Passing in context to a Java Class - Android

Question

When I open this activity in my app (Template1Activity) the app crashes with the following message:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference

My code for Template1Activity is:

package com.idleappsinc.smartmirror;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;

/**
 * Created by Luke on 04/02/2018.
 */

public class Template1Activity extends AppCompatActivity {

    Preferences sharedPreferences;
    TimeModule timeModule = new TimeModule();

    TextView timeDisplayTextView;
    TextView timeLocationTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_template_1);
        sharedPreferences = new Preferences(this);

        timeDisplayTextView = findViewById(R.id.time_display_text_view);
        timeLocationTextView = findViewById(R.id.time_location_text_view);

        timeModule.startTimer(timeDisplayTextView);
        timeLocationTextView.setText(timeModule.getCurrentLocation());


        View decorView = getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_FULLSCREEN;
        decorView.setSystemUiVisibility(uiOptions);

    }

}

My code for TimeModule is:

package com.idleappsinc.smartmirror;


import android.app.Activity;
import android.content.Context;
import android.location.Address;
import android.location.Geocoder;
import android.location.Location;
import android.location.LocationManager;
import android.os.Handler;
import android.widget.TextView;

import java.io.IOException;
import java.util.Calendar;
import java.util.List;
import java.util.Locale;

/**
 * Created by Luke on 05/02/2018.
 */

public class TimeModule extends Activity {

    Preferences sharedPreferences = new Preferences(this);
    List<Address> addressList;

    @SuppressWarnings({"MissingPermission"})
    public String getCurrentLocation() {
        String currentLocation = "";

        Geocoder geocoder = new Geocoder(this, Locale.getDefault());
        try {
            LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
            Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
            addressList = geocoder.getFromLocation(location.getLatitude(), location.getLongitude(), 1);
            String area = addressList.get(0).getLocality();
            String country = addressList.get(0).getCountryCode();

            currentLocation = area + ", " + country;

        } catch (IOException e) {
            e.printStackTrace();
        }

        return currentLocation;
    }

    public void startTimer(final TextView timeDisplayTextView) {

        final Handler handler = new Handler();
        Runnable runnable = new Runnable() {

            @Override
            public void run() {
                try {

                    if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_clock_hours))) {
                        // User wants 24 hour format

                        if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_segment_seconds))) {
                            // User wants to see seconds
                            int secondsLength = String.valueOf(Calendar.getInstance().get(Calendar.SECOND)).length();
                            int minutesLength = String.valueOf(Calendar.getInstance().get(Calendar.MINUTE)).length();

                            if (secondsLength == 1) {
                                if (minutesLength == 1) {
                                    // Seconds = 0-9
                                    // Minutes = 0-9
                                    timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND));
                                } else {
                                    // Seconds = 0-9
                                    timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND));
                                }
                            } else {
                                if (minutesLength == 1) {
                                    // Minutes = 0-9
                                    timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND));
                                } else {
                                    // Seconds = 0-9
                                    timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND));
                                }
                                timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND));
                            }

                        } else {
                            timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE));
                        }


                    } else {
                        // The user wants the 12 hours format

                        if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_segment_seconds))) {
                            int secondsLength = String.valueOf(Calendar.getInstance().get(Calendar.SECOND)).length();
                            int minutesLength = String.valueOf(Calendar.getInstance().get(Calendar.MINUTE)).length();

                            if (secondsLength == 1) {
                                Calendar cal = Calendar.getInstance();
                                if (cal.get(Calendar.AM_PM) == Calendar.PM) {
                                    if (minutesLength == 1) {
                                        // Seconds = 0-9
                                        // Minutes = 0-9
                                        // PM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
                                    } else {
                                        // Seconds = 0-9
                                        // PM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
                                    }
                                } else {
                                    if (minutesLength == 1) {
                                        // Seconds = 0-9
                                        // Minutes = 0-9
                                        // AM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "am");
                                    } else {
                                        // Seconds = 0-9
                                        // Minutes = 0-9
                                        // AM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "am");
                                    }
                                }

                            } else {
                                Calendar cal = Calendar.getInstance();
                                if (cal.get(Calendar.AM_PM) == Calendar.PM) {
                                    if (minutesLength == 1) {
                                        // Minutes = 0-9
                                        // PM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
                                    } else {
                                        // PM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
                                    }
                                } else {
                                    if (minutesLength == 1) {
                                        // Minutes = 0-9
                                        // AM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "am");
                                    } else {
                                        // AM
                                        timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "am");
                                    }
                                }
                            }
                        } else {
                            Calendar cal = Calendar.getInstance();
                            if (cal.get(Calendar.AM_PM) == Calendar.PM) {
                                timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + "pm");
                            } else {
                                timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + "am");
                            }
                        }

                    }

                } catch (Exception e) {
                    // TODO: handle exception
                } finally {
                    //also call the same runnable to call it at regular interval
                    if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_segment_seconds))) {
                        handler.postDelayed(this, 1000);
                    } else {
                        handler.postDelayed(this, (60 - Calendar.getInstance().get(Calendar.SECOND)) * 1000);
                    }

                }
            }
        };
        handler.postDelayed(runnable, (1 - Calendar.getInstance().get(Calendar.MILLISECOND)) * 1000);

    }


}

The error is happening on the following line in the TimeModule class: Preferences sharedPreferences = new Preferences(this);

I believe it's something to do with the fact that a standard Java class doesn't have context until an onCreate() method is called, however I'm clueless as to what goes next. I've tried a few things but no luck.

The Java Class TimeModule is simply a Java Class, rather than a Class linked to a layout. The erason it extends Activity is so I can access certain methods such as getResources()

what happens if you have 'this' to 'getApplicationContext();' — letsCode, Feb 05 '18 at 20:14
Making TimeModule an Activity is not a good idea. Pass the Context of Template1Activity instead, e.g. via the Constructor. — Bö macht Blau, Feb 05 '18 at 20:17
On the same line the current issue persists, this is the new error: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference — Luke C, Feb 05 '18 at 20:17
I assume you mean like this @0X0nosugar? Because if so, it still produces an error: > Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference https://hastebin.com/oxavuhulas.cpp — Luke C, Feb 05 '18 at 20:24
never create an instance of Activity. You should **never** do this. Only system can do it. — Vladyslav Matviienko, Feb 05 '18 at 20:26
The other issue is that one can't make use of the Template1Activity as a kind of Context before it is fully initialised. So you have to initialise the TimeModule instance in onCreate() of Template1Activity or later — Bö macht Blau, Feb 05 '18 at 20:27
@0X0nosugar Thanks! Along with this I also did what the accepted answer told me to. — Luke C, Feb 05 '18 at 20:33

score 1 · Accepted Answer · answered Feb 05 '18 at 20:20

1

Since you are creating the TimeModule object yourself in Template1Activity . Use a constructor to pass in the context of Template1Activity to it. Then you can initialise the the sharedPreference in the constructor.

TimeModule(Context context){
    sharedPreferences = new Preferences(this);
}

answered Feb 05 '18 at 20:20

Ememobong AkpanEkpo

602
7
19

Thanks! This worked. I put Activity activity instead of Context context. Silly me. – Luke C Feb 05 '18 at 20:33

score 0 · Answer 2 · answered Feb 05 '18 at 20:22

0

Using getResources() in non-activity class you can use the ideas given in the answers instead of inhering activity.
it's not good idea passing contexts it might cause memory leaks.

answered Feb 05 '18 at 20:22

Amr

1,068
12
21

Passing in context to a Java Class - Android

2 Answers2