android - 创建 GoogleApiClient 实例时出现 NullPointerException

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，现在我想在脸上展示手机电池。根据我研究后的理解，这只能通过消息或数据层 API 来实现。所以我开始在他的领域工作，但一开始我就遇到了问题。我无法连接到 Google Api 客户端。

我在“磨损”下有两个类 - 一个是 watch (服务)的通用类，另一个是我创建的:

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();
}

当我简单地像这样实例化它时:BatteryActivity batteryActivity = new BatteryActivity();我收到此错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Looper android.content.Context.getMainLooper()' on a null object reference

如果我实例化了，我不明白 mGoogleApiClient 为何为空。请注意 - 这完全基于此处的谷歌文档 - https://developer.android.com/training/wearables/data-layer/messages.html

Answer 1

我想您应该在 onCreate 方法上构建 GoogleApiClient。你的代码应该是这样的:

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();
    }
}