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Add an API

Add an API for React Native


The PDFTron iOS React Native API includes all of the most used functions and methods for viewing, annotating and saving PDF documents. However, it is possible your app may need access to APIs that are available as part of the native API, but are not directly available to React Native.

This guide provides an example of how to add the following to the React Native interface:

  • pageChangeOnTap prop that determines whether page will turn left or right when tapping corresponding edges.
  • getField function which retrieves information about a field using its name.
  • onLayoutChanged event listener that is raised when the layout of viewer has changed.

You can follow the same pattern to add new functions and props that your React Native app may need. The new additions could be simple ones, which expose one piece of functionality, or custom ones, that expose a series of native commands under the hood.

Prior to following this guide, we highly recommend you to go through the official guide here: Native UI Components to have a better understanding of the system.

1. Fork and clone PDFTron's React Native Repo

The source is hosted on GitHub here:

Fork the project and clone a copy of the repository to your disk.

Adding the pageChangeOnTap prop

2. Add prop to DocumentView.js interface file

The DocumentView.js interface file lists all of the React Native props on the DocumentView component.

Add the prop declaration:

static propTypes = {
  pageChangeOnTap: PropTypes.bool,

3. Define a ReactProp matches the JS declaration

Open file ios/RNTPTDocumentViewManager.m.

Add the method key that matches the JS declaration:

    if (json) {
        view.pageChangeOnTap = [RCTConvert BOOL:json];

4. Implement the methods to set the property

Open the ios/RNTPTDocumentView.h interface file and add a new property to the RNTPTDocumentView class:

@interface RNTPTDocumentView


@property (nonatomic, assign) BOOL pageChangeOnTap;



Open the ios/RNTPTDocumentView.m implementation file, and add the property setter:

- (void)setPageChangeOnTap:(BOOL)pageChangeOnTap
    _pageChangeOnTap = pageChangeOnTap;
    if (self.documentViewController) {
        [self applyViewerSettings];

In this case, we call the applyViewerSettings method and access the changesPageOnTap property to complete our implementation:

- (void)applyViewerSettings

    // Page change on tap.
    self.documentViewController.changesPageOnTap = self.pageChangeOnTap;


The actual implementation will depend on the actual functionality.

Adding the getField function

2. Add function to DocumentView.js interface file

The DocumentView.js interface file lists all of the React Native functions on the DocumentView component.

Add the function declaration:

getField = (fieldName) => {
    const tag = findNodeHandle(this._viewerRef);
    if(tag != null) {
      return DocumentViewManager.getField(tag, fieldName);
    return Promise.resolve();

3. Add method to module

The JS name of the new method is getField and the native method is getFieldForDocumentViewTag:fieldname:.

In ios/RNTPTDocumentViewModule.m, use the RCT_REMAP_METHOD macro to expose the native method to JS and simultaneously specify the JS name of the method.

                 getFieldForDocumentViewTag:(nonnull NSNumber *)tag
                 fieldName:(NSString *)fieldName
    @try {
        NSDictionary *field = [[self documentViewManager] getFieldForDocumentViewTag:tag fieldName:fieldName];
    @catch (NSException *exception) {
        reject(@"set_value_for_fields", @"Failed to set value on fields", [self errorFromException:exception]);

4. Implement the native method

Add the native method to ios/RNTPTDocumentViewManager.h:

- (NSDictionary *)getFieldForDocumentViewTag:(NSNumber *)tag fieldName:(NSString *)fieldName;

Implement the native method in ios/RNTPTDocumentViewManager.m:

- (NSDictionary *)getFieldForDocumentViewTag:(NSNumber *)tag fieldName:(NSString *)fieldName
    RNTPTDocumentView *documentView = self.documentViews[tag];
    if (documentView) {
        return [documentView getField:fieldName];
    } else {
        @throw [NSException exceptionWithName:NSInvalidArgumentException reason:@"Unable to get field for tag" userInfo:nil];
        return nil;

5. Implement the helper method

Add the following to ios/RNTPTDocumentView.h:

- (NSDictionary *)getField:(NSString *)fieldName;

Implement the method in ios/RNTPTDocumentView.m:

- (NSDictionary *)getField:(NSString *)fieldName
    PTPDFViewCtrl *pdfViewCtrl = self.currentDocumentViewController.pdfViewCtrl;
    if (!pdfViewCtrl) {
        return nil;
    NSMutableDictionary <NSString *, NSObject *> *fieldMap = [[NSMutableDictionary alloc] init];

