Validating EditTextPreference on Android

Add setOnPreferenceChangeListener for EditTextPreference after addPreferencesFromResource to validate data input for User:

EditTextPreference edit_Pref = (EditTextPreference) 
                    getPreferenceScreen().findPreference("geofence_range");
   edit_Pref.setOnPreferenceChangeListener(new OnPreferenceChangeListener() {

     @Override
      public boolean onPreferenceChange(Preference preference, Object newValue) {
          // put validation here..
            if(<validation pass>){
              return true;
            }else{
              return false;
             }
       }
    });

Note: This answer is based on the deprecated android.preference.EditTextPreference.

---

Huh. Another one of those things that should be so darned easy in Android but isn't. Other answers just silently prevent writing back the result to preferences, which seems a bit shoddy. (Showing toast is less shoddy, but is still shoddy).

You'll need a custom preference to do this. Customize onValidate to suit your needs.

package com.two_play.extensions;

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;
import android.preference.EditTextPreference;
import android.util.AttributeSet;
import android.view.View;
import android.widget.EditText;

public class ValidatingEditTextPreference extends EditTextPreference {
    public ValidatingEditTextPreference(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    public ValidatingEditTextPreference(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public ValidatingEditTextPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public ValidatingEditTextPreference(Context context) {
        super(context);
    }

    @Override
    protected void showDialog(Bundle state) {
        super.showDialog(state);
        AlertDialog dlg = (AlertDialog)getDialog();
        View positiveButton = dlg.getButton(DialogInterface.BUTTON_POSITIVE);
        getEditText().setError(null);
        positiveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                onPositiveButtonClicked(v);
            }
        });
    }

    private void onPositiveButtonClicked(View v) {
        String errorMessage = onValidate(getEditText().getText().toString());
        if (errorMessage == null)
        {
            getEditText().setError(null);
            onClick(getDialog(),DialogInterface.BUTTON_POSITIVE);
            getDialog().dismiss();
        } else {
            getEditText().setError(errorMessage);
            return; // return WITHOUT dismissing the dialog.
        }
    }

    /***
     * Called to validate contents of the edit text.
     *
     * Return null to indicate success, or return a validation error message to display on the edit text.
     *
     * @param text The text to validate.
     * @return An error message, or null if the value passes validation.
     */
    public String onValidate(String text)
    {
        try {
            Double.parseDouble(text);
            return null;
        } catch (Exception e)
        {
            return getContext().getString(R.string.error_invalid_number);
        }
    }
}