android - 使用 PrintDocumentAdapter 和 PrintManager 更改页数

Question

我正在扩展 PrintDocumentAdapter 以通过云打印将名册信息发送到打印机。一切都运行良好，直到更改设置以使文档中的页数减少。

例如，一张表格适合两张 A4 页，但需要三张 A5 页。云打印开始时默认选择 A4，并生成预览。如果页面尺寸更改为 A5，则会按预期生成包含三页的新预览。如果随后将页面尺寸更改回 A4，云打印会显示消息“抱歉，这不起作用。请重试。”并且必须退出。

这似乎正在发生:

• onLayout() 使用 A4 文档属性调用。 LayoutResultCallback.onLayoutFinished() 传递一个设置为 2 的 PrintDocumentInfo pageCount。
• 按照预期，使用 0-1 的单个 PageRange 调用 onWrite()。
• 我将纸张尺寸更改为 A5。
• onLayout() 使用 A5 文档属性调用。 LayoutResultCallback.onLayoutFinished() 传递的 PrintDocumentInfo pageCount 设置为 3。
• 使用 0-1 的单个 PageRange 调用 onWrite()，这是旧范围
• 第二次调用 onWrite()，正确的 PageRange 为 0-2。

只有当旧的 PageRange 大于返回的页数时，才会导致错误，但为什么 onWrite() 会使用无效的 PageRange 被调用呢？

我注意到我的设备上的许多应用程序只是缩放输出，以便页数在不同设置之间不会发生变化。他们这样做是因为这个问题吗？

public class PrintAdapter extends PrintDocumentAdapter {

    private static final String TAG = "PrintAdapter";

    private PrintedPdfBuilder mPrintedPdfBuilder;
    private int mPages;

    public PrintAdapter(PrintedPdfBuilder printedPdfBuilder) {
        mPrintedPdfBuilder = printedPdfBuilder;
    }

    @Override
    public void onLayout(PrintAttributes oldAttributes, PrintAttributes newAttributes,
                         CancellationSignal cancellationSignal, LayoutResultCallback callback,
                         Bundle extras) {

        Log.v(TAG, "onLayout");
        // Respond to cancellation request
        if (cancellationSignal.isCanceled()) {
            callback.onLayoutCancelled();
            return;
        }

        int pages = mPrintedPdfBuilder.getPageCount(newAttributes);
        Log.v(TAG, "page count = " + pages);
        if (pages > 0) {
            // Return print information to print framework
            PrintDocumentInfo info = new PrintDocumentInfo
                    .Builder("print_output.pdf")
                    .setContentType(PrintDocumentInfo.CONTENT_TYPE_DOCUMENT)
                    .setPageCount(pages)
                    .build();
            // Content layout reflow is complete
            callback.onLayoutFinished(info, mPages != pages);
            mPages = pages;
        } else {
            // Otherwise report an error to the print framework
            callback.onLayoutFailed("Page count calculation failed.");
        }
    }

    @Override
    public void onWrite(PageRange[] ranges, ParcelFileDescriptor destination,
                        CancellationSignal cancellationSignal, WriteResultCallback callback) {

        Log.v(TAG, "onWrite() ranges: " + Arrays.toString(ranges));
        // Write PDF document to file
        try {
            PrintedPdfDocument pdf = mPrintedPdfBuilder.generateDocument(ranges);

            // check for cancellation
            if (cancellationSignal.isCanceled()) {
                callback.onWriteCancelled();
                mPrintedPdfBuilder.close();
                return;
            }
            pdf.writeTo(new FileOutputStream(destination.getFileDescriptor()));
        } catch (IOException e) {
            callback.onWriteFailed(e.toString());
            return;
        } finally {
            mPrintedPdfBuilder.close();
        }

        PageRange[] writtenPages = mPrintedPdfBuilder.getWrittenPages();
        Log.v(TAG, "writtenPages: " + Arrays.toString(writtenPages));
        // Signal the print framework the document is complete
        callback.onWriteFinished(writtenPages);
    }
}

日志猫:

08-28 11:46:44.187 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: onLayout
08-28 11:46:44.276 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: page count = 2
08-28 11:46:44.298 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: onWrite() ranges: [PageRange[0 - 1]]
08-28 11:46:44.512 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: writtenPages: [PageRange[0 - 1]]
08-28 11:46:50.418 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: onLayout
08-28 11:46:50.499 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: page count = 3
08-28 11:46:50.509 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: onWrite() ranges: [PageRange[0 - 1]]
08-28 11:46:50.678 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: writtenPages: [PageRange[0 - 1]]
08-28 11:46:50.918 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: onWrite() ranges: [PageRange[0 - 2]]
08-28 11:46:51.160 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: writtenPages: [PageRange[0 - 2]]
08-28 11:47:34.983 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: onLayout
08-28 11:47:35.049 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: page count = 2
08-28 11:47:35.056 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: onWrite() ranges: [PageRange[0 - 2]]
08-28 11:47:35.248 9714-9714/com.meremammal.www.staffrosterwizard V/PrintAdapter: writtenPages: [PageRange[0 - 1]]

每次设置更改时都会调用 onLayout，但由于某种原因，然后会使用之前的 PageRange[] 调用 onWrite

Answer 1

我捕获了 NullPointerException 错误并向用户显示一条重试消息。这将捕获错误并向用户显示您的消息以及“重试”按钮，该按钮随后会成功，因为 pageRanges 已更新。

    @Override
    public void onWrite(final PageRange[] pageRanges,
                        final ParcelFileDescriptor destination,
                        final CancellationSignal cancellationSignal,
                        final WriteResultCallback callback) {
        // Iterate over each page of the document,
        // check if it's in the output range.
        int requestedPageCount;
        for (int i = 0; i < mTotalPages; i++) {
            // Check to see if this page is in the output range.
            if (containsPage(pageRanges, i)) {
                //########## Add in this Try Catch Block   #############
                try {
                //######################################################
                    PdfDocument.PageInfo newPage = new PdfDocument.PageInfo.Builder(mPageWidth,
                            mPageHeight, i).create();
                    PdfDocument.Page page =
                            mPDFDocument.startPage(newPage);
                    if (cancellationSignal.isCanceled()) {
                        callback.onWriteCancelled();
                        mPDFDocument.close();
                        mPDFDocument = null;
                        return;
                    }
                    if (mPrintJobType == PrintType.LIST) {
                        drawPageList(page, i + 1, (mPageWidth < mPageHeight));
                    } else {
                        drawPageDetail(page, i);
                    }
                    mPDFDocument.finishPage(page);
                //######## Catch the error here and display a message
                } catch (NullPointerException e) {
                    //Catch a known error thrown thrown by pageRanges not being updated in a timely manner.
                    callback.onWriteFailed("We found a bug in the Android operating system. " +
                            "Please click Retry to continue.");
                    return;
                }
                //##################################################
            }
        }

        // Write PDF document to file
        try {
            mPDFDocument.writeTo(new FileOutputStream(
                    destination.getFileDescriptor()));
        } catch (IOException e) {
            callback.onWriteFailed(e.toString());
            return;
        } finally {
            mPDFDocument.close();
            mPDFDocument = null;
        }
        callback.onWriteFinished(pageRanges);
    }