尝试将数据从子活动返回到 MainActivity 时获取 NullPointerException
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【中文标题】尝试将数据从子活动返回到 MainActivity 时获取 NullPointerException【英文标题】：Getting a NullPointerException while trying to return data from a sub-activity to MainActivity 【发布时间】：2016-06-28 07:52:31 【问题描述】：我正在尝试实现一个启动子 Activity 的 android 应用程序，它将计算我当前位置的坐标。但是，在尝试将数据发送回 MainActivity 时，我的 onActivityResult 方法中出现 NullPointerException。这是两个类：
主要活动
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.location.Location;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.model.LatLng;
public class MainActivity extends AppCompatActivity
//Globals
public String uname = null;
//private MyLocationReceiver myLocationReceiver;
public double lat = 0;
public double lng = 0;
public LatLng curr_pos;
public final String NULL_STRING = "NULL";
//Get GUI handles
public Button sendButton; //
public EditText username;
public Button MapButton; //
public EditText LatBox;
public EditText LngBox;
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data)
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == 1)
if(resultCode == RESULT_OK)
String LatText = data.getStringExtra("LatValue");
String LngText = data.getStringExtra("LngValue");
LatBox.setText(LatText); // <- GETTING NULLPOINTER HERE
LngBox.setText(LngText); // <- GETTING NULLPOINTER HERE
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
//set GUI for MainActivity
setContentView(R.layout.activity_main);
//EventBus.getDefault().register(this);
//Log.d("Register", "EventBus registered in onCreate");
MapButton = (Button) findViewById(R.id.locationButton);
//Call the class which will handle finding coordinates
MapButton.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
Intent MapIntent = new Intent(getApplicationContext(), ActivityMap.class);
startActivityForResult(MapIntent, 1);
);
sendButton = (Button) findViewById(R.id.Submit);
//Set action for Button
sendButton.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
//Get username from user
username = (EditText) findViewById(R.id.UsernameText);
uname = username.getText().toString();
//Generate intent to start IntentService
Intent i = new Intent(getApplicationContext(), Register.class);
//Put the extra field of username
i.putExtra("username", uname);
i.putExtra("latitude", lat);
i.putExtra("longitude", lng);
i.putExtra("type", "meetup.be2015.gcm_meetup.MAIN_ACTIVITY");
//Start the IntentService on a different thread
startService(i);
);
活动地图
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.os.Bundle;
import android.os.Looper;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import java.util.logging.Handler;
public class ActivityMap extends AppCompatActivity implements
GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener, com.google.android.gms.location.LocationListener
protected GoogleApiClient mGoogleApiClient;
LocationRequest mLocationRequest;
protected Location mLastLocation;
public LocationListener listener;
protected final String TAG = getClass().getSimpleName();
public EditText t1;
public EditText t2;
public Button b1;
public final String NULL = "NULL";
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_activity_map);
t1 = (EditText)findViewById(R.id.editText1);
t2 = (EditText)findViewById(R.id.editText2);
b1 = (Button)findViewById(R.id.BackButton);
buildGoogleApiClient();
mGoogleApiClient.connect();
b1.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
Intent i = new Intent(getApplicationContext(), MainActivity.class);
if (mLastLocation != null)
i.putExtra("LatValue",String.valueOf(mLastLocation.getLatitude()));
i.putExtra("LngValue",String.valueOf(mLastLocation.getLongitude()));
setResult(RESULT_OK, i);
finish();
else
i.putExtra("LatValue","NULL");
i.putExtra("LngValue","NULL");
setResult(RESULT_OK, i);
finish();
);
@Override
protected void onStart()
super.onStart();
mGoogleApiClient.connect();
@Override
protected void onStop()
super.onStop();
if (mGoogleApiClient.isConnected())
mGoogleApiClient.disconnect();
protected synchronized void buildGoogleApiClient()
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
