Hosting native Android views in your Flutter app with Platform Views

Platform views allow you to embed native views in a Flutter app, so you can apply transforms, clips, and opacity to the native view from Dart.

This allows you, for example, to use the native Google Maps from the Android SDK directly inside your Flutter app.

Flutter supports two modes: Virtual displays and Hybrid composition.

Which one to use depends on the use case. Let’s take a look:

  • Virtual displays render the android.view.View instance to a texture, so it’s not embedded within the Android Activity’s view hierachy. Certain platform interactions such as keyboard handling and accessibility features might not work.

  • Hybrid composition appends the native android.view.View to the view hierarchy. Therefore, keyboard handling, and accessibility work out of the box. Prior to Android 10, this mode might significantly reduce the frame throughput (FPS) of the Flutter UI. See performance for more info.

To create a platform view on Android, use the following steps:

On the Dart side

On the Dart side, create a Widget and add the following build implementation:

In your Dart file, for example native_view_example.dart, use the following instructions:

  1. Add the following imports:

    import 'package:flutter/foundation.dart';
    import 'package:flutter/gestures.dart';
    import 'package:flutter/material.dart';
    import 'package:flutter/rendering.dart';
    import 'package:flutter/services.dart';
  2. Implement a build() method:

    Widget build(BuildContext context) {
      // This is used in the platform side to register the view.
      const String viewType = '<platform-view-type>';
      // Pass parameters to the platform side.
      const Map<String, dynamic> creationParams = <String, dynamic>{};
    
      return PlatformViewLink(
        viewType: viewType,
        surfaceFactory:
            (context, controller) {
          return AndroidViewSurface(
            controller: controller as AndroidViewController,
            gestureRecognizers: const <Factory<OneSequenceGestureRecognizer>>{},
            hitTestBehavior: PlatformViewHitTestBehavior.opaque,
          );
        },
        onCreatePlatformView: (params) {
          return PlatformViewsService.initSurfaceAndroidView(
            id: params.id,
            viewType: viewType,
            layoutDirection: TextDirection.ltr,
            creationParams: creationParams,
            creationParamsCodec: const StandardMessageCodec(),
            onFocus: () {
              params.onFocusChanged(true);
            },
          )
            ..addOnPlatformViewCreatedListener(params.onPlatformViewCreated)
            ..create();
        },
      );
    }

For more information, see the API docs for:

Virtual Display

In your Dart file, for example native_view_example.dart, use the following instructions:

  1. Add the following imports:

    import 'package:flutter/material.dart';
    import 'package:flutter/services.dart';
  2. Implement a build() method:

    Widget build(BuildContext context) {
      // This is used in the platform side to register the view.
      const String viewType = '<platform-view-type>';
      // Pass parameters to the platform side.
      final Map<String, dynamic> creationParams = <String, dynamic>{};
    
      return AndroidView(
        viewType: viewType,
        layoutDirection: TextDirection.ltr,
        creationParams: creationParams,
        creationParamsCodec: const StandardMessageCodec(),
      );
    }

For more information, see the API docs for:

On the platform side

On the platform side, use the standard io.flutter.plugin.platform package in either Java or Kotlin:

In your native code, implement the following:

Extend io.flutter.plugin.platform.PlatformView to provide a reference to the android.view.View, For example, NativeView.kt:

package dev.flutter.example

import android.content.Context
import android.graphics.Color
import android.view.View
import android.widget.TextView
import io.flutter.plugin.platform.PlatformView

internal class NativeView(context: Context, id: Int, creationParams: Map<String?, Any?>?) : PlatformView {
    private val textView: TextView

    override fun getView(): View {
        return textView
    }

    override fun dispose() {}

    init {
        textView = TextView(context)
        textView.textSize = 72f
        textView.setBackgroundColor(Color.rgb(255, 255, 255))
        textView.text = "Rendered on a native Android view (id: $id)"
    }
}

Create a factory class that creates an instance of the NativeView created earlier, for example, NativeViewFactory.kt:

package dev.flutter.example

import android.content.Context
import android.view.View
import io.flutter.plugin.common.StandardMessageCodec
import io.flutter.plugin.platform.PlatformView
import io.flutter.plugin.platform.PlatformViewFactory

class NativeViewFactory : PlatformViewFactory(StandardMessageCodec.INSTANCE) {
    override fun create(context: Context, viewId: Int, args: Any?): PlatformView {
        val creationParams = args as Map<String?, Any?>?
        return NativeView(context, viewId, creationParams)
    }
}

Finally, register the platform view. You can do this in an app or a plugin.

