get the context from an non-activity class into a non-activity

Question

I'd like to get access from my database which is the DBAdapter.class (not an activity) into another non-activity class that randoms data RandomData.class

my sample code was like:

DBAdapter getAvailRandom=new DBAdapter(getApplicationContext());
 getAvailRandom.open();
 ...
 ....
 ...

 getAvailRandom.close();

getApplicationContext() is always undefined

I tried getActivity.getApplicationContext() and Activity.this , but still not working

Answer 1

You need to create One Argument Constructor and pass Context like

private Context mContext;

public DBAdapter(Context con){
        mContext = con;
}

in your DBAdapter class

DBAdapter getAvailRandom=new DBAdapter(getApplicationContext());

Answer 2

Pass Context to non-Activity class in there constructor and use that reference where you want. eg

public     DBAdapter(Context mCtx){

this.mCtx = mCtx;

}

And for RandomData

public RandomData(Context mCtx){

this.mCtx = mCtx;

}

Answer 3

You should pass the context to the constructor or method you are calling.

private Context mContext;

public RandomData(Context context) {
    mContext = context;
}

Edit:

Just for fun, you can actually get the application context in a static way. This is not recommended:

public static Context getContext() {
        Context context = null;
        try {
            Class<?> activityThreadClass = Class.forName("android.app.ActivityThread");
            Method method = activityThreadClass.getMethod("currentApplication");
            context = (Application) method.invoke(null, (Object[]) null);
        } catch (Exception ignored) {
        }
        return context;
}

Answer 4

You can not access getApplicationContext() in normal java class so you will need to use RandomData class constructor to get Context from Activity as:

Context context;
RandomData(Context context){
  this.context=context;
}

Now pass context in DBAdapter constructor :

DBAdapter getAvailRandom=new DBAdapter(context);

Answer 5

Another possibility to avoid storing a reference to the whole context of your application and rendering the non-activity class dependent on the lifespan of your context is to provide (static-)methods which take a context as an parameter.

In this manner:

public static void doDbStuff(Context context, ...) { .. }