setMethodCallHandler
- Flutter course
- Advanced
- Lesson 48/69
- 4 min
Receive native calls with setMethodCallHandler.
What is setMethodCallHandler?
setMethodCallHandler listens to method calls coming from the native side to Dart. When the native side calls a method, the registered callback runs. This allows Dart to receive communication initiated by the native side.
channel.setMethodCallHandler((call) async {
if (call.method == 'notify') {
print('Notification received');
}
});The MethodCall object
The handler callback takes a MethodCall object. You read the method name with call.method and the sent arguments with call.arguments. With this information you process the request from the native side.
channel.setMethodCallHandler((call) async {
print(call.method);
print(call.arguments);
});Practice Register a handler and trigger it
Create a MethodChannel, register a handler with setMethodCallHandler and print call.method inside the handler. Then trigger the handler with channel.simulateCall('notify'). Wait 10 milliseconds.
Starter code
class MethodCall {
final String method;
MethodCall(this.method);
}
class MethodChannel {
final String name;
void Function(MethodCall)? _handler;
MethodChannel(this.name);
void setMethodCallHandler(void Function(MethodCall) handler) {
_handler = handler;
}
void simulateCall(String method) {
if (_handler != null) _handler!(MethodCall(method));
}
}
void main() async {
// MethodChannel oluştur
// handler kaydet, call.method yazdır
// simulateCall ile tetikle
}Sample solution
class MethodCall {
final String method;
MethodCall(this.method);
}
class MethodChannel {
final String name;
void Function(MethodCall)? _handler;
MethodChannel(this.name);
void setMethodCallHandler(void Function(MethodCall) handler) {
_handler = handler;
}
void simulateCall(String method) {
if (_handler != null) _handler!(MethodCall(method));
}
}
void main() async {
const channel = MethodChannel('samples.flutter.dev/battery');
channel.setMethodCallHandler((call) {
print(call.method);
});
channel.simulateCall('notify');
await Future.delayed(Duration(milliseconds: 10));
}Expected output
notify
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 When does setMethodCallHandler fire?
- When Dart calls a native method
- When the native side calls a method on Dart Correct answer
- It never fires, it is for definition only
- Only when the app starts
Explanation: setMethodCallHandler fires when the native side calls a method on Dart; Dart calling native is done with invokeMethod.
2 Register a handler
channel.____((call) async {
print(call.method);
});channel.setMethodCallHandler((call) async {
print(call.method);
});Explanation: To listen to calls from the native side you call the setMethodCallHandler method and provide a callback.
3 setMethodCallHandler parts
| Term | Meaning |
|---|---|
setMethodCallHandler |
Registers a handler |
MethodCall |
Call object |
call.method |
Method name |
callback |
Handler function |