    NSError *error;
    [pdfViewCtrl DocLockReadWithBlock:^(PTPDFDoc * _Nullable doc) {
        PTField *field = [doc GetField:fieldName];
        if (field && [field IsValid]) {
            PTFieldType fieldType = [field GetType];
            NSString* typeString;
            if (fieldType == e_ptbutton) {
                typeString = PTFieldTypeButtonKey;
            } else if (fieldType == e_ptcheck) {
                typeString = PTFieldTypeCheckboxKey;
                [fieldMap setValue:[[NSNumber alloc] initWithBool:[field GetValueAsBool]] forKey:PTFormFieldValueKey];
            } else if (fieldType == e_ptradio) {
                typeString = PTFieldTypeRadioKey;
                [fieldMap setValue:[field GetValueAsString] forKey:PTFormFieldValueKey];
            } else if (fieldType == e_pttext) {
                typeString = PTFieldTypeTextKey;
                [fieldMap setValue:[field GetValueAsString] forKey:PTFormFieldValueKey];
            } else if (fieldType == e_ptchoice) {
                typeString = PTFieldTypeChoiceKey;
                [fieldMap setValue:[field GetValueAsString] forKey:PTFormFieldValueKey];
            } else if (fieldType == e_ptsignature) {
                typeString = PTFieldTypeSignatureKey;
            } else {
                typeString = PTFieldTypeUnknownKey;
            [fieldMap setValue:typeString forKey:PTFormFieldTypeKey];
            [fieldMap setValue:fieldName forKey:PTFormFieldNameKey];
    } error:&error];
    if (error) {
        NSLog(@"Error: There was an error while trying to get field. %@", error.localizedDescription);
    return [[fieldMap allKeys] count] == 0 ? nil : fieldMap;

The logic is to get the PDF view controller and if the field names are valid, use the controller to get the fields from the current document.

Adding the onLayoutChanged event listener

2. Define the new listener in JS

Event listeners are handled in DocumentView.js. Add the following to the file:

static propTypes = {
    onLayoutChanged: PropTypes.func,

onChange = (event) => {
    if (event.nativeEvent.onLeadingNavButtonPressed) {
    } else if (event.nativeEvent.onLayoutChanged) {
      if (this.props.onLayoutChanged) {

The onLayoutChanged event listener does not require any arguments. If your event listener requires arguments, access them using event.nativeEvent.exampleArg.

3. Send event to JS

Add the following protocol method to ios/RNTPTDocumentView.h:

@protocol RNTPTDocumentViewDelegate <NSObject>
- (void)layoutChanged:(RNTPTDocumentView *)sender; 

Implement the protocol method in ios/RNTPTDocumentViewManager.m, under the Events pragma mark. Notice that we call RNTPTDocumentView's RCTBubblingEventBlock onChange event handler block, which will call the callback prop in JS.

#pragma mark - Events
- (void)layoutChanged:(RNTPTDocumentView *)sender
    if (sender.onChange) {
            @"onLayoutChanged" : @"onLayoutChanged",

4. Call layoutChanged protocol method in iOS

In step 3, we implemented the protocol method layoutChanged to send events to JS, but we haven't used it yet.

Add the following protocol method to ios/DocumentViewController/RNTPTDocumentViewController.h:

@protocol RNTPTDocumentBaseViewControllerDelegate <PTToolManagerDelegate>
- (void)rnt_documentViewControllerLayoutDidChange:(PTDocumentBaseViewController *)documentViewController;

Implement this protocol method in ios/RNTPTDocumentView.m, under the RNTPTDocumentViewControllerDelegate pragma mark. This is where we use layoutChanged.

#pragma mark - <RNTPTDocumentViewControllerDelegate>
- (void)rnt_documentViewControllerLayoutDidChange:(PTDocumentBaseViewController *)documentViewController
    if ([self.delegate respondsToSelector:@selector(layoutChanged:)]) {
        [self.delegate layoutChanged:self];

5. Receive layout changes from PDFViewCtrl

The PTPDFViewCtrlDelegate protocol contains the method pdfViewCtrlOnLayoutChanged. This method allows adopting delegates to respond to the PTPDFViewCtrl class when page layout has changed.

Implement pdfViewCtrlOnLayoutChanged in the following files:

  • ios/DocumentViewController/RNTPTDocumentViewController.m
  • ios/DocumentViewController/RNTPTDocumentController.m
  • ios/DocumentViewController/RNTPTCollaborationDocumentViewController.m
  • ios/DocumentViewController/RNTPTCollaborationDocumentController.m
#pragma mark - <PTPDFViewCtrlDelegate>
- (void)pdfViewCtrlOnLayoutChanged:(PTPDFViewCtrl *)pdfViewCtrl
    if ([self.delegate respondsToSelector:@selector(rnt_documentViewControllerLayoutDidChange:)]) {
        [self.delegate rnt_documentViewControllerLayoutDidChange:self];

The actual implementation will depend on the actual functionality.

Finishing steps

1. Push the code and integrate the updated source

Now npm install your forked version to your application.

The new functionality is now ready to use.

2. Access the new functionality

The app can now access the new API as follows:

onDocumentLoaded = () => {
    this._viewer.getField('someFieldName').then((field) => {
        if (field !== undefined) {
            console.log('field name:', field.fieldName);
            console.log('field value:', field.fieldValue);
            console.log('field type:', field.fieldType);

onLayoutChanged = () => {
    console.log("Layout changed");

    ref={(c) => this._viewer = c}

3. All done!

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 PDFTron customers.

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