Question

我已经开始为Android Wear创建Watch Face。我已经实现了几乎所有的东西，现在我想在脸上显示手机电池。根据我在研究后的理解，这只能通过Message或Data Layer API实现。所以我开始在他所在地区工作，但我一开始就遇到了问题。我无法连接到Google Api客户端。

我有两个课程＆＃34;穿＆＃34; - 手表（服务）的一个通用和我创建的通用：

public class BatteryActivity extends Activity {

    GoogleApiClient mGoogleApiClient = new GoogleApiClient.Builder(this)
        .addConnectionCallbacks( new ConnectionCallbacks() {
            @Override
            public void onConnected(Bundle connectionHint) {
                Log.i( "", "onConnected: " + connectionHint);
                // Now you can use the Data Layer API
            }
            @Override
            public void onConnectionSuspended(int cause) {
                Log.i( "", "onConnectionSuspended: " + cause);
            }
        })
        .addOnConnectionFailedListener( new OnConnectionFailedListener() {
            @Override
            public void onConnectionFailed(ConnectionResult result) {
                Log.i( "", "onConnectionFailed: " + result);
            }
        })
                // Request access only to the Wearable API
        .addApi(Wearable.API)
        .build();
}

我只是像这样实例：BatteryActivity batteryActivity = new BatteryActivity(); 我收到这个错误：

java.lang.NullPointerException：尝试调用虚方法＆＃39; android.os.Looper android.content.Context.getMainLooper（）＆＃39;在null 对象参考

如果我实例化的话，我不明白mGoogleApiClient是如何为空的。作为一个注释 - 这纯粹基于谷歌文档 - https://developer.android.com/training/wearables/data-layer/messages.html

Answer 1

我想你应该在onCreate方法上构建GoogleApiClient。你的代码是这样的：

public class BatteryActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_layout);

        GoogleApiClient mGoogleApiClient = new GoogleApiClient.Builder(this)
            .addConnectionCallbacks( new ConnectionCallbacks() {
                @Override
                public void onConnected(Bundle connectionHint) {
                    Log.i( "", "onConnected: " + connectionHint);
                    // Now you can use the Data Layer API
                }
                @Override
                public void onConnectionSuspended(int cause) {
                    Log.i( "", "onConnectionSuspended: " + cause);
                }
            })
            .addOnConnectionFailedListener( new OnConnectionFailedListener() {
                @Override
                public void onConnectionFailed(ConnectionResult result) {
                    Log.i( "", "onConnectionFailed: " + result);
                }
            })
        // Request access only to the Wearable API
        .addApi(Wearable.API)
        .build();
    }
}

Answer 2

It also happens when not providing proper context. Pass context like this :

mGoogleApiClient = new GoogleApiClient.Builder(context) // Pass context here
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API).build();

Answer 3

理想情况下，这应该通过异步任务完成：https://developer.android.com/google/auth/api-client.html#Communicating

private class WatchTask extends AsyncTask<String, Void, Void> {
    protected void doInBackground(String text) {

或者为了快速解决问题，您可能只是在错误的位置使用它：

在onCreate使用getActivity()或this中使用Context代替此行：

GoogleApiClient mGoogleApiClient = new GoogleApiClient.Builder(this)

我还建议退房：http://developer.android.com/training/wearables/data-layer/index.html

如果你真的想要使用某个活动，那么它看起来像是：

public class MainActivity extends Activity  implements
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener, MessageApi.MessageListener {

    private GoogleApiClient googleClient; // A google client for Wear interaction

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Build a new GoogleApiClient that includes the Wearable API
        googleClient = new GoogleApiClient.Builder(this)
                .addApi(Wearable.API)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .build();
    }

    @Override
    public void onConnected(Bundle connectionHint) {
        Wearable.MessageApi.addListener(googleClient, this);
    }

    @Override
    public void onMessageReceived(MessageEvent messageEvent) {
        //Same onMessageReceived as in WearableListenerService
    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) { }
    @Override
    public void onConnectionSuspended(int i) { }
}

创建GoogleApiClient实例时出现NullPointerException

3 个答案: