The key is to configure the following two parameters:
initialPreview, initialPreviewConfig, are arrays, one-to-one correspondence. You can preview the thumbnail when you modify it
'initialPreview'=>[
"http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/FullMoon2010.jpg/631px-FullMoon2010.jpg",
"http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Earth_Eastern_Hemisphere.jpg/600px-Earth_Eastern_Hemisphere.jpg"
],
'initialPreviewAsData'=>true,
'initialCaption'=>"The Moon and the Earth",
'initialPreviewConfig' => [
['caption' => 'Moon.jpg', 'size' => '873727'],
['caption' => 'Earth.jpg', 'size' => '1287883'],
],
echo FileInput::widget([
'name' => 'attachment_49[]',
'options'=>[
'multiple'=>true
],
'pluginOptions' => [
'initialPreview'=>[
"http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/FullMoon2010.jpg/631px-FullMoon2010.jpg",
"http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Earth_Eastern_Hemisphere.jpg/600px-Earth_Eastern_Hemisphere.jpg"
],
'initialPreviewAsData'=>true,
'initialCaption'=>"The Moon and the Earth",
'initialPreviewConfig' => [
['caption' => 'Moon.jpg', 'size' => '873727'],
['caption' => 'Earth.jpg', 'size' => '1287883'],
],
'overwriteInitial'=>false,
'maxFileSize'=>2800
]
]);