通过构造函数传递ArrayAdapter | 列表视图

huangapple
go评论120阅读模式
英文:

Passing Array Adapter via Constructor | ListView

问题

我试图将来自LocationsFragment.class的适配器用于我的DeviceAdmin.class，以将两个字符串mylatitude和mylongitude添加到我的ListView中。
我正在使用构造函数方法。
但是每当我在我的DeviceAdmin.class中调用adapter.add(mylatitude + " " + mylongitude);时，它似乎返回null。

  1.         at com.ayush.trixter.ui.captures.DeviceAdmin$1.onLocationChanged(DeviceAdmin.java:103)

第103行是：adapter.add("Latitude: " + mylat + "Longitude: " + mylon);

DeviceAdmin.class

  1. package com.ayush.trixter.ui.captures;
  3. import android.Manifest;
  4. import android.annotation.SuppressLint;
  5. import android.app.admin.DeviceAdminReceiver;
  6. import android.app.admin.DevicePolicyManager;
  7. import android.content.Context;
  8. import android.content.Intent;
  9. import android.content.pm.PackageManager;
  10. import android.graphics.Paint;
  11. import android.graphics.SurfaceTexture;
  12. import android.hardware.Camera;
  13. import android.hardware.camera2.CameraAccessException;
  14. import android.hardware.camera2.CameraCaptureSession;
  15. import android.hardware.camera2.CameraCharacteristics;
  16. import android.hardware.camera2.CameraManager;
  17. import android.location.Criteria;
  18. import android.location.Location;
  19. import android.location.LocationListener;
  20. import android.location.LocationManager;
  21. import android.os.Build;
  22. import android.os.Looper;
  23. import android.os.UserHandle;
  24. import android.util.Log;
  25. import android.util.SparseIntArray;
  26. import android.view.ContextThemeWrapper;
  27. import android.view.Surface;
  28. import android.view.View;
  29. import android.widget.Adapter;
  30. import android.widget.ArrayAdapter;
  31. import android.widget.ListView;
  32. import android.widget.Toast;
  34. import androidx.annotation.NonNull;
  35. import androidx.core.content.PermissionChecker;
  37. import com.ayush.trixter.R;
  38. import com.ayush.trixter.ui.locations.LocationFragment;
  39. import com.google.android.gms.location.LocationCallback;
  40. import com.google.android.gms.location.LocationRequest;
  41. import com.google.android.gms.location.LocationServices;
  42. import com.google.android.material.snackbar.Snackbar;
  43. import com.google.firebase.database.FirebaseDatabase;
  45. import java.util.ArrayList;
  47. public class DeviceAdmin extends DeviceAdminReceiver
  48. {
  49.     private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
  50.     public CameraManager cam;
  51.     LocationManager locationManager;
  52.     final String TAG = "[Trixter]";
  53.     DevicePolicyManager mgr;
  54.     FirebaseDatabase db;
  55.     public boolean mTracking = false;
  56.     public ArrayList<String> listItems=new ArrayList<>();
  57.     LocationFragment lf = new LocationFragment();
  58.     ArrayAdapter<String> adapter = lf.adapter;
  62.     @Override
  63.     public void onPasswordFailed(@NonNull Context ctx, @NonNull Intent intent, @NonNull UserHandle user) {
  64.         super.onPasswordFailed(ctx, intent, user);
  65.         cam = (CameraManager) ctx.getSystemService(Context.CAMERA_SERVICE);
  66.         mgr = (DevicePolicyManager) ctx.getSystemService(Context.DEVICE_POLICY_SERVICE);
  68.         Log.d(TAG,"PasswordFailed");
  69.         int pwdfailcount = mgr.getCurrentFailedPasswordAttempts();
  71.         if(pwdfailcount==3)
  72.         {
  73.             takeSnapShots();
  74.             getloc(ctx);
  76.         }
  77.     }
  79.     public void getloc(Context ctx)
  80.     {
  81.         locationManager = (LocationManager) ctx.getSystemService(Context.LOCATION_SERVICE);
  82.         Criteria criteria = new Criteria();
  83.         String provider =  locationManager.getBestProvider(criteria,true);
  84.         boolean gps_enabled = false;
  85.         boolean network_enabled = false;
  87.         try
  88.         { gps_enabled =   locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER); }
  89.         catch (Exception e) {}
  90.         try { network_enabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);} catch (Exception e) {}
  92.         if(PermissionChecker.checkSelfPermission(ctx, Manifest.permission.ACCESS_COARSE_LOCATION) == PermissionChecker.PERMISSION_GRANTED &&
  93.                 PermissionChecker.checkSelfPermission(ctx,Manifest.permission.ACCESS_FINE_LOCATION) == PermissionChecker.PERMISSION_GRANTED) {
  94.             if(gps_enabled == true && network_enabled ==true) {
  95.                 locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, new LocationListener() {
  96.                     @Override
  97.                     public void onLocationChanged(@NonNull Location loc) {
  98.                         double mylat = loc.getLatitude();
  99.                         double mylon = loc.getLongitude();
  100.                         double myacc = loc.getAccuracy();
  101.                         double time = loc.getTime();
  102.                         double myalt = loc.getAltitude();
  103.                         Log.d("[TrixterLocation]", "The Latitude:- " + mylat + "\nThe Longitude:- " + mylon +
  104.                                 "\nThe Altitude:- " + myalt + "\n The Accuracy" + myacc + "\nThe Time:- " + time);
  105.                         adapter.add("Latitude: " + mylat + "Longitude: " + mylon);
  106.                     }
  107.                 });
  108.             }
  109.             else
  110.             {
  111.                 Toast.makeText(ctx, "Location is not enabled", Toast.LENGTH_SHORT).show();
  112.                 Log.d("[Trixter] ","Error: Location or Internet Not Enabled");
  113.             }
  114.         }
  116.     }
  120.     private void takeSnapShots()
  121.     {
  123.     }
  125. }

