我想创建一个应用程序，使用Locaion manager获取坐标中的用户位置信息。问题是我的应用程序在运行时总是停止并且总是得到java.lang.NullPointerException
这是我的主要活动
package com.ionlab.project.volley;
import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.app.ProgressDialog;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.provider.MediaStore;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.util.Base64;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.ionlab.project.volley.app.AppController;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.HashMap;
import java.util.Map;
public class MainActivity extends AppCompatActivity implements LocationListener {
//location
private TextView textView;
private LocationManager locationManager;
//waktu
TextView textviewDate;
Button buttonChoose;
FloatingActionButton buttonUpload;
Toolbar toolbar;
ImageView imageView;
EditText txt_name;
EditText txt_item;
Bitmap bitmap, decoded;
int success;
int PICK_IMAGE_REQUEST = 1;
int bitmap_size = 60; // range 1 - 100
private static final String TAG = MainActivity.class.getSimpleName();
/* 10.0.2.2 adalah IP Address localhost Emulator Android Studio. Ganti IP Address tersebut dengan
IP Address Laptop jika di RUN di HP/Genymotion. HP/Genymotion dan Laptop harus 1 jaringan! */
private String UPLOAD_URL = "http://192.168.1.4/android/upload_image/upload.php";
private static final String TAG_SUCCESS = "success";
private static final String TAG_MESSAGE = "message";
private String KEY_IMAGE = "image";
private String KEY_NAME = "name";
private String KEY_ITEM = "item";
private String KEY_LOKASI = "lokasi";
private String KEY_WAKTU = "waktu";
String tag_json_obj = "json_obj_req";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonChoose = (Button) findViewById(R.id.buttonChoose);
buttonUpload = (FloatingActionButton) findViewById(R.id.buttonUpload);
txt_name = (EditText) findViewById(R.id.editText);
txt_item = (EditText) findViewById(R.id.editItem);
imageView = (ImageView) findViewById(R.id.imageView);
buttonChoose.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showFileChooser();
}
});
buttonUpload.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
uploadImage();
}
});
//Calendar
Calendar calendar = Calendar.getInstance();
String currenDate = DateFormat.getDateInstance(DateFormat.FULL).format(calendar.getTime());
textviewDate = findViewById(R.id.text_view_date);
textviewDate.setText(currenDate);
//textloc
textView = (TextView) findViewById(R.id.id_textview);
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
Location location = locationManager.getLastKnownLocation(locationManager.NETWORK_PROVIDER);
onLocationChanged(location);
}
public String getStringImage(Bitmap bmp) {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bmp.compress(Bitmap.CompressFormat.JPEG, bitmap_size, baos);
byte[] imageBytes = baos.toByteArray();
String encodedImage = Base64.encodeToString(imageBytes, Base64.DEFAULT);
return encodedImage;
}
private void uploadImage() {
//menampilkan progress dialog
final ProgressDialog loading = ProgressDialog.show(this, "Uploading...", "Please wait...", false, false);
StringRequest stringRequest = new StringRequest(Request.Method.POST, UPLOAD_URL,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.e(TAG, "Response: " + response.toString());
try {
JSONObject jObj = new JSONObject(response);
success = jObj.getInt(TAG_SUCCESS);
if (success == 1) {
Log.e("v Add", jObj.toString());
Toast.makeText(MainActivity.this, jObj.getString(TAG_MESSAGE), Toast.LENGTH_LONG).show();
kosong();
} else {
Toast.makeText(MainActivity.this, jObj.getString(TAG_MESSAGE), Toast.LENGTH_LONG).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
//menghilangkan progress dialog
loading.dismiss();
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
//menghilangkan progress dialog
loading.dismiss();
//menampilkan toast
Toast.makeText(MainActivity.this, error.getMessage().toString(), Toast.LENGTH_LONG).show();
Log.e(TAG, error.getMessage().toString());
}
}) {
@Override
protected Map<String, String> getParams() {
//membuat parameters
Map<String, String> params = new HashMap<String, String>();
//menambah parameter yang di kirim ke web servis
params.put(KEY_IMAGE, getStringImage(decoded));
params.put(KEY_NAME, txt_name.getText().toString().trim());
params.put(KEY_ITEM, txt_item.getText().toString().trim());
params.put(KEY_WAKTU, textviewDate.getText().toString().trim());
params.put(KEY_LOKASI, textView.getText().toString().trim());
//kembali ke parameters
Log.e(TAG, "" + params);
return params;
}
};
AppController.getInstance().addToRequestQueue(stringRequest, tag_json_obj);
}
private void showFileChooser() {
Intent intent = new Intent();
intent.setType("image/*");
intent.setAction(Intent.ACTION_GET_CONTENT);
startActivityForResult(Intent.createChooser(intent, "Select Picture"), PICK_IMAGE_REQUEST);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == PICK_IMAGE_REQUEST && resultCode == RESULT_OK && data != null && data.getData() != null) {
Uri filePath = data.getData();
try {
//mengambil fambar dari Gallery
bitmap = MediaStore.Images.Media.getBitmap(getContentResolver(), filePath);
// 512 adalah resolusi tertinggi setelah image di resize, bisa di ganti.
