Module 6: Introduction to App Development

Lesson 16: Designing the App's Architecture

Objective: Plan the architecture of the family photo-sharing app, including the user interface, data storage, and basic features.

Overview of the App Structure:

The family photo-sharing app will allow users to upload, store, and share photos with family members. The core components of the app include:

• User Interface: A simple, text-based interface where users can register, log in, create albums, and upload/view photos.
• Data Storage: Data such as user profiles, albums, and photos will be stored in linked lists and files.
• Basic Features: User registration, album creation, photo uploading, and viewing will be implemented first.

Designing the Data Structures:

Let’s revisit the key data structures we’ll use to represent users, albums, and photos:

type
  PPhoto = ^TPhoto;
  TPhoto = record
    FileName: String;
    DateUploaded: TDateTime;
    Next: PPhoto;
  end;

  PAlbum = ^TAlbum;
  TAlbum = record
    Name: String;
    Photos: PPhoto;
    Next: PAlbum;
  end;

  PUser = ^TUser;
  TUser = record
    Name: String;
    Password: String;
    Albums: PAlbum;
    Next: PUser;
  end;

Explanation:

• TPhoto: represents a photo, including its file name, upload date, and a pointer to the next photo in the album.
• TAlbum: represents an album, including its name, a pointer to its photos, and a pointer to the next album.
• TUser: represents a user, including their name, password, a pointer to their albums, and a pointer to the next user.

Exercise - Implementing the Data Structures:

Implement the data structures above in Pascal. Ensure that the pointers are correctly set up to allow the dynamic linking of users, albums, and photos.

Lesson 17: Building the Core Functionality

Objective: Start building the core functionality of the app, including user registration, album creation, and photo uploading.

User Registration:

We’ll begin by allowing users to register. Here’s a simple function to register a new user:

function RegisterUser(var Head: PUser; Name, Password: String): PUser;
var
  NewUser: PUser;
begin
  New(NewUser);
  NewUser^.Name := Name;
  NewUser^.Password := Password;
  NewUser^.Albums := nil;
  NewUser^.Next := Head;
  Head := NewUser;
  RegisterUser := NewUser;
end;

Explanation:

• New(NewUser); allocates memory for the new user.
• NewUser^.Name := Name; assigns the user’s name.
• NewUser^.Password := Password; assigns the user’s password.
• NewUser^.Albums := nil; initializes the user’s albums to nil.
• NewUser^.Next := Head; links the new user to the head of the user list.
• Head := NewUser; updates the head of the user list to the new user.

Album Creation:

Next, we’ll implement album creation for each user:

procedure CreateAlbum(var User: PUser; AlbumName: String);
var
  NewAlbum: PAlbum;
begin
  New(NewAlbum);
  NewAlbum^.Name := AlbumName;
  NewAlbum^.Photos := nil;
  NewAlbum^.Next := User^.Albums;
  User^.Albums := NewAlbum;
end;

Explanation:

• New(NewAlbum); allocates memory for the new album.
• NewAlbum^.Name := AlbumName; assigns the album’s name.
• NewAlbum^.Photos := nil; initializes the photo list to nil.
• NewAlbum^.Next := User^.Albums; links the new album to the user’s existing albums.
• User^.Albums := NewAlbum; updates the user’s album list to include the new album.

Photo Uploading:

We’ll also need functionality for users to upload photos to their albums:

procedure UploadPhoto(var Album: PAlbum; FileName: String; DateUploaded: TDateTime);
var
  NewPhoto: PPhoto;
begin
  New(NewPhoto);
  NewPhoto^.FileName := FileName;
  NewPhoto^.DateUploaded := DateUploaded;
  NewPhoto^.Next := Album^.Photos;
  Album^.Photos := NewPhoto;
end;

Explanation:

• New(NewPhoto); allocates memory for the new photo.
• NewPhoto^.FileName := FileName; assigns the file name of the photo.
• NewPhoto^.DateUploaded := DateUploaded; records the upload date of the photo.
• NewPhoto^.Next := Album^.Photos; links the new photo to the beginning of the album’s photo list.
• Album^.Photos := NewPhoto; updates the album’s photo list to include the new photo.

Exercises:

• Implement the user registration, album creation, and photo uploading features as described above. Test each feature to ensure it works correctly.
• Create a simple menu system that allows users to choose between registering, creating albums, and uploading photos. Use a loop to keep the menu running until the user decides to exit.

Viewing Photos:

Finally, users should be able to view the photos they’ve uploaded. Here’s a simple procedure to list all photos in an album:

procedure ViewPhotos(Album: PAlbum);
var
  Temp: PPhoto;
begin
  Temp := Album^.Photos;
  while Temp <> nil do
  begin
    writeln('Photo: ', Temp^.FileName, ' Uploaded on: ', DateTimeToStr(Temp^.DateUploaded));
    Temp := Temp^.Next;
  end;
end;

Explanation:

• Temp := Album^.Photos; starts at the first photo in the album.
• while Temp <> nil do: loops through the photo list until the end is reached.
• writeln(...); prints the file name and upload date of each photo.
• Temp := Temp^.Next; moves to the next photo in the list.

Exercise - Implementing Photo Viewing:

Implement the photo viewing feature and test it by creating an album, uploading photos, and then listing them.

Next Steps:

In the next module, we’ll expand the app with more advanced features, such as user authentication, sharing photos with specific users, and managing privacy settings.