallback#onWriteFailed( * CharSequence)}, if an error occurred; or {@link WriteResultCallback#onWriteCancelled()}, * if writing was cancelled in a response to a cancellation request via the passed * in {@link CancellationSignal}. Note that you must call one of * the methods of the given callback for this method to be considered complete which * is you will not receive any calls to this adapter until the current write * operation is complete by invoking a method on the callback instance. The callback * methods can be invoked from an arbitrary thread. *
** One of the arguments passed to this method is a {@link CancellationSignal} * which is used to propagate requests from the system to your application for * canceling the current write operation. For example, a cancellation may be * requested if the user changes a print option that may affect layout while * you are performing a write operation. In such a case the system will make * an attempt to cancel the current write as a layout will have to be performed * which then may be followed by a write. Typically, you should register a * cancellation callback in the cancellation signal. The cancellation callback * will not be made on the main thread and can be registered * as follows: *
*
* cancellationSignal.setOnCancelListener(new OnCancelListener() {
* @Override
* public void onCancel() {
* // Cancel write
* }
* });
*
* * Note: If the printed content is large, it is a good * practice to schedule writing it on a dedicated thread and register an * observer in the provided {@link CancellationSignal} upon invocation of * which you should stop writing. *
* * @param pages The pages whose content to print - non-overlapping in ascending order. * @param destination The destination file descriptor to which to write. * @param cancellationSignal Signal for observing cancel writing requests. * @param callback Callback to inform the system for the write result. * * @see WriteResultCallback * @see CancellationSignal */ public abstract void onWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal, WriteResultCallback callback); /** * Called when printing finishes. You can use this callback to release * resources acquired in {@link #onStart()}. This method is invoked on * the main thread. */ public void onFinish() { /* do nothing - stub */ } /** * Base class for implementing a callback for the result of {@link * PrintDocumentAdapter#onWrite(PageRange[], ParcelFileDescriptor, CancellationSignal, * WriteResultCallback)}. */ public static abstract class WriteResultCallback { /** * @hide */ public WriteResultCallback() { /* do nothing - hide constructor */ } /** * Notifies that all the data was written. * * @param pages The pages that were written. Cannot benull
* or empty.
*/
public void onWriteFinished(PageRange[] pages) {
/* do nothing - stub */
}
/**
* Notifies that an error occurred while writing the data.
*
* @param error The localized error message.
* shown to the user. May be null if error is unknown.
*/
public void onWriteFailed(CharSequence error) {
/* do nothing - stub */
}
/**
* Notifies that write was cancelled as a result of a cancellation request.
*/
public void onWriteCancelled() {
/* do nothing - stub */
}
}
/**
* Base class for implementing a callback for the result of {@link
* PrintDocumentAdapter#onLayout(PrintAttributes, PrintAttributes,
* CancellationSignal, LayoutResultCallback, Bundle)}.
*/
public static abstract class LayoutResultCallback {
/**
* @hide
*/
public LayoutResultCallback() {
/* do nothing - hide constructor */
}
/**
* Notifies that the layout finished and whether the content changed.
*
* @param info An info object describing the document. Cannot be null.
* @param changed Whether the layout changed.
*
* @see PrintDocumentInfo
*/
public void onLayoutFinished(PrintDocumentInfo info, boolean changed) {
/* do nothing - stub */
}
/**
* Notifies that an error occurred while laying out the document.
*
* @param error The localized error message.
* shown to the user. May be null if error is unknown.
*/
public void onLayoutFailed(CharSequence error) {
/* do nothing - stub */
}
/**
* Notifies that layout was cancelled as a result of a cancellation request.
*/
public void onLayoutCancelled() {
/* do nothing - stub */
}
}
}