Question

I use SharedPreferences for storing data. When I try to call the data-storing function from the constructor of my class, it shows a Runtime error. However, when I call the function from onCreate() it works fine.
Is there any way I can call my data-storing function from the constructor?

package com.examples.storedata;

import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;

import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class Activity1 extends Activity 
{
    EditText editText1, editText2;
    TextView textSavedMem1, textSavedMem2;
    Button buttonSaveMem1, buttonSaveMem2;

    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main); 

        textSavedMem1 = (TextView)findViewById(R.id.savedmem1);
        textSavedMem2 = (TextView)findViewById(R.id.savedmem2);
        editText1 = (EditText)findViewById(R.id.edittext1);
        editText2 = (EditText)findViewById(R.id.edittext2);
        buttonSaveMem1 = (Button)findViewById(R.id.save_mem1);
        buttonSaveMem2 = (Button)findViewById(R.id.save_mem2); 
        buttonSaveMem1.setOnClickListener(buttonSaveMem1OnClickListener);
        buttonSaveMem2.setOnClickListener(buttonSaveMem2OnClickListener);
    }

    public Activity1()
    {
        LoadPreferences(); //show error while calling from here
    }

    Button.OnClickListener buttonSaveMem1OnClickListener
        = new Button.OnClickListener(){
            public void onClick(View arg0) {
                SavePreferences("MEM1", editText1.getText().toString());
                LoadPreferences();
            }
        };

    Button.OnClickListener buttonSaveMem2OnClickListener
        = new Button.OnClickListener(){
            public void onClick(View arg0) {
                SavePreferences("MEM2", editText2.getText().toString());
                LoadPreferences();
            }
        };


   private void SavePreferences(String key, String value)
   {
       SharedPreferences sharedPreferences = getPreferences(MODE_APPEND);
       SharedPreferences.Editor editor = sharedPreferences.edit();
       editor.putString(key, value);
       editor.putInt("1",5);
       editor.commit();
   }

   private void LoadPreferences()
   {
       SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
       String strSavedMem1 = sharedPreferences.getString("MEM1", "");
       String strSavedMem2 = sharedPreferences.getString("MEM2", "");
       textSavedMem1.setText(strSavedMem1);
       textSavedMem2.setText(strSavedMem2);
    }
}

Answer 1

You are attempting to access your text views before you have initialised the view or the variables:

textSavedMem1.setText(strSavedMem1);
textSavedMem2.setText(strSavedMem2);

When you call LoadPreferences from the Activity constructor, onCreate hasn’t yet been called, which means textSavedMem1 and textSavedMem2 have not been initialised and are null.

When you call it from onCreate, so long as it is after the following, then these variable are initialised and everything works as expected.

setContentView(R.layout.main); 

textSavedMem1 = (TextView)findViewById(R.id.savedmem1);
textSavedMem2 = (TextView)findViewById(R.id.savedmem2);