使用 Wi-Fi Direct (P2P) 探索服務

本課程的第一課「使用網路服務探索」會說明如何探索連線至區域網路的服務。不過,使用 Wi-Fi Direct (P2P) 服務探索時,您不必連線到網路,就能直接探索鄰近裝置的服務。您也可以通告裝置上執行的服務。即使沒有區域網路或無線基地台,這些功能仍可協助在應用程式之間進行通訊。

雖然這組 API 的用途與前一堂課程所述的 Network Service Discovery API 類似,但實作時在程式碼中卻是截然不同的。本課程將說明如何使用 Wi-Fi Direct 探索其他裝置提供的服務。本課程假設您已熟悉 Wi-Fi Direct API。

設定資訊清單

如要使用 Wi-Fi P2P,請在資訊清單中加入 CHANGE_WIFI_STATEACCESS_WIFI_STATEACCESS_FINE_LOCATIONINTERNET 權限。如果應用程式指定的是 Android 13 (API 級別 33) 以上版本,請一併在資訊清單中加入 NEARBY_WIFI_DEVICES 權限。雖然 Wi-Fi Direct 不需要網際網路連線,卻使用標準 Java 通訊端,而在 Android 中使用這類通訊端需要取得要求的權限。

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.android.nsdchat"
    ...

    <uses-permission
        android:required="true"
        android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission
        android:required="true"
        android:name="android.permission.CHANGE_WIFI_STATE"/>
    <uses-permission
        android:required="true"
        android:name="android.permission.INTERNET"/>
    <!-- If your app targets Android 13 (API level 33)
         or higher, you must declare the NEARBY_WIFI_DEVICES permission. -->
    <uses-permission
        android:name="android.permission.NEARBY_WIFI_DEVICES"
        <!-- If your app derives location information from Wi-Fi APIs,
             don't include the "usesPermissionFlags" attribute. -->
        android:usesPermissionFlags="neverForLocation" />
    <uses-permission
        android:required="true"
        android:name="android.permission.ACCESS_FINE_LOCATION"
        <!-- If any feature in your app relies on precise location information,
             don't include the "maxSdkVersion" attribute. -->
        android:maxSdkVersion="32" />
    ...

除了上述權限以外,下列 API 也需要啟用位置模式:

新增本機服務

如果您提供本機服務,則必須註冊該服務,才能探索服務。本機服務註冊完成後,架構會自動回應來自對等互連的服務探索要求。

如要建立「本機」服務,請按照下列指示操作:

  1. 建立 WifiP2pServiceInfo 物件。
  2. 填入服務的相關資訊。
  3. 呼叫 addLocalService() 來註冊本機服務,以便進行服務探索。

Kotlin

    private fun startRegistration() {
        //  Create a string map containing information about your service.
        val record: Map<String, String> = mapOf(
                "listenport" to SERVER_PORT.toString(),
                "buddyname" to "John Doe${(Math.random() * 1000).toInt()}",
                "available" to "visible"
        )

        // Service information.  Pass it an instance name, service type
        // _protocol._transportlayer , and the map containing
        // information other devices will want once they connect to this one.
        val serviceInfo =
                WifiP2pDnsSdServiceInfo.newInstance("_test", "_presence._tcp", record)

        // Add the local service, sending the service info, network channel,
        // and listener that will be used to indicate success or failure of
        // the request.
        manager.addLocalService(channel, serviceInfo, object : WifiP2pManager.ActionListener {
            override fun onSuccess() {
                // Command successful! Code isn't necessarily needed here,
                // Unless you want to update the UI or add logging statements.
            }

            override fun onFailure(arg0: Int) {
                // Command failed.  Check for P2P_UNSUPPORTED, ERROR, or BUSY
            }
        })
    }

Java

    private void startRegistration() {
        //  Create a string map containing information about your service.
        Map record = new HashMap();
        record.put("listenport", String.valueOf(SERVER_PORT));
        record.put("buddyname", "John Doe" + (int) (Math.random() * 1000));
        record.put("available", "visible");

        // Service information.  Pass it an instance name, service type
        // _protocol._transportlayer , and the map containing
        // information other devices will want once they connect to this one.
        WifiP2pDnsSdServiceInfo serviceInfo =
                WifiP2pDnsSdServiceInfo.newInstance("_test", "_presence._tcp", record);

        // Add the local service, sending the service info, network channel,
        // and listener that will be used to indicate success or failure of
        // the request.
        manager.addLocalService(channel, serviceInfo, new ActionListener() {
            @Override
            public void onSuccess() {
                // Command successful! Code isn't necessarily needed here,
                // Unless you want to update the UI or add logging statements.
            }

            @Override
            public void onFailure(int arg0) {
                // Command failed.  Check for P2P_UNSUPPORTED, ERROR, or BUSY
            }
        });
    }

探索附近的服務

Android 採用回呼方法,向應用程式通知可用的服務,因此請先完成相關設定。建立 WifiP2pManager.DnsSdTxtRecordListener 來監聽收到的記錄。可選擇由其他裝置播送這個記錄。收到這些資訊後,請將裝置位址和任何其他相關資訊複製到目前方法以外的資料結構中,方便日後存取。以下範例假設記錄包含「buddyname」欄位,且已填入使用者身分。

Kotlin

private val buddies = mutableMapOf<String, String>()
...
private fun discoverService() {
    /* Callback includes:
     * fullDomain: full domain name: e.g. "printer._ipp._tcp.local."
     * record: TXT record dta as a map of key/value pairs.
     * device: The device running the advertised service.
     */
    val txtListener = DnsSdTxtRecordListener { fullDomain, record, device ->
        Log.d(TAG, "DnsSdTxtRecord available -$record")
        record["buddyname"]?.also {
            buddies[device.deviceAddress] = it
        }
    }
}

