Linux-based Flutter method channel Channels

original

https://medium.com/flutter-community/using-flutter-method-channels-on-linux-2f6ae3e99653

Code

https://github.com/charafau/linux_method_channel

refer to

text

Flutter Method Channels on Linux

Linux-based Flutter method channel

meet again! Today I will continue my Flutter Linux journey, and we will touch Linux integration again. Last time we managed to set up Visual Studio Code for plug-in development, today we will further study Method Channels.

If you want to create a plug-in with method channel support, it is very simple, just use flutter create \-t plugin \--platforms=linux <name of your project> to generate a Flutter project from the template. But what if you don't want to create a separate plugin, just add some custom code to the Flutter Linux application? I found this is not easy, so I think I will write this article so that you don't have to solve it yourself.

In order not to delay any further, let's get started.

Create method channel

First, we need to create codecs codec , binary messenger binary messenger and channel. Next, we will assign a method call to the custom method, which we will create in the next step.

For this, let's open my my_application.cc . Cc in the linux folder and navigate to my my_application_activate function. Next, we implement the objects described above after the plugin is initialized.

In the example below, name_of_our_channel is the method we call from Dart code.

Callback

Now let's create a callback function:

Very simple, we pass a channel, methodcall and some user data.

To check for the channel’s method name we need to use the fl_method_call_get_name function on method_call object. And compare it with strcmp like so:

In order to check the method name of the channel, we need to use the fl_method_call_get_name function method_call Then compare it with strcmp , like this:

Method does not implement response

If the method passed to the channel does not exist, we need to return an unimplemented result to do this, we need to call fl_method_call_respond

Error handling

Before we start discussing parameters and custom results, let's take a quick look at error handling.

Fortunately, it is very similar to the unimplemented method:

We can see that it is almost the same, we just use fl_method_error_response_new create results, rather than fl_method_not_implemented_response_new .

Get Dart parameters

Okay, now it's time to write what we want to write from scratch. Let us suppose that we want to send data from Dart to C++. In order to do this, we only need to send a map from Dart, but how to get it?

To do this, we need to call fl_method_call_get_args(FlMethodCall) , which returns a pointer to FlValue .

Next we check whether the returned value is of the correct type:

In the above example, we are looking for strings, but there are others, such as int, float, bool, map. For the complete list check Flutter Engine Documentation

The same is true for type checking, check the entire list of enumerations to Documentation

Return some value

We are almost done, we managed to deal with unimplemented methods, errors and get parameters from methods. The rest is to return the value of Dart.

Fortunately for us, this is very similar to what we have already done, we just need to create FlMethodResponse and put FlValue into it. Below is an example:

As before, there is more value creation function of document links Link to More value for Documentation Creation function

Code completion + debugging

I think I should give you some rewards, because you are here, so I decided to write the code completion and debugging setup program in Visual Studio Code.

Before starting, you must install the C++ and Cmake plug-ins.

First let's set up the code completion. Create a file c_cpp_properties.json Json is in it. .vscode a 0614d2a2996b38 folder in the root directory of your project, and then put this configuration file into it:

Check the compiler path (Flutter uses Clang) and adjust the c/c++ standard as needed.

In order to set up debugging, we need to create a launch configuration .vscode folder launch.json Let's take a look at the configuration:

Very simple, but the binary name needs to be changed. Also, be aware that to make it work, you need to build your Flutter project with flutter run .