java GoogleApiClient 空指针异常

GoogleApiClient null pointer exception

提问by Roman Pozdnyakov

I try to learn android development and now i developing an app with fused location service.

我尝试学习 android 开发，现在我开发了一个带有融合位置服务的应用程序。

I got a RunFragment.java class when i want to put the GoogleMap fragment, Textviews with latitude and longitude and some other widgets. First of all i want to connect to GoogleApiClient and i created new class that will do all this job and leave RunFragment.java clear. (Is that a good idea??) When i try to run my app i got this error:

当我想放置 GoogleMap 片段、带有纬度和经度的 Textviews 以及其他一些小部件时，我得到了一个 RunFragment.java 类。首先，我想连接到 GoogleApiClient，我创建了一个新的类来完成所有这些工作并让 RunFragment.java 保持清晰。（这是个好主意吗？？）当我尝试运行我的应用程序时，出现此错误：

     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Looper android.content.Context.getMainLooper()' on a null object reference
        at com.google.android.gms.common.api.GoogleApiClient$Builder.<init>(Unknown Source)
        at com.runtheworld.roman.runtheworld.GoogleAPI.buildGoogleApiClient(GoogleAPI.java:28)
        at com.runtheworld.roman.runtheworld.RunFragment.onCreate(RunFragment.java:39)
        at android.app.Fragment.performCreate(Fragment.java:2031)

There is the relevant classes:

有相关的类：

RunFragment.java

运行Fragment.java

package com.runtheworld.roman.runtheworld;

import android.app.Fragment;
import android.os.Bundle;
import android.view.InflateException;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;



public class RunFragment extends Fragment  {

private static View view;

// TextViews
TextView lat,lon;

// GoogleApi
private GoogleAPI mGoogleApiClient = new GoogleAPI(getActivity());



// Default Constructor
public RunFragment() {
}


@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    mGoogleApiClient.buildGoogleApiClient();
}
@Override
public void onStart(){
    super.onStart();
    mGoogleApiClient.Connect();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    if (view != null) {
        ViewGroup parent = (ViewGroup) view.getParent();
        if (parent != null)
            parent.removeView(view);
    }
    try {
        view = inflater.inflate(R.layout.run_fragment, container, false);
    } catch (InflateException e) {
        // Map already created
    }

    lat = (TextView)view.findViewById(R.id.lat);
    lon = (TextView)view.findViewById(R.id.lon);
    lat.setText(String.valueOf(mGoogleApiClient.getLat()));
    lon.setText(String.valueOf(mGoogleApiClient.getLon()));


    return view;
}




}

GoogleAPI.java

谷歌API.java

package com.runtheworld.roman.runtheworld;


import android.content.Context;
import android.location.Location;
import android.os.Bundle;
import android.util.Log;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.location.LocationServices;

public class GoogleAPI  implements GoogleApiClient.ConnectionCallbacks,    GoogleApiClient.OnConnectionFailedListener {

private Context context;
private GoogleApiClient mGoogleApiClient;
private boolean isConnected;
// Location
Location mLastLocation;

public GoogleAPI(Context c) {
    context = c;
}


protected synchronized void buildGoogleApiClient() {
    Log.d("MYTAG", "BUILDING GOOGLE API");
    mGoogleApiClient = new GoogleApiClient.Builder(context)
            .addConnectionCallbacks(this)
            .addOnConnectionFailedListener(this)
            .addApi(LocationServices.API)
            .build();
}

public boolean Connect(){
    if (!mGoogleApiClient.isConnected())
        mGoogleApiClient.connect();
    else
    Log.d("MYTAG","GoogleApiClient is already connected!");
    return isConnected;
}

@Override
public void onConnected(Bundle bundle) {
    Log.d("MYTAG", "GOOGLE API CONNECTED!");
    mLastLocation = LocationServices.FusedLocationApi.getLastLocation(
            mGoogleApiClient);
    if (mLastLocation != null) {
    }
}

public double getLat(){
    return mLastLocation.getLatitude();
}
public double getLon(){
    return mLastLocation.getLongitude();
}
@Override
public void onConnectionSuspended(int i) {

}

@Override
public void onConnectionFailed(ConnectionResult connectionResult) {

}

}

Can anyone help ?

任何人都可以帮忙吗？

采纳答案by Daniel Nugent

It sounds like your initial problem was fixed in the comments, here is how you can complete the functionality.

听起来您最初的问题已在评论中解决，以下是您如何完成功能。

First, to fix the NPE, make sure that mLocationis not null before you reference it:

首先，要修复 NPE，请mLocation在引用它之前确保它不为 null：

public double getLat(){
    double retVal = 0d;
    if (mLastLocation != null){
       retVal = mLastLocation.getLatitude();
    }
    return retVal;
}
public double getLon(){
    double retVal = 0d;
    if (mLastLocation != null){
       retVal = mLastLocation.getLongitude();
    }
    return retVal;
}

The next problem is that getLastLocation()has a high tendency to return null.

下一个问题是很有可能getLastLocation()返回 null。

The best way to get around that is to register a location listener.

解决这个问题的最好方法是注册一个位置监听器。

Declare GoogleAPIas a location listener:

声明GoogleAPI为位置侦听器：

public class GoogleAPI  implements GoogleApiClient.ConnectionCallbacks,    GoogleApiClient.OnConnectionFailedListener, LocationListener{

private Context context;
private GoogleApiClient mGoogleApiClient;
private boolean isConnected;

Then register a listener in onConnected()(see documentation: for how to set up the values for minTime, fastestTime, and distanceThreshold):

然后注册一个监听器onConnected()（参见资料：关于如何设置的值minTime，fastestTime和distanceThreshold）：

        @Override
        public void onConnected(Bundle bundle) {
            Log.d("MYTAG", "GOOGLE API CONNECTED!");
            mLastLocation = LocationServices.FusedLocationApi.getLastLocation(
                    mGoogleApiClient);
            if (mLastLocation == null) {
               mLocationRequest = new LocationRequest();
               mLocationRequest.setInterval(minTime);
               mLocationRequest.setFastestInterval(fastestTime);
                                 mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
              mLocationRequest.setSmallestDisplacement(distanceThreshold);
              LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
            }

        }

Then add the location changed callback:

然后添加位置更改回调：

 @Override
    public void onLocationChanged(Location location) {

             mLastLocation = location;

     }