過去是用GCM 但firebase出來就有FCM
一直想要試試看FCM APP打訊息給APP，終於成功了!
之前自己架伺服器設webserverAPI，再讓Android去呼叫伺服器API
這次用Android內直接打fcm send，但這樣做法是不建議，因為金鑰暴露在外面...
後來想只是自己的小APP 玩玩而已就練練隨便寫
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compile 'com.squareup.okhttp3:okhttp:3.3.0'

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public static final MediaType JSON
        = MediaType.parse("application/json; charset=utf-8");

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new AsyncTask<Void, Void, Void>() {

    @Override
    protected Void doInBackground(Void... params) {
        try {
            OkHttpClient client = new OkHttpClient();
            JSONObject json = new JSONObject();
            JSONObject dataJson = new JSONObject();
            dataJson.put("body", "Hi this is sent from device to device");
            dataJson.put("title", "dummy title");
            json.put("notification", dataJson);
            json.put("to", "暫時寫自己的TOKEN測試用");
            RequestBody body = RequestBody.create(JSON, json.toString());
            Request request = new Request.Builder()
                    .header("Authorization", "key=AAAA0qHCG1g:APA91bEkkT.....JteHVBNbvc0h31xs3hAnq" )
                    .url("https://fcm.googleapis.com/fcm/send")
                    .post(body)
                    .build();
            Response response = client.newCall(request).execute();
            String finalResponse = response.body().string();
        } catch (Exception e) {
            //Log.d(TAG,e+"");
        }
        return null;
    }
    @Override
    protected void onPostExecute(
            Void result) {
    }
}.execute();

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注意:KEY是在

參考資料:

How to send device to device messages using Firebase Cloud Messaging?