Flutter develops EventChannel for Android communication

• Android sends messages
• Note the following when sending messages on Android:
• Android gets the current phone battery
• The Flutter end receives messages

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Preface: In the previous chapter, we introduced BasicMessageChannel bidirectional communication, one of the hybrid Flutter development communications. In this chapter, we introduce the Event that Android sends messages to Flutter independently and continuously. The Flutter cannot send messages to Android and has no return value Channel

Let’s take a look at today’s results.

Rendering (1.1) :



Analysis:

The Android side:

• A Button, a Text()
• Text Displays the current power using the broadcast receiver

The Flutter end:

• Receive data from Android and display it

Android sends messages

Step 1: Create EventChannel

 private final EventChannel eventChannelPlugin;

 eventChannelPlugin = new EventChannel(messenger, "demo.ht.com.androidproject/EventChannelPlugin");
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• Parameter 1 :BinaryMessenger Messenger tool for sending messages
• Parameter 2 :String name Channel name Unique identifier (andRendering (1.2)Corresponding)

Rendering (1.2)

Second, send the message via setStreamHandler()

public class EventChannelPlugin implements EventChannel.StreamHandler {
	eventChannelPlugin.setStreamHandler(this);

	 @Override
    public void onListen(Object args, EventChannel.EventSink eventSink) {
        // To send a message
        eventSink.success(ElectricityQuantity);
    }

    @Override
    public void onCancel(Object o) {}}Copy the code

The message is sent by overriding the eventSink parameter in the onListen() method

Call eventsink.success (” Message to send, current is power “);

Complete code for EventChannelPlugin:

import io.flutter.plugin.common.BinaryMessenger;
import io.flutter.plugin.common.EventChannel;
/ * * * SZJ 2020/11/26 * CSDN blog: https://blog.csdn.net/weixin_44819566/ * WeChat public: code on rich * EventChannelPlugin * change for data flow (the event * For example: mobile phone battery change, network connection change, gyroscope, sensor, etc.; * /
public class EventChannelPlugin implements EventChannel.StreamHandler {
    private final String ElectricityQuantity;

    / * * * *@paramMessenger A tool for sending messages@paramElectricityQuantity Current quantity */
    public static void registerWith(BinaryMessenger messenger, String ElectricityQuantity) {
        new EventChannelPlugin(messenger, ElectricityQuantity);
    }

    private EventChannelPlugin(BinaryMessenger messenger,String ElectricityQuantity) {
        this.ElectricityQuantity = ElectricityQuantity;

        EventChannel eventChannelPlugin = new EventChannel(messenger, "demo.ht.com.androidproject/EventChannelPlugin");

        eventChannelPlugin.setStreamHandler(this);
    }
    @Override
    public void onListen(Object args, EventChannel.EventSink eventSink) {
        // To send a message
        eventSink.success(ElectricityQuantity);
    }

    @Override
    public void onCancel(Object o) {}}Copy the code

Note the following when sending messages on Android:

Android gets the current phone battery

I pasted the code from the Internet and shared it with you

IntentFilter = new IntentFilter(IntentFilter.ACTION_BATTERY_CHANGED); * receiver = new BatteryReceiver(textView); * registerReceiver(receiver, filter); * /
public class BatteryReceiver extends BroadcastReceiver {
    private TextView pow;

    public BatteryReceiver(TextView pow) {
        this.pow = pow;
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        int current = intent.getExtras().getInt("level");// Get the current power
        int total = intent.getExtras().getInt("scale");// Get the total power
        int percent = current * 100 / total;
        pow.setText(percent + "%"); }}Copy the code

Use: Just pass the textView object in.

 IntentFilter filter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
 receiver = new BatteryReceiver(textView);
 registerReceiver(receiver, filter);
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The Flutter end receives messages

  /// EventChannel receives the power sent by Android
  EventChannel _eventChannelPlugin = EventChannel("demo.ht.com.androidproject/EventChannelPlugin");
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	String _eventMessage; // To receive EventMes charge

	// Use Event to receive power messages
    _eventChannelPlugin.receiveBroadcastStream().listen((event) {
      setState(() {
	        _eventMessage = event;
      });
    });
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