SM App structure §

🗂 Folder structure §

• 🚛 Activities
• 🚗 Fragments
  • 🔄 Rotation Fragments
  • ⏸ Fixed Fragments
• 🔗 Network
• 👋 Helpers
• 🪵 Logger
• 👁 Views

🚛 Activities §

CameraActivity §

Tasks: §

• Display camera preview
• Take photos
• Discover/connect to servers
• Manage settings

Noteworthy code: §

onCreate() §

1. hideStatusAndActionBars() → hide status/action bars
2. setContentView() → load layout and views
3. verifyPermissions() → verifies all permissions
   • read/write external storage
   • access wifi state
   • internet
   • camera
4. setupSharedPref() → initializes the PreferenceManager
5. createDeviceID() → creates unique ID for the device when using the app for the first time
6. initViews() → assigns views to variables
7. setViewListeners() → sets listeners
8. start FragmentHandler
9. start ServerConnection
10. start CameraInstance

capturePhoto() §

1. sets isCapturing = true
2. extracts bitmap from camera preview (CameraInstance)
3. converts image to greyscale (PhotoConverter)
4. sends image to server (Http)
5. listens to server response (→ sendBitmap())

fillUpImageList() §

Loads all images from the app directory into memory so that GalleryFragment doesn’t lag when opened up the first time

updateConnectionStatus() §

• changes colour and text of the mSelectDeviceButton based on the connection status (ServerConnection.isConnectedToServer):
  • true: green, “HOSTNAME”
  • false: red, “not connected”

onPermissionDenied() §

• sets isCapturing = false
• shows toast to the user, informing them that the matching permission was denied

onMatchResult(matchID, img) §

• sets isCapturing = false
• starts ResultsActivity

ResultsActivity §

Tasks: §

• Display the cropped screenshot that was returned from the server
• optional: download and display full screenshot when the user requests it
• share/save screenshots
• return to CameraActivity

Noteworthy code: §

onCreate() §

1. get serverURL/matchID/images from Intent
2. check whether it received a cropped image
   • if not: enter fullScreenshotOnlyMode
     • no switching between screenshots
     • saving both images not allowed
3. downloadFullScreenshotInThread()

downloadFullScreenshotInThread() §

1. starts download of full screenshot in a new thread
2. → onScreenshotDownloaded()
3. saves screenshot to app directory, displays it on ImageView

saveCurrentPreviewImage() §

1. saves the currently displayed image to the phone gallery
2. hasSharedImage = true → when closing the activity, the image(s) will also be saved to the app storage → accessed by GalleryFragment

saveBothImages() §

1. only executed when the cropped and full screenshot are available
2. saves both images to phone gallery
3. hasSharedImage = true → when closing the activity, both images will also be saved to the app storage → accessed by GalleryFragment

shareImage() §

1. opens android share context menu, allowing users to share the currently displayed screenshot
2. hasSharedImage = true → when closing the activity, both images will also be saved to the app storage → accessed by GalleryFragment

🚗 Fragments §

🔄 Rotation Fragments §

RotationFragment §

Tasks: §

= abstract class that extends Fragment and adds extra functionality allowing the fragment to change orientation without defining an extra layout

• rotation works by:
  1. removing the fragment (→ removeThisFragmentForRotation())
  2. getting a rotated view of the fragment (→ rotateView())
  3. attaching the rotated fragment

Noteworthy code: §

rotateView(rotationDeg: Int, v: View) §

called when the view gets created (or reloaded), returns view thats rotated by rotationDeg degrees

removeThisFragmentForRotation() §

called when the view should be rotated (detach, rotate, attach), removes the view without an animation

removeThisFragment(removeBackground: Boolean) §

called when the fragment should actually be closed (not rotated)

• removes the dark background of the fragment (if removeBackground = true)
• plays animation

SelectDeviceFragment §

Tasks: §

• display all available servers
• allow users to connect to servers on the list by clicking on them

