Flutter plugin插件开发获取Activity对象

在开发Flutter插件的时候有一个Android端的方法调用的时候需要传入Activity对象，可通过如下方法获取

1. 先保存registerWith方法的PluginRegistry.Registrarca参数
2. 然后通过PluginRegistry.Registrarca的activity()方法来获取Activity对象

如下示例代码

public class MyPlugin implements MethodChannel.MethodCallHandler {

    private static PluginRegistry.Registrar registrar;

    public static void registerWith(PluginRegistry.Registrar registrar) {
        // 先保存Registrar对象
        MyPlugin.registrar = registrar;
        MethodChannel channel = new MethodChannel(registrar.messenger(), "MyPlugin");
        channel.setMethodCallHandler(new MyPlugin());
    }

    @Override
    public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) {
        if ("run".equals(methodCall.method)) {
            // 通过Registrar对象获取Activity
            Puppy.run(registrar.activity());
        }
    }
}

如下为Registrar接口的定义，可以知道通过Registrar不仅可以获取Activity对象，还可以通过context()获取Context上下文对象，通过view()获取FlutterView对象等，其他方法有需要用到的可以自行去了解下

public interface Registrar {
    Activity activity();

    Context context();

    Context activeContext();

    BinaryMessenger messenger();

    TextureRegistry textures();

    PlatformViewRegistry platformViewRegistry();

    FlutterView view();

    String lookupKeyForAsset(String var1);

    String lookupKeyForAsset(String var1, String var2);

    PluginRegistry.Registrar publish(Object var1);

    PluginRegistry.Registrar addRequestPermissionsResultListener(PluginRegistry.RequestPermissionsResultListener var1);

    PluginRegistry.Registrar addActivityResultListener(PluginRegistry.ActivityResultListener var1);

    PluginRegistry.Registrar addNewIntentListener(PluginRegistry.NewIntentListener var1);

    PluginRegistry.Registrar addUserLeaveHintListener(PluginRegistry.UserLeaveHintListener var1);

    PluginRegistry.Registrar addViewDestroyListener(PluginRegistry.ViewDestroyListener var1);
}