setToImageView(getResizedBitmap(bitmap, 512));
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void kosong() {
imageView.setImageResource(0);
txt_name.setText(null);
txt_item.setText(null);
}
private void setToImageView(Bitmap bmp) {
//compress image
ByteArrayOutputStream bytes = new ByteArrayOutputStream();
bmp.compress(Bitmap.CompressFormat.JPEG, bitmap_size, bytes);
decoded = BitmapFactory.decodeStream(new ByteArrayInputStream(bytes.toByteArray()));
//menampilkan gambar yang dipilih dari camera/gallery ke ImageView
imageView.setImageBitmap(decoded);
}
// fungsi resize image
public Bitmap getResizedBitmap(Bitmap image, int maxSize) {
int width = image.getWidth();
int height = image.getHeight();
float bitmapRatio = (float) width / (float) height;
if (bitmapRatio > 1) {
width = maxSize;
height = (int) (width / bitmapRatio);
} else {
height = maxSize;
width = (int) (height * bitmapRatio);
}
return Bitmap.createScaledBitmap(image, width, height, true);
}
@Override
public void onLocationChanged(Location location) {
double longitude = location.getLongitude();
double latitude = location.getLatitude();
textView.setText("Longitude:" + longitude + "\n" + "Latitude:" + latitude);
}
@Override
public void onStatusChanged(String s, int i, Bundle bundle) {
}
@Override
public void onProviderEnabled(String s) {
}
@Override
public void onProviderDisabled(String s) {
}
}
我还确保我的Android清单正确
我花了很多时间试图解决这个问题，浏览了很多关于这个主题的网页，尝试了我自己的不同代码。 它仍然会发生。我是Android的初学者。拜托，请帮助我。有没有办法解决我的问题？
这是我的logcat LogCat
答案 0 :(得分：1)
首先，您应该将logcat以文本形式包含在您的问题中！
但是，从我从屏幕截图中可以看到的问题是onLocationChanged()方法。检查＆＃34; location＆＃34;在尝试阅读之前查看它是否为null。
@Override
public void onLocationChanged(Location location) {
if(location != null){
double longitude = location.getLongitude();
double latitude = location.getLatitude();
textView.setText("Longitude:" + longitude + "\n" + "Latitude:" + latitude);
}
else{
Log.e(TAG, "onLocationChanged -- location is null!");
}
}
注意：
万一你不知道＆＃34; TAG＆＃34;通常会添加到大多数Android类的开头，如下所示：
public class MainActivity extends AppCompatActivity implements LocationListener {
private static final String TAG = MainActivity.class.getSimpleName();
为什么MainActivity.class.getSimpleName()而不仅仅是＆＃34; MainActivity＆＃34;？因为如果您重构代码，那么名称将自动更改。
修改
您是否在清单文件中添加了必要的权限？
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-feature android:name="android.hardware.location.gps"/>