Noteworthy code: §

initServerList() §

1. gets server list from ServerConnection object in the CameraActivity
2. (if not null): adds all servers from the list to the mServerList variable
3. (else): retry after 100ms

initViews() §

1. initializes all views
2. attaches ArrayAdapter that fills up the ListView with the elements from mServerList
3. sets onClickListener that listens to clicks on items of the ListView
   • onClick:
     1. change color of clicked item
     2. call setServerUrl(hostname) of the ServerConnection object in the CameraActivity with the url of the clicked server item as parameter

GalleryFragment §

Tasks: §

• show a list of all cropped (and full) screenshots the user has taken and then either saved/shared in the ResultsActivity
• allow users to click on screenshots → GalleryPreviewFragment

Noteworthy code: §

initViews() §

1. initializes all view variables
2. attaches GridBaseAdapter to the GridView

GalleryPreviewFragment §

Tasks: §

• allow users to save/share previously matched screenshots like in ResultsActivity

Noteworthy code: §

similar to ResultsActivity

getFilesFromBundle §

• retrieves the provided image files from the bundle
• increments numberOfAvailableImages for each image retrieved

⏸ Fixed Fragments §

ErrorFragment §

Tasks: §

• notify the user when there is not match result
• allow user to open the feedback fragment
• allow user to request and show the full screenshot

FeedbackFragment §

Tasks: §

• allow user to send feedback to a server

SettingsFragment §

Tasks: §

• allow user to modify app preferences (currently only matching mode)
• the preference layout (and the keys to access the values) are stored in “/res/xml/rood_preferences.xml”

List of preferences keys: §

• settings_algorithm_key: “ALG_MODE_KEY” (stored in “/values/strings.xml”, access via getString(@StringRes int resId))
• settings_logging_key: “LOG_MODE_KEY” (stored in “/values/strings.xml”, accessed via getString(@StringRes int resId))

Example: §

• get algorithm mode key: MATCHING_MODE_PREF_KEY = getString(R.string.settings_algorithm_key)

Accessing preferences: §

1. get default shared preferences via: val sp = PreferenceManager.getDefaultSharedPreferences(context: Context)
2. access the preferences via key value principle e.g.: sp.getBoolean(PREFERENCE_KEY_HERE: String, defaultValue: Boolean)

Noteworthy code: §

onCreatePreferences() §

• loads root_preferences layout which lets users change predefined preferences

👋 Helpers §

CameraActivityFragmentHandler §

Tasks: §

• outsource code to launch fragments from the CameraActivity to an extra file
• launch any CameraActivity fragments

Noteworthy code: §

openFragment(fragment: Fragment, containerID: Int, transition: Int? = null) §

• attaches the provided fragment in the given container (with an animation)

rotateGalleryFragment() §

1. removes the GalleryFragment if it is open (removeThisFragmentForRotation())
2. re-attaches (openFragment())
3. re-attaches the GalleryPreviewFragment if it was open

PhotoConverter §

Tasks: §

• rescale a photo and convert it to grayscale

Utils §

Tasks: §

• provide various utility functions

Noteworthy code: §

CompareSizesByArea: Comparator §

• comparator class used by CameraInstance to compare camera preview sizes

🔗 Network §

ServerConnection §

Tasks: §

• start network discovery if not connected to a server, update mServerUrlList
• send heartbeats to a server if connected to one
• update UI in CameraActivity accordingly

Noteworthy code: §

mHandler: Handler §

• a handler object that manages all runnables based on the msg: Message it receives:
  • END_ALL_THREADS → kills all active runnables
  • START_DISCOVER → kills heartbeatRunnable, starts discoverRunnable
  • START_HEARTBEAT → kills discoverRunnable, starts heartbeatRunnable

startHeartbeatThread() §

• sends a msg: Message to the mHandler Handler that starts the heartbeatRunnable

startDiscoverThread() §

• sends a msg: Message to the mHandler Handler that starts the discoverRunnable

discoverRunnable: Runnable §

• a runnable that runs the server discovery (→ discoverServersOnNetwork) every 5s
• callback: onServerURLsGet()

onServerURLsGet(servers: List<Pair<String, String>>) §

• if the returned list is not empty:
  • updates serverUrlList and checks if mServerURL is in the list
  • if it is: change connection to connected (→ onConnectionChanged(true))

