Android support library printing framework Seven: Printing data processing and conversion

Android support library printing framework technical principles 7: print data processing and conversion When printing operations on Android devices, data processing and conversion are very important steps.The Android support library printing framework provides a simple and powerful method to process and convey the printing data so that the required content can be presented correctly during the printing process. 1. Data processing: First, the data to be printed should be converted into a format suitable for printing.This includes processing text, images and other content so that it can be displayed correctly when printing.For example, if you want to print a piece of text, you can use the TextPaint class to format the text and convert it into an appropriate format in order to properly presented on the paper.Similarly, if you want to print the image, you can use the BitMap class to process the image and convert it to a format suitable for printing. 2. Data conversion: Once the data processing is completed, the processing data after processing is required to convert the data suitable for printing.The Android support library printing framework provides a Printdocumentadapter class that allows developers to convert the processed data into pages suitable for printing.The Printdocumentadapter class provides several important methods to implement data conversion, including onlyout (), onwrite (), and onfinish (). -Onlayout () method is used to determine the layout of the printing page.In this method, developers can specify the size and direction of the page and perform other related settings. @Override public void onLayout(PrintAttributes oldAttributes, PrintAttributes newAttributes, CancellationSignal cancellationSignal, LayoutResultCallback callback, Bundle extras) { // Specify the size and direction of the page PrintDocumentInfo.Builder builder = new PrintDocumentInfo.Builder("file name") .setContentType(PrintDocumentInfo.CONTENT_TYPE_DOCUMENT) .setPageCount(1); PrintDocumentInfo info = builder.build(); // The layout of the printing page of the notification system callback.onLayoutFinished(info, true); } -Onwrite () method is used to write the processed data into the printing page.In this method, developers can use Canvas class to draw text and images on the page, and set the appropriate page border distance, font size, etc. @Override public void onWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal, WriteResultCallback callback) { FileOutputStream output = new FileOutputStream(destination.getFileDescriptor()); // Create a Canvas object for drawing text and images PdfDocument.Page page = mPdfDocument.startPage(0); // Draw text and images on the page ... // Save the drawn content in the PDF file mPdfDocument.finishPage(page); mPdfDocument.writeTo(output); mPdfDocument.close(); // Complete writing callback.onWriteFinished(new PageRange[]{PageRange.ALL_PAGES}); } -Onfinish () method is used to clean up after the printing operation is completed.In this method, developers can close and release related resources. @Override public void onFinish() { // Clean up work ... } As mentioned above, data processing and conversion are an important part of the Android support library printing framework.Through appropriate data processing and conversion, developers can ensure that the printing operation can properly present the required content.The above part introduces some methods in the Printdocumentadapter class, and provides corresponding Java code example for reference for developers.