Android - Read a File

问题

I am trying to read a list of exercises from a file Exercises.txt in my /assests folder and I've found plenty of examples how to, but I keep getting the error "context cannot be resolved" and if I manage to fix that, then I get "Default constructor cannot handle exception type IOException thrown by implicit super constructor. Must define an explicit constructor"

Here is my code:

class ChooseExercises extends ListActivity{

    String[] exercises;

    AssetManager am = context.getAssets();  //Error 1
    InputStream inputStream = am.open("test.txt"); //Error 2
    InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
    BufferedReader bufferedReader = new BufferedReader(inputStreamReader);

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        // TODO Auto-generated method stub
        super.onListItemClick(l, v, position, id);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.choose_exercises);
    }

}

Thank you all for assistance.

回答1:

Since there is nothing named context, you cannot refer to it from a data member initializer.

So, start by moving your AssetManager and subsequent data members into onCreate() as local variables, and replace context.getAssets() with just getAssets(), and you will be in better shape.

class ChooseExercises extends ListActivity{
    String[] exercises;

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        // TODO Auto-generated method stub
        super.onListItemClick(l, v, position, id);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.choose_exercises);

        AssetManager am = context.getAssets();  //Error 1
        InputStream inputStream = am.open("test.txt"); //Error 2
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);

        // TODO: actually use this stuff
    }
}

Later, as you get more comfortable with Java and Android, move this disk I/O into a background thread.

回答2:

I think you forgot to use a try-catch construction.

Writing:

try{
            FileOutputStream fos = getBaseContext().openFileOutput("fileName", Context.MODE_PRIVATE);
            ObjectOutputStream os = new ObjectOutputStream(fos);
            os.writeObject("content");
            os.close();
        }catch(Exception ex){
            //do stuff if something goes wrong.
        }finally{
            //do stuff in the end.
        }

Reading:

try{
        FileInputStream fis = getBaseContext().openFileInput("filename");
        ObjectInputStream is = new ObjectInputStream(fis);
        Object s = (Object) is.readObject(); // Object must be String if you want to read a string.
        is.close();
    }catch(Exception ex){
        //do stuff if something goes wrong.
    }finally{
        //do stuff in the end.
    }

来源：https://stackoverflow.com/questions/18069646/android-read-a-file