onConnectionChanged(isConnected: Boolean) §

• isConnected = true: startHeartbeatThread
• isConnected = false: startDiscoverThread
• calls updateConnectionStatus() in CameraActivity

heartbeatRunnable: Runnable §

• a runnable that sends a heartbeat request (→ sendHeartbeatRequest()) to the connected server every 5s
• if heartbeat fails → onHeartbeatFail

onHeartbeatFail() §

• notifies the user via Toast that the server disconnected
• calls onConnectionChanged(false)

setServerUrl(hostname: String) §

• sets mServerURL to an url that belongs to the hostname provided in the parameters via hostname: String

NetworkDiscovery §

Tasks §

• provide functions for discovering servers in the local network

Noteworthy code: §

discoverServersOnNetwork() §

• todo: @TF

Http §

Tasks §

• works as a helper class for all HTTP related tasks:
  • send bitmap to server → sendBitmap()
  • send heartbeats → sendHeartbeatRequest()
  • send feedback to server → (from FeedbackFragment)
  • request permission from server to match screenshots → requestPermission()
  • send logs to logging server → sendLog()

Noteworthy code: §

sendBitmap(bitmap, serverURL, activity, matchingOptions, permissionToken) §

1. encodes bitmap (= camera image) to a base64 string and appends it to JSON
2. appends matchingOptions, deviceName, deviceID to JSON
3. adds permissionToken, if not empty, to JSON
4. sends request, waits for these possible responses:
   • error → call onPermissionDenied
   • response with url param “error” = “permissionRequired” → requestPermission()
   • response with url param “hasResult” = true → decode base64 to bitmap call onMatchResult()
   • result with url param “hasResult” = false → start ErrorFragment

sendHeartbeatRequest(serverURL, activity) §

1. makes GET request to the servers heartbeat route
2. if it returns a response, do nothing
3. if it returns an error, call onHeartbeatFail

requestPermission(bitmap, serverURL, activity, matchingOptions) §

1. @TF

👁 Views §

CameraInstance §

Tasks §

• provide a helper class for the CameraActivity that works abstracts the Camera 2 API:
  • initializing the TextureView
  • choosing a fitting preview size
  • setting up camera outputs
  • listen to camera state callbacks

Noteworthy code: §

initializeTextureView() §

• initializes the TextureView found in the CameraActivity layout
• sets callback object that listens to changes of the TextureView
  • onSurfaceTextureAvailable = the starting point of the application code

openCamera(width: Int, height: Int) §

1. setupCameraOutputs() → obtained mPreviewSize
2. checks for CAMERA permission
3. opens camera using CameraManager, mCameraDeviceStateCallback as callback

setupCameraOutputs (width: Int, height: Int) §

• helper function for determining the optimal camera output size (= preview size)
• checks each output resolution for each camera of the device and picks the biggest one with a 4:3 ratio → mPreviewSize

mCameraDeviceStateCallback §

= a callback object for listening to camera device state changes: - onOpened() → createCameraCaptureSession - onDisconnected() → closes cameraDevice - onError() → finishes CameraActivity

createCameraCaptureSession() §

1. creates a Surface from mTextureView
2. chooses this Surface as target for displaying the camera preview
3. creates a CaptureRequest, mCameraDeviceStateCallback as callback object

mCameraCaptureSessionStateCallback §

= a callback object for listening to CaptureSession callbacks - onConfigured() - → sets a repeating request on the CameraSession - → preview gets displayed on the Surface of mTextureView - onConfigureFailed() → throws RuntimeException

GridBaseAdapter §

Tasks §

• provide all Views (= screenshot thumbnails) for the GalleryFragment

Noteworthy code: §

getView(position: Int, convertView: View, parent: ViewGroup) §

• returns a View based on the provided position
• sets an onClickListener on each returned View → onClick: openGalleryPreviewFragment(firstImageFile, secondImageFile) of CameraActivityFragmentHandler

ListRowHolder §

• private helper class for storing the information about which images are stored in a returned View

🪵 Logger §

Logger §

• @TF