One of the technical principles of the Android support library printing framework: overview (Translation: Technical Principles of Android Support Library Print Framework -Part 1: OverView)

The Android support library printing framework is a set of support libraries used on the Android platform for printing functions.It provides a set of APIs that can use these APIs to implement the printing function. The technical principles of the Android support library printing framework can be divided into the following parts: data preparation, printing layout and printing process. 1. Data preparation: Before printing, you need to prepare data to be printed.These data can be text, images or other types of content.Developers can use the Java code to obtain or generate these data.For example, you can read the content in a text file with the file class, or use the BitMap class to load a picture file. The following is an example of Java code that reads text file content: try { File file = new File("/storage/emulated/0/example.txt"); FileInputStream inputStream = new FileInputStream(file); int size = inputStream.available(); byte[] buffer = new byte[size]; inputStream.read(buffer); inputStream.close(); String textContent = new String(buffer, "UTF-8"); // Use textContent to print operation } catch (IOException e) { e.printStackTrace(); } 2. Print layout: Android support library printing framework uses XML layout files to describe the layout of the print content.Developers can create a print layout in a way similar to creating an Activity layout.Print layout files can contain text views, image views, and other types of views.Developers can specify the location, size and style attributes of each view.Print layout files are expressed in XML formats. You can use Android's layout resource files and Android interface construction tools to create and edit. The following is an example of a simple print layout, which contains a title and some print content: <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <TextView android:layout_width="match_parent" android:layout_height="wrap_content" Android: Text = "Print Title" android:textSize="24sp" android:gravity="center"/> <TextView android:layout_width="match_parent" android:layout_height="wrap_content" Android: text = "Print Content 1" android:textSize="16sp"/> <TextView android:layout_width="match_parent" android:layout_height="wrap_content" Android: text = "Print Content II" android:textSize="16sp"/> <!-Other views-> </LinearLayout> 3. Printing process: The printing process is the core part of the printing framework of the Android support library.Developers can use the printing process API to specify the settings and options of printing, and perform actual printing operations.The printing process includes the following steps: -Coloning printing tasks: Developers can use the Printmanager class to create a printing task and specify the name and ID of the printing. PrintManager printManager = (PrintManager) getSystemService(Context.PRINT_SERVICE); Printjob Printjob = Printmanager.print ("Print Mission Name", New MyPrintDocumentadapter (), NULL); -Coloning and configuration Printing file adapter: Developers need to create a printed file adapter class and implement the method.This adapter class is responsible for generating the content of the print document. private class MyPrintDocumentAdapter extends PrintDocumentAdapter { @Override public void onLayout(PrintAttributes oldAttributes, PrintAttributes newAttributes, CancellationSignal cancellationSignal, LayoutResultCallback layoutResultCallback, Bundle bundle) { // Implement the logic of printing layout, including setting page size and border distance, etc. } @Override public void onWrite(PageRange[] pageRanges, ParcelFileDescriptor fileDescriptor, CancellationSignal cancellationSignal, WriteResultCallback writeResultCallback) { // Realize the logic of writing the print content into the print file } } -The processed print results: When the printing task is successful or failed, you can register the status and results of the printing task by registering the PrintJobStateChangelistener. printJob.addPrintJobStateChangeListener(new PrintJobStateChangeListener() { @Override public void onPrintJobStateChanged(PrintJobId printJobId) { if (printJobInfo.getState() == PrintJob.STATE_COMPLETED) { // Print success } else if (printJobInfo.getState() == PrintJob.STATE_FAILED) { // Print failed } } }); To sum up, the Android support library printing framework implements the print function through three steps: data preparation, printing layout and printing process.Developers can write code in accordance with these technical principles to achieve custom printing functions.