Simple Gallery App in Android

I have recently worked on a simple Gallery application in Android.

It has one ImageView component, two buttons, previous and next and one TextView for description. It is a gallery application for European cars. Actually I have 27 car brands and one model (image) for each brand. I added 27 images which are all 640 x 480 pixels (You can download images from Google) into CarTestApp/res/drawable-mdpi folder.

I was testing my app on Nexus 7 AVD emmulator.

Here is how you application should look like.

I will show you some tricks I used in this small app, like how to access all drawable objects.

Ok so here is my layout file:

<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context=".MainActivity" android:orientation="vertical"> <ImageView android:id="@+id/main_image_view" android:layout_width="wrap_content" android:layout_height="wrap_content" android:contentDescription="@string/image_view" android:src="@drawable/alfa_romeo__giulietta" /> <LinearLayout android:layout_width="match_parent" android:layout_height="50dp" android:orientation="horizontal" > <TextView android:id="@+id/car_name_text_view" android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="center" android:text="@string/car_name_text_view" android:textAlignment="center" android:textSize="30sp" /> </LinearLayout> <LinearLayout android:layout_width="match_parent" android:layout_height="100dp" android:orientation="horizontal" > <Button android:id="@+id/prev_btn" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="225dp" android:text="@string/prev_btn" /> <Button android:id="@+id/next_btn" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/next_btn" /> </LinearLayout> </LinearLayout>

My strings.xml file

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">CartTestApp</string>
    <string name="action_settings">Settings</string>
    <string name="hello_world">Hello world!</string>
    <string name="image_view">Image description</string>
    <string name="prev_btn">prev</string>
    <string name="next_btn">next</string>
    <string name="car_name_text_view">Car Name</string>
</resources>

I added Utils.java file for a helper function. It is only one function but I guess I will expand the application future.

Utils.java:

package com.testpkg.carttestapp;

public class Utils {
    public static String formatFirstLetterOfString(String str) {
        String result = "";

        result = str.substring(0, 1).toUpperCase()
                + str.substring(1).toLowerCase();

        return result;
    }
}

Next class I added is called CarNames.java. It has many static functions so that I don't need to instantiate an object of this class. No need to.

Here it is:



package com.testpkg.carttestapp; import java.lang.reflect.Field; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Random; import com.testpkg.carttestapp.Utils; public class CarNames { public static Field[] nativeDrawables = android.R.drawable.class .getFields(); public static Field[] drawables = com.testpkg.carttestapp.R.drawable.class .getFields(); public static List<string> carStringsList = new ArrayList<string>(); public static List<integer> carIdsList = new ArrayList<integer>(); public static Map<Integer, String> carNamesList = new HashMap<Integer, String>(); public CarNames() { reset(); } public static String random() { String result; Random randomNum = new Random(); int index = randomNum.nextInt(carNamesList.size()); result = carNamesList.get(index); carNamesList.remove(index); return result; } private static String formatCarFieldName(String fieldName) { String result = ""; String[] brandsAndModels = fieldName.split("__"); String[] brandArr = brandsAndModels[0].split("_"); String[] modelArr = brandsAndModels[1].split("_"); for (int b = 0; b < brandArr.length; b += 1) { result += Utils.formatFirstLetterOfString(brandArr[b]) + " "; } result += "- "; for (int m = 0; m < modelArr.length; m += 1) { result += Utils.formatFirstLetterOfString(modelArr[m]) + " "; } return result; } public static void reset() { for (Field field : drawables) { try { if (!field.getName().equals("ic_launcher")) { carIdsList.add(field.getInt(field.getName())); carStringsList.add(formatCarFieldName(field.getName())); } } catch (Exception e) { e.printStackTrace(); } } for (int i = 0; i < carStringsList.size(); i += 1) { carNamesList.put(carIdsList.get(i), carStringsList.get(i)); } } }
Check these lines:

public static Field[] nativeDrawables = android.R.drawable.class
            .getFields();
public static Field[] drawables = com.testpkg.carttestapp.R.drawable.class
            .getFields();

Function getFields() returns the fields in a given resource from our application.

For example android.R.drawable contains native android drawable resources while com.testpkg.cartestapp.R.drawable contains drawable resources that we have added to our application.

So actually we can search our resources with code.

I have two ArrayList objects, one for drawable ids and one for drawable string names. I also have a hash map with drawable id as a key and car string name as a value.

Here is the reset() function in which I fill my lists and the hash map:

public static void reset() {

     for (Field field : drawables) {
            try {
                if (!field.getName().equals("ic_launcher")) {
                    carIdsList.add(field.getInt(field.getName()));
                    carStringsList.add(formatCarFieldName(field.getName()));
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        for (int i = 0; i < carStringsList.size(); i += 1) {
            carNamesList.put(carIdsList.get(i), carStringsList.get(i));
        }
    }

You may noticed this function formatCarFieldName(); I can use java function toUpperCase() but that will make all letters upper case. I don't want that, I wan only the first letter upper cased. Strings are immutable values so I make a concatenation trick like this one:

result = str.substring(0, 1).toUpperCase() + str.substring(1).toLowerCase();

which will upper case only the first letter. You can find this in the Utils class.

Some screen shots: