Add an API for Flutter

var _readOnly;

set readOnly(bool value) => _readOnly = value;

Config.fromJson(Map<String, dynamic> json) :
    _readOnly = json['readOnly'];

Map<String, dynamic> toJson() => {
    'readOnly': _readOnly,
};

First add the property to ios/Classes/PTFlutterDocumentController.h:

@property (nonatomic, assign, getter=isReadOnly) BOOL readOnly;

Define a config constant for the property in ios/Classes/PdftronFlutterPlugin.h:

// config
static NSString * const PTReadOnlyKey = @"readOnly";

In ios/Classes/PdftronFlutterPlugin.m, we iterate through the config and check for the presence of keys. Add the config constant that you defined in the previous step, and set the property:

+ (void)configureDocumentController:(PTFlutterDocumentController*)documentController withConfig:(NSString*)config
{
    ...            
    for (NSString* key in configPairs.allKeys) {
        if([key isEqualToString:PTDisabledToolsKey])
        {
            ...
        } else if ([key isEqualToString:PTReadOnlyKey]) {
            NSNumber* readOnlyNumber = [PdftronFlutterPlugin getConfigValue:configPairs configKey:PTReadOnlyKey class:[NSNumber class] error:&error];        
            if (!error && readOnlyNumber) {
                [documentController setReadOnly:[readOnlyNumber boolValue]];
            }
        }

In this case, we call the default setter. Sometimes a custom setter must be defined in ios/Classes/PTFlutterDocumentController.m.

In ios/Classes/PTFlutterDocumentController.m, give the property an initial value:

- (void)initViewerSettings
{
    _base64 = NO;
    _readOnly = NO;
    ...
}

In the same file, use the property to set the PTToolManager.readonly property.

- (void)viewWillLayoutSubviews
{
    [super viewWillLayoutSubviews];

    if (self.needsDocumentLoaded) {
        ...
    }
    
    if (![self.toolManager isReadonly] && self.readOnly) {
        self.toolManager.readonly = YES;
    }
    
    [self.plugin.tabbedDocumentViewController.tabManager saveItems];
}

Now the document associated with the PTPDFViewCtrl is read-only.

class Functions {
    static const getPageCropBox = "getPageCropBox";
}

Future<PTRect> getPageCropBox(int pageNumber) {
    return _channel.invokeMethod(Functions.getPageCropBox, <String, dynamic>{'pageNumber': pageNumber}).then((value) => jsonDecode(value));
}

static Future<PTRect> getPageCropBox(int pageNumber) {
    return _channel.invokeMethod(Functions.getPageCropBox, <String, dynamic>{'pageNumber': pageNumber}).then((value) => jsonDecode(value));
}

class PTRect {
  double x1, y1, x2, y2, width, height;
  PTRect(this.x1, this.y1, this.x2, this.y2, this.width, this.height);

  factory PTRect.fromJson(dynamic json) {
    return PTRect(getDouble(json['x1']), getDouble(json['y1']), getDouble(json['x2']), getDouble(json['y2']), getDouble(json['width']), getDouble(json['height']));
  }

  // a helper for JSON number decoding
  static getDouble(dynamic value) {
    if (value is int) {
      return value.toDouble();
    } else {
      return value;
    }
  }
}

First, define the function and argument constants in ios/Classes/PdftronFlutterPlugin.h:

// function
static NSString * const PTGetPageCropBoxKey = @"getPageCropBox";
...

// argument
static NSString * const PTPageNumberArgumentKey = @"pageNumber";
...

Sometimes the argument constants may already exist, so check before you define any constants.

Open the ios/Classes/PdftronFlutterPlugin.m file and add a new case for the new function to handleMethodCall:

- (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
    if ([call.method isEqualToString:PTGetPlatformVersionKey]) {
        ...
    } else if ([call.method isEqualToString:PTGetPageCropBoxKey]) {
        NSNumber *pageNumber = [PluginUtils PT_idAsNSNumber:call.arguments[PTPageNumberArgumentKey]];
        [self getPageCropBox:pageNumber resultToken:result];
    } else {
        ...
    }
}

In the same file ios/Classes/PdftronFlutterPlugin.m, implement the new function:

- (void)getPageCropBox:(NSNumber *)pageNumber resultToken:(FlutterResult)result
{
    PTDocumentViewController *docVC = [self getDocumentViewController];

    if(documentController.document == Nil)
    {
        // something is wrong, no document.
        NSLog(@"Error: The document view controller has no document.");
        flutterResult([FlutterError errorWithCode:@"get_page_crop_box" message:@"Failed to get page crop box" details:@"Error: The document view controller has no document."]);
        return;
    }

    NSError *error;
    [docVC.pdfViewCtrl DocLock:YES withBlock:^(PTPDFDoc * _Nullable doc) {
        if([doc HasDownloader])
        {
            // too soon
            NSLog(@"Error: The document is still being downloaded.");
            return;
        }
        
        PTPage *page = [doc GetPage:(int)pageNumber];
        if (page) {
            PTPDFRect *rect = [page GetCropBox];
            NSDictionary<NSString *, NSNumber *> *map = @{
                PTX1Key: @([rect GetX1]),
                PTY1Key: @([rect GetY1]),
                PTX2Key: @([rect GetX2]),
                PTY2Key: @([rect GetY2]),
                PTWidthKey: @([rect Width]),
                PTHeightKey: @([rect Height]),
            };
            NSData *jsonData = [NSJSONSerialization dataWithJSONObject:map options:0 error:nil];
            NSString *res = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
            
            result(res);
        }

    } error:&error];
    
    if(error)
    {
        NSLog(@"Error: There was an error while trying to get the page crop box. %@", error.localizedDescription);
    }
}

The logic is to first get the current document view controller, lock the file and check whether the document is still being downloaded. If not, get the crop box and encode all the associated information into a JSON string as the result.

