/*
 * Copyright (c) 2016. Libero Strategies, LLC - All Rights Reserved
 * Unauthorized copying of this file, via any medium is strictly prohibited
 * Proprietary and Confidential
 */

package com.example.android.sunshine.app;

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

/**
 * Created by pink on 11/14/2016.
 */

public class LocationEditTextPreference extends EditTextPreference {
    private static final 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();
        }
    }
}

/*
 * Copyright (c) 2016. Libero Strategies, LLC - All Rights Reserved
 * Unauthorized copying of this file, via any medium is strictly prohibited
 * Proprietary and Confidential
 */

package com.example.android.sunshine.app;

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;

/**
 * Created by pink on 11/14/2016.
 */

public class LocationEditTextPreference extends EditTextPreference {
    private static final 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 ed = getEditText();
        ed.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 EditText is empty.
                    if (s.length() < mMinLength) {
                        // Disable OK button.
                        positiveButton.setEnabled(false);
                    } else {
                        // Re-enable the button.
                        positiveButton.setEnabled(true);
                    }
                }
            }
        });
    }
}

Implement limits in custom preference view.