package com.xengar.android.weather;

import android.content.Context;
import android.content.res.TypedArray;
import android.preference.EditTextPreference;
import android.util.AttributeSet;

public class LocationEditTextPreference extends EditTextPreference {
    static final private int DEFAULT_MINIMUM_LOCATION_LENGTH = 2;
    private int mMinLength;

    public LocationEditTextPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = context.getTheme().obtainStyledAttributes(
                attrs,
                R.styleable.LocationEditTextPreference,
                0, 0);
        try {
            mMinLength = a.getInteger(R.styleable.LocationEditTextPreference_minLength,
                    DEFAULT_MINIMUM_LOCATION_LENGTH);
        } finally {
            a.recycle();
        }
    }
}

package com.xengar.android.weather;

import android.app.AlertDialog;
import android.app.Dialog;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.preference.EditTextPreference;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.AttributeSet;
import android.widget.Button;
import android.widget.EditText;

public class LocationEditTextPreference extends EditTextPreference {
    static final private int DEFAULT_MINIMUM_LOCATION_LENGTH = 2;
    private int mMinLength;

    public LocationEditTextPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = context.getTheme().obtainStyledAttributes(
                attrs,
                R.styleable.LocationEditTextPreference,
                0, 0);
        try {
            mMinLength = a.getInteger(R.styleable.LocationEditTextPreference_minLength,
                    DEFAULT_MINIMUM_LOCATION_LENGTH);
        } finally {
            a.recycle();
        }
    }


    @Override
    protected void showDialog(Bundle state) {
        super.showDialog(state);

        EditText et = getEditText();
        et.addTextChangedListener(new TextWatcher() {


            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {
                Dialog d = getDialog();
                if (d instanceof AlertDialog) {
                    AlertDialog dialog = (AlertDialog) d;
                    Button positiveButton = dialog.getButton(AlertDialog.BUTTON_POSITIVE);
                    // Check if the EditText is empty
                    if (s.length() < mMinLength) {
                        // Disable OK button
                        positiveButton.setEnabled(false);
                    } else {
                        // Re-enable the button.
                        positiveButton.setEnabled(true);
                    }
                }
            }
        });
    }
}
Use AlertDialog with EditTextPreference and TextWatcher to disable setting the preference if the location is too short.
Use AlertDialog with EditTextPreference and TextWatcher to disable setting the preference if the location is too short.