Log.d(TAG,"Built Client successfully...");
@Override
public void onConnectionFailed(ConnectionResult connectionResult)
Log.d(TAG,"ConnectionFailed() with code "+connectionResult.getErrorCode());
@Override
public void onConnected(Bundle bundle)
Log.d(TAG, "In onConnected..");
mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
if(mLastLocation == null)
mLocationRequest = new LocationRequest();
mLocationRequest.setInterval(1000);
mLocationRequest.setFastestInterval(1000);
mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
else
t1.setText(String.valueOf(mLastLocation.getLatitude()));
t2.setText(String.valueOf(mLastLocation.getLongitude()));
//LatLng lng = new LatLng(mLastLocation.getLatitude(), mLastLocation.getLongitude());
Toast.makeText(this, "Retrieved location from FusedLocation", Toast.LENGTH_LONG).show();
Intent intent = new Intent();
intent.putExtra("LatValue",String.valueOf(mLastLocation.getLatitude()));
intent.putExtra("LngValue", String.valueOf(mLastLocation.getLongitude()));
setResult(RESULT_OK, intent);
finish();
@Override
public void onConnectionSuspended(int i)
Log.d(TAG,"ConnectionSuspended() with code "+i);
@Override
public void onLocationChanged(Location location)
mLastLocation = location;
double latitude = mLastLocation.getLatitude();
double longitude = mLastLocation.getLongitude();
if(latitude != 0 && longitude != 0)
t1.setText(String.valueOf(latitude));
t2.setText(String.valueOf(longitude));
Toast.makeText(this, "Retrieved Location from onLocationChanged...", Toast.LENGTH_LONG).show();
Intent intent = new Intent();
intent.putExtra("LatValue",String.valueOf(mLastLocation.getLatitude()));
intent.putExtra("LngValue", String.valueOf(mLastLocation.getLongitude()));
setResult(RESULT_OK, intent);
finish();
else
t1.setText(NULL);
t2.setText(NULL);
Toast.makeText(this, "Problem with location...", Toast.LENGTH_LONG).show();
Intent intent = new Intent();
intent.putExtra("LatValue", "NULL");
intent.putExtra("LngValue", "NULL");
setResult(RESULT_OK, intent);
finish();
编辑：这是我的 LogCat
03-13 13:06:59.940 14638-14638/meetup.be2015.gcm_meetup E/AndroidRuntime: 致命异常: main java.lang.RuntimeException：传递结果失败 ResultInfowho=null, request=1, result=-1, data=Intent (有附加功能) 到活动 meetup.be2015.gcm_meetup/meetup.be2015.gcm_meetup.MainActivity： java.lang.NullPointerException 在 android.app.ActivityThread.deliverResults(ActivityThread.java:3216) 在 android.app.ActivityThread.handleSendResult(ActivityThread.java:3259) 在 android.app.ActivityThread.access$1200(ActivityThread.java:140) 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1285) 在 android.os.Handler.dispatchMessage(Handler.java:99) 在 android.os.Looper.loop(Looper.java:174) 在 android.app.ActivityThread.main(ActivityThread.java:4952) 在 java.lang.reflect.Method.invokeNative(Native Method) 在 java.lang.reflect.Method.invoke(Method.java:511) 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794) 在 dalvik.system.NativeStart.main（本机方法） 引起：java.lang.NullPointerException 在 meetup.be2015.gcm_meetup.MainActivity.onActivityResult(MainActivity.java:60) 在 android.app.Activity.dispatchActivityResult(Activity.java:5372) 在 android.app.ActivityThread.deliverResults(ActivityThread.java:3212) 在 android.app.ActivityThread.handleSendResult(ActivityThread.java:3259) 在 android.app.ActivityThread.access$1200(ActivityThread.java:140) 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1285) 在 android.os.Handler.dispatchMessage(Handler.java:99) 在 android.os.Looper.loop(Looper.java:174) 在 android.app.ActivityThread.main(ActivityThread.java:4952) 在 java.lang.reflect.Method.invokeNative(Native Method) 在 java.lang.reflect.Method.invoke(Method.java:511) 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794) 在 dalvik.system.NativeStart.main(Native Method)
【问题讨论】：
使用断点调试您的代码并找出错误所在。第二个活动返回的数据没有错误。 【参考方案1】：你必须初始化 LatBox
LatBox = (EditText) findViewById(R.id.xxx);
【讨论】：
天啊！天哪，我怎么会错过呢？谢谢，伙计！ 是的！完毕！谢了哥们！轻信率最高，嗯？以上是关于尝试将数据从子活动返回到 MainActivity 时获取 NullPointerException的主要内容，如果未能解决你的问题，请参考以下文章
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