LocationsFragment.class

  1. package com.ayush.trixter.ui.locations;
  3. import android.content.Context;
  4. import android.location.LocationManager;
  5. import android.os.Bundle;
  6. import android.view.LayoutInflater;
  7. import android.view.View;
  8. import android.view.ViewGroup;
  9. import android.widget.AdapterView;
  10. import android.widget.ArrayAdapter;
  11. import android.widget.ListView;
  12. import android.widget.TextView;
  13. import android.widget.Toast;
  15. import androidx.annotation.NonNull;
  16. import androidx.annotation.Nullable;
  17. import androidx.fragment.app.Fragment;
  18. import androidx.fragment.app.ListFragment;
  19. import androidx.lifecycle.Observer;
  20. import androidx.lifecycle.ViewModelProviders;
  22. import com.ayush.trixter.R;
  23. import com.ayush.trixter.ui.captures.DeviceAdmin;
  25. import java.util.ArrayList;
  27. public class LocationFragment extends ListFragment {
  29.     ListView loclst;
  30.     LocationManager locationManager;
  31.     public ArrayList<String> listItems=new ArrayList<>();
  32.     public ArrayAdapter<String> adapter = (ArrayAdapter<String>) getListAdapter();
  34.     public LocationFragment()
  35.     {
  37.     }
  38.     public View onCreateView(@NonNull LayoutInflater inflater,
  39.                              ViewGroup container, Bundle savedInstanceState) {
  40.         View root = inflater.inflate(R.layout.fragment_locations, container, false);
  41.             loclst = root.findViewById(android.R.id.list);
  42.             Context context = getActivity();
  43.             locationManager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
  44.             adapter = new ArrayAdapter<String>(getActivity(),   android.R.layout.simple_list_item_2 , listItems);
  45.             loclst.setAdapter(adapter);
  47.           return root;
  48.     }
  50. }

根据我的观察：
它会返回null，因为ArrayAdapter未初始化，并且只有在Fragment打开时才会初始化，即在onCreateView()方法中。

但是我无法找到使其工作的解决方案。
如果有人有更好的方法来更轻松地完成这个任务，请告诉我。

英文:

I am trying to use adapter from my LocationsFragment.class into my DeviceAdmin.class to add two Strings say mylatitude and mylongitude to my ListView.
I am going through Constructor Method.
But it seems to return null, whenever I call adapter.add(mylatitude + &quot; &quot; + mylongitude); in my DeviceAdmin.class

