How to create PDF layers with Foxit PDF SDK (Objective-C)

PDF Layers, in other words, Optional Content Groups (OCG), are supported in Foxit PDF SDK. Users can selectively view or hide the contents in different layers of a multi-layer PDF document. Multi-layers are widely used in many application domains such as CAD drawings, maps, layered artwork and multi-language document, etc.

In Foxit PDF SDK, a PDF layer is associated with a layer node. To retrieve a layer node, user should construct a PDF FSLayerTree object first and then call function FSLayerTree::getRootNode to get the root layer node of the whole layer tree. Furthermore, you can enumerate all the nodes in the layer tree from the root layer node. Foxit PDF SDK provides APIs to get/set layer data, view or hide the contents in different layers, set layers’ name, add or remove layers, and edit layers.

Example:

How to create a PDF layer

#include "FSPDFObjC.h"
...
// Assuming FSPDFDoc doc has been loaded.
...
FSLayerTree* layertree = [[FSLayerTree alloc] initWithDocument:doc];
FSLayerNode* root = [layertree getRootNode];
if ([root isEmpty]) {
    return -1;
}
...

How to set layer node information

#include "FSPDFObjC.h"
...
// Assuming FSPDFDoc doc has been loaded.
...
FSLayerTree* layertree = [[FSLayerTree alloc] initWithDocument:doc];
FSLayerNode* root = [layertree getRootNode];
if ([root isEmpty]) {
    return -1;
}
setAllLayerNodesInformation(root);
void setAllLayerNodesInformation(FSLayerNode* layer_node) {
    if ([layer_node hasLayer]) {
        [layer_node setDefaultVisible:YES];
        [layer_node setExportUsage:FSLayerTreeStateUndefined];
        [layer_node setViewUsage:FSLayerTreeStateOFF];
        FSLayerPrintData* print_data = [[FSLayerPrintData alloc] initWithSubtype:@"subtype_print" print_state:FSLayerTreeStateON];
        [layer_node setPrintUsage:print_data];
        FSLayerZoomData* zoom_data = [[FSLayerZoomData alloc] initWithMin_factor:1 max_factor:10];
        [layer_node setZoomUsage:zoom_data];
        NSString* new_name = [NSString stringWithFormat:@"%@%@",@"[View_OFF_Print_ON_Export_Undefined]", [layer_node getName]];
        [layer_node setName:new_name];
    }
    int count = [layer_node getChildrenCount];
    for (int i = 0; i < count; i++) {
        FSLayerNode* child = [layer_node getChild:i];
        setAllLayerNodesInformation(child);
    }
}
...

How to edit a layer tree

#include "FSPDFObjC.h"
...
FSLayerTree* layertree = [[FSLayerTree alloc] initWithDocument:doc];
FSLayerNode* root = [layertree getRootNode];
if ([root isEmpty]) {
    return -1;
}
int children_count = [root getChildrenCount];
[root removeChild:children_count-1];
FSLayerNode* child = [root getChild:children_count-2];
FSLayerNode* child0 = [root getChild:0];
[child moveTo:child0 index:0];
[child addChild:0 name:@"AddedLayerNode" has_Layer:YES];
[child addChild:0 name:@"AddedNode" has_Layer:NO];
...