Try/catch Not Working Inside A Custom Class, Npe

Fairly simple. I have a BIG class for my main project, and it became 'unwieldy'. SO today I decided to try making my own class, so I could simplify some of the code in the big cla

Solution 1:

I believe the problem is that you are trying to call this method

openFileInput()

without giving it context which it needs. I still don't think you need to extend Activity but make this a regular class by removing extends Activity. Create an instance of this class when you need it in the calling Activity like

DataHandler data = DataHandler (this);  // give contextdata.retrieveData();

something like that to call the method. Then create a constructor in the class like

ublic classDataHandlerextendsActivity {

FileOutputStream file_out;
FileInputStream file_in;
ObjectOutputStream obj_out;
ObjectInputStream obj_in;
ArrayList<String> retrieved_data;
Context mContext;   // add Context variablepublicDataHandler(Context context){
mContext = context;   assign context
}

Then in your method use

publicArrayList<String> retrieveData(){

    try {   
        file_in = mContext.openFileInput("array_saved");
        obj_in = newObjectInputStream(obj_in);
        if(obj_in.available() > 0){
        retrieved_data = (ArrayList<String>) obj_in.readObject();
        }
        else{
            retrieved_data = newArrayList<String>();
            }

        obj_in.close();
        file_in.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

    return retrieved_data;

}

I believe something like this should help. The method openFileInput() is expecting a Context which is null at this point, hence the NPE. Passing a Context to the class will solve this problem as it will have the current Activity Context

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