The technical principles of the Android support library printing framework 6: Customized printing function expansion Cure

The technical principle of the Android support library printing framework 6: Custom printing function expansion In the Android support library, the printing framework provides a convenient printing function, allowing users to easily print documents, photos and other content in the application.However, sometimes we may need to customize the printing function to meet specific business needs.This article will introduce how to customize the printing needs by expanding the printing function. 1. Create a custom printing function To achieve custom printing function, first of all, a class of printing function is needed.This class should inherit the PrintdocumentAdapter class and implement its abstract method.For example, we can create a CustomPrintadapter class to achieve custom printing function. public class CustomPrintAdapter extends PrintDocumentAdapter { ... @Override public void onStart() { // Print the operation at the beginning } @Override public void onLayout(PrintAttributes oldAttributes, PrintAttributes newAttributes, CancellationSignal cancellationSignal, LayoutResultCallback callback, Bundle extras) { // Operation when printing layout } @Override public void onWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal, WriteResultCallback callback) { // The operation when writing the printing content } @Override public void onFinish() { // The operation when the print is completed } ... } 2. Use custom printing function in print preview Next, use our custom printing function in the print preview interface.We can obtain the print manager through the PrintManager class and call its print method to achieve printing preview.In the Print method, we can pass into the CustomPrintadapter instance created above and specify the printed document name. PrintManager printManager = (PrintManager) getSystemService(Context.PRINT_SERVICE); String jobName = getString(R.string.print_job_name); printManager.print(jobName, new CustomPrintAdapter(), null); 3. Implement custom print content In custom printing functions, we can achieve different print content according to specific needs.For example, we can get the content to be printed in the Onwrite method and write it to the printed destination.Below is a simple example to demonstrate how to write the text content into the printed destination. @Override public void onWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal, WriteResultCallback callback) { FileOutputStream output = new FileOutputStream(destination.getFileDescriptor()); PrintWriter writer = new PrintWriter(output); writer.println("This is a sample print output"); writer.flush(); writer.close(); callback.onWriteFinished(new PageRange[]{PageRange.ALL_PAGES}); } 4. Capture printing errors In custom printing functions, we can also capture and process errors that may occur during the printing process.You can cancel the printing operation through the parameter of the onLayout and onwrite methods of the Printdocumentadapter class, and process the error by passing related error messages by passing related error messages. @Override public void onWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal, WriteResultCallback callback) { if (cancellationSignal.isCanceled()) { callback.onWriteCancelled(); return; } try { // Perform print operations } catch (Exception e) { callback.onWriteFailed(e.getMessage()); } callback.onWriteFinished(new PageRange[]{PageRange.ALL_PAGES}); } Through the above steps, we can realize the custom printing function, and customize the printing content and processing errors according to business needs.In this way, we can more flexibly meet the printing needs in different scenarios. Summarize This article introduces how to achieve custom printing needs by expanding the printing function.We first create a custom printing class inherited from the Printdocumentadapter class, and then use the custom printing function in the print preview interface, and achieve custom print content and error processing according to specific needs.Through these steps, we can flexibly implement more customized printing functions.