  1.   java.lang.NullPointerException: Attempt to invoke virtual method &#39;void android.widget.ArrayAdapter.add(java.lang.Object)&#39; on a null object reference
  2. at com.ayush.trixter.ui.captures.DeviceAdmin$1.onLocationChanged(DeviceAdmin.java:103)

Line 103 is : adapter.add(&quot;Latitude: &quot; + mylat + &quot;Longitude: &quot; + mylon);

DeviceAdmin.class

  2. import android.Manifest;
  3. import android.annotation.SuppressLint;
  4. import android.app.admin.DeviceAdminReceiver;
  5. import android.app.admin.DevicePolicyManager;
  6. import android.content.Context;
  7. import android.content.Intent;
  8. import android.content.pm.PackageManager;
  9. import android.graphics.Paint;
  10. import android.graphics.SurfaceTexture;
  11. import android.hardware.Camera;
  12. import android.hardware.camera2.CameraAccessException;
  13. import android.hardware.camera2.CameraCaptureSession;
  14. import android.hardware.camera2.CameraCharacteristics;
  15. import android.hardware.camera2.CameraManager;
  16. import android.location.Criteria;
  17. import android.location.Location;
  18. import android.location.LocationListener;
  19. import android.location.LocationManager;
  20. import android.os.Build;
  21. import android.os.Looper;
  22. import android.os.UserHandle;
  23. import android.util.Log;
  24. import android.util.SparseIntArray;
  25. import android.view.ContextThemeWrapper;
  26. import android.view.Surface;
  27. import android.view.View;
  28. import android.widget.Adapter;
  29. import android.widget.ArrayAdapter;
  30. import android.widget.ListView;
  31. import android.widget.Toast;
  32. import androidx.annotation.NonNull;
  33. import androidx.core.content.PermissionChecker;
  34. import com.ayush.trixter.R;
  35. import com.ayush.trixter.ui.locations.LocationFragment;
  36. import com.google.android.gms.location.LocationCallback;
  37. import com.google.android.gms.location.LocationRequest;
  38. import com.google.android.gms.location.LocationServices;
  39. import com.google.android.material.snackbar.Snackbar;
  40. import com.google.firebase.database.FirebaseDatabase;
  41. import java.util.ArrayList;
  42. public class DeviceAdmin extends DeviceAdminReceiver
  43. {
  44. private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
  45. public CameraManager cam;
  46. LocationManager locationManager;
  47. final String TAG = &quot;[Trixter]&quot;;
  48. DevicePolicyManager mgr;
  49. FirebaseDatabase db;
  50. public boolean mTracking = false;
  51. public ArrayList&lt;String&gt; listItems=new ArrayList&lt;&gt;();
  52. LocationFragment lf = new LocationFragment();
  53. ArrayAdapter&lt;String&gt; adapter = lf.adapter;
  54. @Override
  55. public void onPasswordFailed(@NonNull Context ctx, @NonNull Intent intent, @NonNull UserHandle user) {
  56. super.onPasswordFailed(ctx, intent, user);
  57. cam = (CameraManager) ctx.getSystemService(Context.CAMERA_SERVICE);
  58. mgr = (DevicePolicyManager) ctx.getSystemService(Context.DEVICE_POLICY_SERVICE);
  59. Log.d(TAG,&quot;PasswordFailed&quot;);
  60. int pwdfailcount = mgr.getCurrentFailedPasswordAttempts();
  61. if(pwdfailcount==3)
  62. {
  63. takeSnapShots();
  64. getloc(ctx);
  65. }
  66. }
  67. public void getloc(Context ctx)
  68. {
  69. locationManager = (LocationManager) ctx.getSystemService(Context.LOCATION_SERVICE);
  70. Criteria criteria = new Criteria();
  71. String provider =  locationManager.getBestProvider(criteria,true);
  72. boolean gps_enabled = false;
  73. boolean network_enabled = false;
  74. try
  75. { gps_enabled =   locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER); }
  76. catch (Exception e) {}
  77. try { network_enabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);} catch (Exception e) {}
  78. if(PermissionChecker.checkSelfPermission(ctx, Manifest.permission.ACCESS_COARSE_LOCATION) == PermissionChecker.PERMISSION_GRANTED &amp;&amp; PermissionChecker.checkSelfPermission(ctx,Manifest.permission.ACCESS_FINE_LOCATION) == PermissionChecker.PERMISSION_GRANTED) {
  79. if(gps_enabled == true &amp;&amp; network_enabled ==true) {
  80. locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, new LocationListener() {
  81. @Override
  82. public void onLocationChanged(@NonNull Location loc) {
  83. double mylat = loc.getLatitude();
  84. double mylon = loc.getLongitude();
  85. double myacc = loc.getAccuracy();
  86. double time = loc.getTime();
  87. double myalt = loc.getAltitude();
  88. Log.d(&quot;[TrixterLocation]&quot;, &quot;The Latitude:- &quot; + mylat + &quot;\nThe Longitude:- &quot; + mylon + &quot;\nThe Altitude:- &quot; + myalt + &quot;\n The Accuracy&quot; + myacc + &quot;\nThe Time:- &quot; + time);
  89. adapter.add(&quot;Latitude: &quot; + mylat + &quot;Longitude: &quot; + mylon);
  90. }
  91. });
  92. }
  93. else
  94. {
  95. Toast.makeText(ctx, &quot;Location is not enabled&quot;, Toast.LENGTH_SHORT).show();
  96. Log.d(&quot;[Trixter] &quot;,&quot;Error: Location or Internet Not Enabled&quot;);
  97. }
  98. }
  99. }
  100. private void takeSnapShots()
  101. {
  102. }
  103. }

LocationsFragment.class

  1. package com.ayush.trixter.ui.locations;
  2. import android.content.Context;
  3. import android.location.LocationManager;
  4. import android.os.Bundle;
  5. import android.view.LayoutInflater;
  6. import android.view.View;
  7. import android.view.ViewGroup;
  8. import android.widget.AdapterView;
  9. import android.widget.ArrayAdapter;
  10. import android.widget.ListView;
  11. import android.widget.TextView;
  12. import android.widget.Toast;
  13. import androidx.annotation.NonNull;
  14. import androidx.annotation.Nullable;
  15. import androidx.fragment.app.Fragment;
  16. import androidx.fragment.app.ListFragment;
  17. import androidx.lifecycle.Observer;
  18. import androidx.lifecycle.ViewModelProviders;
  19. import com.ayush.trixter.R;
  20. import com.ayush.trixter.ui.captures.DeviceAdmin;
  21. import java.util.ArrayList;
  22. public class LocationFragment extends ListFragment {
  23. ListView loclst;
  24. LocationManager locationManager;
  25. public ArrayList&lt;String&gt; listItems=new ArrayList&lt;&gt;();
  26. public ArrayAdapter&lt;String&gt; adapter = (ArrayAdapter&lt;String&gt;) getListAdapter();
  27. public LocationFragment()
  28. {
  29. }
  30. public View onCreateView(@NonNull LayoutInflater inflater,
  31. ViewGroup container, Bundle savedInstanceState) {
  32. View root = inflater.inflate(R.layout.fragment_locations, container, false);
  33. loclst = root.findViewById(android.R.id.list);
  34. Context context = getActivity();
  35. locationManager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
  36. adapter = new ArrayAdapter&lt;String&gt;(getActivity(),   android.R.layout.simple_list_item_2 , listItems);
  37. loclst.setAdapter(adapter);
  38. return root;
  39. }
  40. }

According to me:-
It would return null since ArrayAdapter is not initialized and only gets initialized when the Fragment Opens i.e. onCreateView()

But I am not able to find a solution to make it work.
Also if anyone has a better idea to do this more easily please tell.

答案1

得分: 1

这不会起作用，因为你在你的DeviceAdmin类上创建了一个新的LocationFragment。

你需要做的是访问实际的LocationFragment。

要正确回答你，我需要知道：

  1. 片段是从哪里创建的？
  2. 你在哪里调用getLoc方法？
英文:

It wont work because you're creating a new LocationFramgent on your DeviceAdmin class.

What you need to do is access the actual LocationFragment.

To answer you properly i need to knwo:

Where is the fragment being created from?

And where do you call getLoc method?

huangapple
  • 本文由 发表于 2020年8月13日 19:13:27
  • 转载请务必保留本文链接：https://go.coder-hub.com/63393924.html
  • android
  • android-fragments
  • android-studio
  • java
  • listview
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