PDF Printing Causes app loading forever on MacOS

[Mu7ammadRasul]

when i try to print the pdf on macOS the app loads and the only solution is to force quit the app, have i done something wrong or its not possible to feature this on macOS?

[kketanssharma]

same for me

[sabin26]

Same issue, the app hangs on macOS and I have to force quit the app. Upon debugging this line is the culprit but it used to work before. Though, I have updated the flutter version to latest stable.

await Printing.layoutPdf(onLayout: (final _) async => pdfBytes);

[sabin26]

This seems to be a duplicate of #1865

The solution for the provided issue:

Hey you can fix by adding info.plist by disable merge thread changes

	<key>FLTEnableMergedPlatformUIThread</key>
        <false/>

Or You

printing_ffi you can use this plugin which uses ffi rather than platform channel for performance.

[Mu7ammadRasul]

This seems to be a duplicate of #1865

The solution for the provided issue:

Hey you can fix by adding info.plist by disable merge thread changes

	<key>FLTEnableMergedPlatformUIThread</key>
        <false/>

Or You
printing_ffi you can use this plugin which uses ffi rather than platform channel for performance.

should this be on the macOS's info.plist or IOS?

[sabin26]

On the platform (macos/ios)'s info.plist, where you are experiencing the issue.

[muzipiao]

On macOS, when using Printing.layoutPdf(onLayout:), if you do not explicitly set dynamicLayout: false, a deadlock occurs and the UI freezes, preventing users from printing or previewing PDFs (No similar issue observed on iOS).

Temporary Solution

You must pass the parameter dynamicLayout: false when invoking the method:

await Printing.layoutPdf(
  onLayout: (PdfPageFormat format) => pdfFile.readAsBytesSync(),
  dynamicLayout: false,
);

Deadlock Cause Analysis

At line 66 of printing/macos/Classes/PrintJob.swift, the code uses semaphore.wait() to block the main thread, waiting for the Dart layer to generate PDF data. Since both the Flutter plugin and the Dart MethodChannel also run on the main thread, the main thread is locked and cannot asynchronously receive the PDF data.

The official role of the dynamicLayout parameter:

When dynamicLayout is enabled, [onLayout] will be called when the user changes the printer or settings.

Relevant Code Snippet

if dynamic {
    printing.onLayout( ... )
    semaphore.wait() // Block the main thread, waiting for a document
}

Related code link