The actual implementation will depend on the actual functionality.

const _zoomChangedChannel = const EventChannel('zoom_changed_event');

typedef void ZoomChangedListener(dynamic zoom);

enum eventSinkId {
    zoomChangedId,
}

CancelListener startZoomChangedListener(ZoomChangedListener listener) {
  var subscription = _zoomChangedChannel
      .receiveBroadcastStream(eventSinkId.zoomChangedId.index)
      .listen(listener, cancelOnError: true);

  return () {
    subscription.cancel();
  };
}

In ios/Classes/PdftronFlutterPlugin.h do the following:

• add an event key constant.
• add an id to the enum eventSinkId.
• add a method to the existing PdftronFlutterPlugin interface.

By the end of the guide, this method will send events to Dart and will be called whenever zoom changes.

// event strings
static NSString * const PTZoomChangedEventKey = @"zoom_changed_event";

typedef enum {
    ...
    zoomChangedId,
} EventSinkId;

@interface PdftronFlutterPlugin : NSObject<FlutterPlugin, FlutterStreamHandler, FlutterPlatformView>

-(void)documentController:(PTDocumentController *)docVC zoomChanged:(NSNumber*)zoom;

@end

In order to send events to Flutter, we need an event channel and sink.

Add a new event sink property to ios/Classes/PdftronFlutterPlugin.m:

@interface PdftronFlutterPlugin () <PTTabbedDocumentViewControllerDelegate, PTDocumentControllerDelegate>
...
@property (nonatomic, strong) FlutterEventSink zoomChangedEventSink;
...
@end

In the same file, declare and initialize the event channel:

- (void)registerEventChannels:(NSObject<FlutterBinaryMessenger> *)messenger
{
    ...
    FlutterEventChannel* zoomChangedEventChannel = [FlutterEventChannel eventChannelWithName:PTZoomChangedEventKey binaryMessenger:messenger];
    ...
    [zoomChangedEventChannel setStreamHandler:self];
}

The two methods below, onListenWithArguments:eventSink: and onCancelWithArguments:eventSink:, are used to start and cancel the event listener respectively.

In the same file, add a case for our event id to each method:

- (FlutterError* _Nullable)onListenWithArguments:(id _Nullable)arguments eventSink:(FlutterEventSink)events
{
    
    int sinkId = [arguments intValue];
    
    switch (sinkId)
    {
        ...
        case zoomChangedId:
            self.zoomChangedEventSink = events;
            break;
    }

    return Nil;
}

- (FlutterError* _Nullable)onCancelWithArguments:(id _Nullable)arguments
{
    int sinkId = [arguments intValue];
    
    switch (sinkId)
    {
         ...
        case zoomChangedId:
            self.zoomChangedEventSink = nil;
            break;
    }

    return Nil;
}

In the same file, ios/Classes/PdftronFlutterPlugin.m, implement the method to send the event to Dart, using the new event sink:

#pragma mark - EventSinks
-(void)documentController:(PTDocumentController *)docVC zoomChanged:(NSNumber*)zoom
{
    if (self.zoomChangedEventSink != nil)
    {
        self.zoomChangedEventSink(zoom);
    }
}

In the next step, we will call this method whenever the event occurs.

The PTPDFViewCtrlDelegate protocol contains the method pdfViewCtrl:pdfScrollViewDidZoom:. This method allows adopting delegates to respond to the PTPDFViewCtrl class when the zoom event occurs.

Implement this method in ios/Classes/PTFlutterDocumentController.m:

- (void)pdfViewCtrl:(PTPDFViewCtrl*)pdfViewCtrl pdfScrollViewDidZoom:(UIScrollView *)scrollView
{
    const double zoom = self.pdfViewCtrl.zoom * self.pdfViewCtrl.zoomScale;
    [self.plugin documentController:self zoomChanged:[NSNumber numberWithDouble:zoom]];
}

var config = Config();
config.readOnly = true;

await PdftronFlutter.openDocument("https://pdftron.s3.amazonaws.com/downloads/pl/PDFTRON_mobile_about.pdf", config: config);

var cropBox = await PdftronFlutter.getPageCropBox(1);
print('The width of crop box for page 1 is: ' + cropBox.width.toString());

var zoomChangedCancel = startZoomChangedListener((zoom) {
    print("flutter zoom changed. Current zoom is: $zoom");
});

zoomChangedCancel(); // Cancels the listener

var config = Config();
config.readOnly = true;

await controller.openDocument("https://pdftron.s3.amazonaws.com/downloads/pl/PDFTRON_mobile_about.pdf", config: config);

var cropBox = await controller.getPageCropBox(1);
print('The width of crop box for page 1 is: ' + cropBox.width.toString());

var zoomChangedCancel = startZoomChangedListener((zoom) {
    print("flutter zoom changed. Current zoom is: $zoom");
});

zoomChangedCancel(); // Cancels the listener

If you're only developing for iOS, then you're all done!

If you're also deploying on Android, you'll need to complete the necessary steps for Android.

If you're developing for both iOS and Android, please consider submitting a PR, as upstreaming the change will simplify your developing and make the APIs available for other Apryse customers.