Android Studios如何将上下文从mainactivity传递到另一个类

Question

I have this problem, how do i use a function from MainActivity in my class Dialog_findname, i have to pass the context of main in line: vardadienas = main.loadedfile(MainActivity.this);

public class Dialog_findname extends AppCompatDialogFragment {

  private EditText findName;
  private findnameDialogListener listener;
  private List<VDienas> vardadienas = new ArrayList<>();
  private Finder finder = new Finder();
  private MainActivity main = new MainActivity();


  @Override
  public Dialog onCreateDialog(Bundle savedInstanceState) {

    vardadienas = main.loadedfile(MainActivity.this);
  }

And this is my MainActivity function I want to call in the other class:

public List<VDienas> loadedfile(Context ctxt){
    FileInputStream fis = null;
    try {
        fis = openFileInput(FILE_NAME);
        InputStreamReader isr = new InputStreamReader(fis);
        BufferedReader reader = new BufferedReader(isr);
        String line;
        reader.readLine();

        while ((line = reader.readLine()) != null){
            VDienas VissGads = new VDienas();
            String[] tokens = line.split(";");


            VissGads.setDatums(tokens[0]);
            VissGads.setMenesis(Integer.parseInt(tokens[1]));
            VissGads.setDiena(Integer.parseInt(tokens[2]));

            for (int i = 0; i < Integer.parseInt(tokens[3]); i++) {
                VissGads.setVards(tokens[i + 4]);

            }
            vardadienas.add(VissGads);
        }

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }finally {
        if (fis != null){
            try {
                fis.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return vardadienas;

}

I tried to look up for similar questions, but i still couldn't understand how to :(

Answer 1

i think, u have to call this Function on ur MainActivity.

vardadienas = main.loadedfile(this);

or check MainActivity.class

Answer 2

First , you can't create an Activity with the following:

private MainActivity main = new MainActivity();

it should be started with Context.startActivity() , you can read more about it at Activity documentation .

Second , you have the following method:

public List<VDienas> loadedfile(Context ctxt) {
  ...
}

so, you can't call it with the following inside of Fragment:

 vardadienas = main.loadedfile(MainActivity.this);

because MainActivity.this is referencing to instance of MainActivity but your fragment is not an instance of activity.

You need to call the method with the following:

 vardadienas = main.loadedfile(getContext());

where getContext() referring to Activity where the Fragment attached.

---

You better move the loadedfile(Context ctxt) to its own class as an util class so you can reuse the method from any other class. You can make something like this:

public class FileUtils {
  private FileUtils() {} // this prevent class being instantiate.

  // we need to make it static so it can be accessed without
  // creating an instance of the class.
  // of course, you can use singleton. But it's another topic
  public static List<VDienas> loadedfile(Context ctxt) {
    ...
  }
}

then you can use the method with something like this:

vardadienas = FileUtils.loadedfile(getContext());