TYPO3 StandaloneView not finding Templates

Question

I am using the StandaloneView to output some data.

The problem I encountered is that the given TemplateRootPath is just ignored.
TYPO3 throws an exception saying that it looked for the template in /typo3/public/typo3conf/ext//Resources/Private/Templates/ but the given TemplateRootPath is one folder further down in /printView/.

Maybe there is something that went over my head but I am looking for a fix for about one and a half hours now.

$standaloneView = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Fluid\View\StandaloneView::class);
$standaloneView->setLayoutRootPaths([
    \TYPO3\CMS\Core\Utility\GeneralUtility::getFileAbsFileName('EXT:<my-extension>/Resources/Private/Layouts/printView/'),
]);
$standaloneView->setPartialRootPaths([
    \TYPO3\CMS\Core\Utility\GeneralUtility::getFileAbsFileName('EXT:<my-extension>/Resources/Private/Partials'),
]);
$standaloneView->setTemplateRootPaths([
    \TYPO3\CMS\Core\Utility\GeneralUtility::getFileAbsFileName('EXT:<my-extension>/Resources/Private/Templates/printView/'),
]);
$standaloneView->setFormat('html');
$standaloneView->setTemplate('printView/printView');
$standaloneView->assignMultiple([
    //variable assignment
]);

echo $standaloneView->render(); 

<my-extension> is there on purpose

Answer 1

set...RootPaths(...) expects an array as parameter.

Maybe you need to change the filename of the template to UpperCamelCase.
That might not be needed for the parameter you use for selection, but the generated filename will have it. ( PrintView.html instead of printView.html )