For app registration, modify the app’s main activity (for example, MainActivity.kt):

package dev.flutter.example

import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine

class MainActivity : FlutterActivity() {
    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        flutterEngine
                .platformViewsController
                .registry
                .registerViewFactory("<platform-view-type>", NativeViewFactory())
    }
}

For plugin registration, modify the plugin’s main class (for example, PlatformViewPlugin.kt):

package dev.flutter.plugin.example

import io.flutter.embedding.engine.plugins.FlutterPlugin
import io.flutter.embedding.engine.plugins.FlutterPlugin.FlutterPluginBinding

class PlatformViewPlugin : FlutterPlugin {
    override fun onAttachedToEngine(binding: FlutterPluginBinding) {
        binding
                .platformViewRegistry
                .registerViewFactory("<platform-view-type>", NativeViewFactory())
    }

    override fun onDetachedFromEngine(binding: FlutterPluginBinding) {}
}

In your native code, implement the following:

Extend io.flutter.plugin.platform.PlatformView to provide a reference to the android.view.View, For example, NativeView.java:

package dev.flutter.example;

import android.content.Context;
import android.graphics.Color;
import android.view.View;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import io.flutter.plugin.platform.PlatformView;
import java.util.Map;

class NativeView implements PlatformView {
   @NonNull private final TextView textView;

    NativeView(@NonNull Context context, int id, @Nullable Map<String, Object> creationParams) {
        textView = new TextView(context);
        textView.setTextSize(72);
        textView.setBackgroundColor(Color.rgb(255, 255, 255));
        textView.setText("Rendered on a native Android view (id: " + id + ")");
    }

    @NonNull
    @Override
    public View getView() {
        return textView;
    }

    @Override
    public void dispose() {}
}

Create a factory class that creates an instance of the NativeView created earlier, for example, NativeViewFactory.java:

package dev.flutter.example;

import android.content.Context;
import androidx.annotation.Nullable;
import androidx.annotation.NonNull;
import io.flutter.plugin.common.StandardMessageCodec;
import io.flutter.plugin.platform.PlatformView;
import io.flutter.plugin.platform.PlatformViewFactory;
import java.util.Map;

class NativeViewFactory extends PlatformViewFactory {

  NativeViewFactory() {
    super(StandardMessageCodec.INSTANCE);
  }

  @NonNull
  @Override
  public PlatformView create(@NonNull Context context, int id, @Nullable Object args) {
    final Map<String, Object> creationParams = (Map<String, Object>) args;
    return new NativeView(context, id, creationParams);
  }
}

Finally, register the platform view. You can do this in an app or a plugin.

For app registration, modify the app’s main activity (for example, MainActivity.java):

package dev.flutter.example;

import androidx.annotation.NonNull;
import io.flutter.embedding.android.FlutterActivity;
import io.flutter.embedding.engine.FlutterEngine;

public class MainActivity extends FlutterActivity {
    @Override
    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
        flutterEngine
            .getPlatformViewsController()
            .getRegistry()
            .registerViewFactory("<platform-view-type>", new NativeViewFactory());
    }
}

For plugin registration, modify the plugin’s main file (for example, PlatformViewPlugin.java):

package dev.flutter.plugin.example;

import androidx.annotation.NonNull;
import io.flutter.embedding.engine.plugins.FlutterPlugin;

public class PlatformViewPlugin implements FlutterPlugin {
  @Override
  public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
    binding
        .getPlatformViewRegistry()
        .registerViewFactory("<platform-view-type>", new NativeViewFactory());
  }

  @Override
  public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {}
}

For more information, see the API docs for:

Finally, modify your build.gradle file to require one of the minimal Android SDK versions:

android {
    defaultConfig {
        minSdkVersion 19 // if using Hybrid composition.
        minSdkVersion 20 // if using Virtual display.
    }
}

Performance

Platform views in Flutter come with performance trade-offs.

For example, in a typical Flutter app, the Flutter UI is composed on a dedicated raster thread. This allows Flutter apps to be fast, as the main platform thread is rarely blocked.

While a platform view is rendered with Hybrid composition, the Flutter UI is composed from the platform thread, which competes with other tasks like handling OS or plugin messages.

Prior to Android 10, Hybrid composition copied each Flutter frame out of the graphic memory into main memory, and then copied it back to a GPU texture. In Android 10 or above, the graphics memory is copied twice. As this copy happens per frame, the performance of the entire Flutter UI may be impacted.

Virtual display, on the other hand, makes each pixel of the native view flow through additional intermediate graphic buffers, which cost graphic memory and drawing performance.

For complex cases, there are some techniques that can be used to mitigate these issues.

For example, you could use a placeholder texture while an animation is happening in Dart. In other words, if an animation is slow while a platform view is rendered, then consider taking a screenshot of the native view and rendering it as a texture.

For more information, see: