我是android和mySQL服务器的新手。我正在编写一个应该从服务器检索JSON数据的应用程序，然后将数据存储到对象“Court”。我正在使用Volley库。但是当我尝试存储它并在“onRespons”方法之外使用它时，我得到的对象或String为null。
这是我到目前为止所尝试的内容。
DatabaseConnection.java UPDATED !!!
public class DataBaseConnection extends AppCompatActivity {
String temp;
Court court;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
court = new Court();
}
public String retrive(final Context context, final String newURL) {
final RequestQueue request;
request = newRequestQueue(context);
Response.Listener<String> sendR = new Response.Listener<String>() {
//Court[] courts;
@Override
public void onResponse(String response) {
sharedResponse(response);
court.setName(response);
}
};
System.out.println(court.getName());
Response.ErrorListener errorr = new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
System.out.println("There is an error");
System.out.println(error.getMessage());
}
};
StringRequest sender = new StringRequest(Request.Method.POST, newURL,sendR,errorr) {
@Override
protected Map<String, String> getParams() throws AuthFailureError {
Map<String, String> parameters = new HashMap<String, String>();
parameters.put("test", "test");
return parameters;
}
};
request.add(sender);
return court.getName();
}
private void sharedResponse(String response) {
SharedPreferences m = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = m.edit();
editor.putString("Response", response);
editor.commit();
}
}
这就是升级班：
public class Listing extends AppCompatActivity {
private String url = "http://192.168.1.106/list/list.php";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_listing);
String JSON="";
DataBaseConnection connect = new DataBaseConnection();
JSON = connect.retrive(getApplicationContext(), url);
System.out.println("first time"+JSON);
SharedPreferences m = PreferenceManager.getDefaultSharedPreferences(this);
JSON = m.getString("Response", "");
System.out.println("Second time"+JSON);
}
}
如您所见，我尝试使用简单的返回值和SharedPrefrences，我也尝试使用Intent。但他们都没有和我合作。从Log Cat开始，显示有关NULLPointerException的一些错误。
LogCat：
12-05 11:45:40.815 30821-30821/com.saihatandroid.owen.lising I/System.out: first time
12-05 11:45:40.817 30821-30821/com.saihatandroid.owen.lising I/System.out: Second time
12-05 11:45:40.865 30821-30852/com.saihatandroid.owen.lising I/Adreno: QUALCOMM build : 4d8478c, I7b6ba47bd6
Build Date : 02/09/16
OpenGL ES Shader Compiler Version: XE031.07.00.01
Local Branch : mybranch18178856
Remote Branch : quic/LA.HB.1.3.1_rb1.11
Remote Branch : NONE
Reconstruct Branch : NOTHING
12-05 11:45:41.025 30821-30821/com.saihatandroid.owen.lising E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.saihatandroid.owen.lising, PID: 30821
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ContextWrapper.getPackageName(ContextWrapper.java:133)
at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:375)
at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:370)
at com.saihatandroid.owen.lising.DataBaseConnection.sharedResponse(DataBaseConnection.java:148)
at com.saihatandroid.owen.lising.DataBaseConnection.access$000(DataBaseConnection.java:44)
at com.saihatandroid.owen.lising.DataBaseConnection$1.onResponse(DataBaseConnection.java:75)
at com.saihatandroid.owen.lising.DataBaseConnection$1.onResponse(DataBaseConnection.java:61)
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:60)
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:30)
at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:168)
at android.app.ActivityThread.main(ActivityThread.java:5885)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:819)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:709)
同样发现此错误在Logcat的底部
D/Process: com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException:113 java.lang.ThreadGroup.uncaughtException:693 java.lang.ThreadGroup.uncaughtException:690
我需要你的帮助我在网络上找不到任何与之相关的内容，我尝试了所有选项。 谢谢