使用 Wi-Fi Direct (P2P) 探索服務

本課程的第一堂課「使用網路服務探索功能」已說明如何探索連線至本機網路的服務。不過，使用 Wi-Fi Direct (P2P) 服務探索功能，您可以直接探索鄰近裝置的服務，而無須連線至網路。您也可以宣傳裝置上執行的服務。即使沒有可用的本機網路或無線基地台，這些功能仍可協助您在應用程式之間進行通訊。

雖然這組 API 的用途與上一課所述的網路服務探索 API 相似，但在程式碼中實作的方式卻截然不同。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，請在資訊清單中新增 CHANGE_WIFI_STATE、ACCESS_WIFI_STATE、ACCESS_FINE_LOCATION 和 INTERNET 權限。如果應用程式指定 Android 13 (API 級別 33) 以上版本，請一併將 NEARBY_WIFI_DEVICES 權限新增至資訊清單。雖然 Wi-Fi Direct 不需要網際網路連線，但會使用標準 Java 通訊端，因此在 Android 中使用這些通訊端需要要求權限。

<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 也必須啟用定位模式：

新增本機服務

如果您提供本機服務，就必須註冊該服務，以便進行服務探索。當您註冊本機服務後，架構會自動回應來自同儕的服務探索要求。

如要建立本機服務，請按照下列步驟操作：

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

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
            }
        });
    }

瀏覽附近的服務

Android 會使用回呼方法通知應用程式可用的服務，因此您首先要做的就是設定這些服務。建立 WifiP2pManager.DnsSdTxtRecordListener 以監聽收到的記錄。其他裝置可以選擇廣播這項記錄。收到訊息後，請將裝置位址和其他相關資訊複製到目前方法以外的資料結構中，以便日後存取。以下範例假設記錄包含「buddyname」欄位，並填入使用者的身分。

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。這個事件會接收實際的說明和連結資訊。先前的程式碼程式碼片段實作了 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個值，將 DNS 記錄連結至相應的服務資訊。實作兩個事件監聽器後，請使用 setDnsSdResponseListeners() 方法將事件監聽器新增至 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);
    ...
}

接著，建立服務要求並呼叫 addServiceRequest()。這個方法也會使用事件監聽器來回報成功或失敗。

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，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，恭喜你完成設定！如果遇到問題，請注意，您所做的非同步呼叫會將 WifiP2pManager.ActionListener 做為引數，並提供回呼，指出成功或失敗。如要診斷問題，請將偵錯程式碼放入 onFailure()。方法提供的錯誤代碼會暗示問題所在。以下是可能的錯誤值及其含義

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