Java

final HashMap<String, String> buddies = new HashMap<String, String>();
...
private void discoverService() {
    DnsSdTxtRecordListener txtListener = new DnsSdTxtRecordListener() {
        @Override
        /* Callback includes:
         * fullDomain: full domain name: e.g. "printer._ipp._tcp.local."
         * record: TXT record dta as a map of key/value pairs.
         * device: The device running the advertised service.
         */

        public void onDnsSdTxtRecordAvailable(
                String fullDomain, Map record, WifiP2pDevice device) {
                Log.d(TAG, "DnsSdTxtRecord available -" + record.toString());
                buddies.put(device.deviceAddress, record.get("buddyname"));
            }
        };
}

如要取得服務資訊,請建立 WifiP2pManager.DnsSdServiceResponseListener。這會接收實際的說明和連線資訊。先前的程式碼片段會實作 Map 物件,將裝置位址與好友名稱配對。服務回應事件監聽器會使用這項資訊來連結 DNS 記錄與對應的服務資訊。實作兩個事件監聽器後,請使用 setDnsSdResponseListeners() 方法將其新增至 WifiP2pManager

Kotlin

private fun discoverService() {
    ...

    val servListener = DnsSdServiceResponseListener { instanceName, registrationType, resourceType ->
        // Update the device name with the human-friendly version from
        // the DnsTxtRecord, assuming one arrived.
        resourceType.deviceName = buddies[resourceType.deviceAddress] ?: resourceType.deviceName

        // Add to the custom adapter defined specifically for showing
        // wifi devices.
        val fragment = fragmentManager
                .findFragmentById(R.id.frag_peerlist) as WiFiDirectServicesList
        (fragment.listAdapter as WiFiDevicesAdapter).apply {
            add(resourceType)
            notifyDataSetChanged()
        }

        Log.d(TAG, "onBonjourServiceAvailable $instanceName")
    }

    manager.setDnsSdResponseListeners(channel, servListener, txtListener)
    ...
}

Java

private void discoverService() {
...

    DnsSdServiceResponseListener servListener = new DnsSdServiceResponseListener() {
        @Override
        public void onDnsSdServiceAvailable(String instanceName, String registrationType,
                WifiP2pDevice resourceType) {

                // Update the device name with the human-friendly version from
                // the DnsTxtRecord, assuming one arrived.
                resourceType.deviceName = buddies
                        .containsKey(resourceType.deviceAddress) ? buddies
                        .get(resourceType.deviceAddress) : resourceType.deviceName;

                // Add to the custom adapter defined specifically for showing
                // wifi devices.
                WiFiDirectServicesList fragment = (WiFiDirectServicesList) getFragmentManager()
                        .findFragmentById(R.id.frag_peerlist);
                WiFiDevicesAdapter adapter = ((WiFiDevicesAdapter) fragment
                        .getListAdapter());

                adapter.add(resourceType);
                adapter.notifyDataSetChanged();
                Log.d(TAG, "onBonjourServiceAvailable " + instanceName);
        }
    };

    manager.setDnsSdResponseListeners(channel, servListener, txtListener);
    ...
}

現在建立服務要求並呼叫 addServiceRequest()。這個方法也會運用事件監聽器回報成功或失敗。

Kotlin

        serviceRequest = WifiP2pDnsSdServiceRequest.newInstance()
        manager.addServiceRequest(
                channel,
                serviceRequest,
                object : WifiP2pManager.ActionListener {
                    override fun onSuccess() {
                        // Success!
                    }

                    override fun onFailure(code: Int) {
                        // Command failed.  Check for P2P_UNSUPPORTED, ERROR, or BUSY
                    }
                }
        )

Java

        serviceRequest = WifiP2pDnsSdServiceRequest.newInstance();
        manager.addServiceRequest(channel,
                serviceRequest,
                new ActionListener() {
                    @Override
                    public void onSuccess() {
                        // Success!
                    }

                    @Override
                    public void onFailure(int code) {
                        // Command failed.  Check for P2P_UNSUPPORTED, ERROR, or BUSY
                    }
                });

最後,請呼叫 discoverServices()

Kotlin

        manager.discoverServices(
                channel,
                object : WifiP2pManager.ActionListener {
                    override fun onSuccess() {
                        // Success!
                    }

                    override fun onFailure(code: Int) {
                        // Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
                        when (code) {
                            WifiP2pManager.P2P_UNSUPPORTED -> {
                                Log.d(TAG, "Wi-Fi Direct isn't supported on this device.")
                            }
                        }
                    }
                }
        )

Java

        manager.discoverServices(channel, new ActionListener() {

            @Override
            public void onSuccess() {
                // Success!
            }

            @Override
            public void onFailure(int code) {
                // Command failed.  Check for P2P_UNSUPPORTED, ERROR, or BUSY
                if (code == WifiP2pManager.P2P_UNSUPPORTED) {
                    Log.d(TAG, "Wi-Fi Direct isn't supported on this device.");
                else if(...)
                    ...
            }
        });

如果一切順利,太好了,這樣就大功告成了!如果遇到問題,請記得您執行的非同步呼叫會將 WifiP2pManager.ActionListener 做為引數,並提供指出成功或失敗的回呼。如要診斷問題,請在 onFailure() 中加入偵錯程式碼。問題方法提示提供的錯誤代碼。以下是可能的錯誤值和意義

P2P_UNSUPPORTED
執行應用程式的裝置不支援 Wi-Fi Direct。
BUSY
系統忙於處理要求,
ERROR
發生內部錯誤,因此作業失敗。