flipper/docs/extending/create-plugin.md

---
id: create-plugin
title: Client Plugin API
---

## FlipperPlugin
To build a client plugin, just implement the `FlipperPlugin` interface.

The ID that is returned from your implementation needs to match the `name` defined in your JavaScript counterpart's `package.json`.


<!--DOCUSAURUS_CODE_TABS-->
<!--Android-->
```java
public class MyFlipperPlugin implements FlipperPlugin {
  private FlipperConnection mConnection;

  @Override
  public String getId() {
    return "MyFlipperPlugin";
  }

  @Override
  public void onConnect(FlipperConnection connection) throws Exception {
    mConnection = connection;
  }

  @Override
  public void onDisconnect() throws Exception {
    mConnection = null;
  }

  @Override
  public boolean runInBackground() {
  	return false;
  }
}
```
<!--iOS-->
```objective-c
@interface MyFlipperPlugin : NSObject<FlipperPlugin>
@end

@implementation MyFlipperPlugin

- (NSString*)identifier { return @"MyFlipperPlugin"; }
- (void)didConnect:(FlipperConnection*)connection {}
- (void)didDisconnect {}
- (BOOL)runInBackground {}

@end
```
<!--C++-->
```c++
class MyFlipperPlugin : public FlipperPlugin {
public:
  std::string identifier() const override { return "MyFlipperPlugin"; }
  void didConnect(std::shared_ptr<FlipperConnection> conn) override;
  void didDisconnect() override;
  bool runInBackground() override;
};
```
<!--END_DOCUSAURUS_CODE_TABS-->


## Using FlipperConnection

`onConnect` will be called when your plugin becomes active. This will provide a `FlipperConnection` allowing you to register receivers for desktop method calls and respond with data.

<!--DOCUSAURUS_CODE_TABS-->
<!--Android-->
```java
connection.receive("getData", new FlipperReceiver() {
  @Override
  public void onReceive(FlipperObject params, FlipperResponder responder) throws Exception {
    responder.success(
        new FlipperObject.Builder()
            .put("data", MyData.get())
            .build());
  }
});
```
<!--iOS-->
```objective-c
@interface MyFlipperPlugin : NSObject<FlipperPlugin>
@end

@implementation MyFlipperPlugin

- (NSString*)identifier { return @"MyFlipperPlugin"; }

- (void)didConnect:(FlipperConnection*)connection
{
  [connection receive:@"getData" withBlock:^(NSDictionary *params, FlipperResponder *responder) {
    [responder success:@{
      @"data":[MyData get],
    }];
  }];
}

- (void)didDisonnect {}

@end
```
<!--C++-->
```c++
void MyFlipperPlugin::didConnect(std::shared_ptr<FlipperConnection> conn) {
  conn->receive("getData", [](const folly::dynamic &params,
                             std::unique_ptr<FlipperResponder> responder) {
    dynamic response = folly::dynamic::object("data", getMyData());
    responder->success(response);
  });
}
```
<!--END_DOCUSAURUS_CODE_TABS-->

## Push data to the desktop

You don't have to wait for the desktop to request data though, you can also push data directly to the desktop. If the JS plugin subscribes to the same method, it will receive the data.

<!--DOCUSAURUS_CODE_TABS-->
<!--Android-->
```java
connection.send("MyMessage",
    new FlipperObject.Builder()
        .put("message", "Hello")
        .build()
```
<!--iOS-->
```objective-c
[connection send:@"getData" withParams:@{@"message":@"hello"}];
```
<!--C++-->
```c++
void MyFlipperPlugin::didConnect(std::shared_ptr<FlipperConnection> conn) {
  dynamic message = folly::dynamic::object("message", "hello");
  conn->send("getData", message);
}
```
<!--END_DOCUSAURUS_CODE_TABS-->

## Background Plugins

In some cases you may want to provide data to flipper even when your plugin is not currently active. Returning true in `runInBackground()` will result in `onConnect` being called as soon as Flipper connects, and allow you to use the connection at any time.

This should be used in combination with a `persistedStateReducer` on the desktop side. See the [JS Plugin API](js-plugin-api#background-plugins) for details.

The benefit is that the desktop plugin can process this data in the background and fire notifications. It also reduces the number of renders and time taken to display the data when the plugin becomes active.