Android ListView
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Questions and Answers

What is a characteristic of external storage?

  • It can be removed or transferred to another device if needed. (correct)
  • It is private to your app.
  • It is always present in every device.
  • It is wiped when the app is uninstalled in all cases.

    • What is required to read/write the device's external storage?

  • No permission is required.
  • Only read permission is required.
  • Explicit permission must be requested in the app's AndroidManifest.xml file. (correct)
  • The user's permission is not required.

    • What is a difference between internal and external storage?

  • External storage is always present in every device.
  • Internal storage is private to your app.
  • Internal storage is smaller than external storage. (correct)
  • External storage is private to your app.

    • What is used to read a file in internal storage?

    <p>Scanner</p> Signup and view all the answers

    What is used to write a short text file to internal storage?

    <p>PrintStream</p> Signup and view all the answers

    What happens to the external storage when the app is uninstalled?

    <p>It is not wiped in any case.</p> Signup and view all the answers

    What is the size of internal storage?

    <p>It is smaller than external storage.</p> Signup and view all the answers

    What is the purpose of openFileInput and openFileOutput methods?

    <p>To read and write files from internal storage.</p> Signup and view all the answers

    What is the purpose of passing a unique ID number to startActivityForResult?

    <p>To specify the request code for the result</p> Signup and view all the answers

    What happens when startActivityForResult is called?

    <p>The calling activity continues executing immediately</p> Signup and view all the answers

    What is the purpose of the onActivityResult method?

    <p>To check for the unique ID and retrieve extra data from the intent</p> Signup and view all the answers

    How does the called activity send a result back?

    <p>By calling setResult and finish</p> Signup and view all the answers

    What is the purpose of the Intent in the onActivityResult method?

    <p>To store extra data to be sent back</p> Signup and view all the answers

    Why is it necessary to modify the called activity to send a result back?

    <p>To allow the calling activity to retrieve the result</p> Signup and view all the answers

    What is the purpose of an adapter in a ListView?

    <p>To help turn list data into list view items</p> Signup and view all the answers

    What is the difference between a static list and a dynamic list?

    <p>Static lists are fixed and dynamic lists are generated at runtime</p> Signup and view all the answers

    What is the purpose of the android:entries attribute in a ListView?

    <p>To specify the array of options to appear in the list</p> Signup and view all the answers

    What is the default layout for lists in a ListView?

    <p>android.R.layout.simple_list_item_1</p> Signup and view all the answers

    What is the method used to attach an adapter to a ListView?

    <p>setAdapter()</p> Signup and view all the answers

    What is the type of array that can be used to create an ArrayAdapter?

    <p>Either String[] or ArrayList</p> Signup and view all the answers

    What is the purpose of the android:id attribute in a ListView?

    <p>To set the unique ID for the ListView for use in Java code</p> Signup and view all the answers

    What is the location of the file that contains the list of options for a dynamic list?

    <p>res/raw/oses.txt</p> Signup and view all the answers

    What method is used to check if the external storage is writable?

    <p>Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())</p> Signup and view all the answers

    What permission is required to access web data in Android?

    <p>INTERNET</p> Signup and view all the answers

    How are sound files referred to in Java code?

    <p>R.raw.filename</p> Signup and view all the answers

    What is the purpose of the setLooping method in MediaPlayer?

    <p>To control the looping of the media</p> Signup and view all the answers

    What is the purpose of the Scanner class in reading web data?

    <p>To read the data from a URL</p> Signup and view all the answers

    What is the purpose of the getCurrentPosition method in MediaPlayer?

    <p>To get the current position of the media</p> Signup and view all the answers

    What is the purpose of the isPlaying method in MediaPlayer?

    <p>To check if the media is playing</p> Signup and view all the answers

    How do activities communicate with each other in Android?

    <p>Through intents</p> Signup and view all the answers

    What is the primary difference between internal and external storage?

    <p>Internal storage is private to each app.</p> Signup and view all the answers

    What is the main purpose of the java.io.File class?

    <p>To represent a file or directory.</p> Signup and view all the answers

    What is the purpose of the getFilesDir() method?

    <p>To get the internal storage directory for the app.</p> Signup and view all the answers

    What is the purpose of the java.io.InputStream and OutputStream classes?

    <p>To represent flows of data bytes from a source or destination.</p> Signup and view all the answers

    What happens to the internal storage when an app is uninstalled?

    <p>It is wiped out.</p> Signup and view all the answers

    What is the purpose of the getResources().openRawResource(R.raw.id) method?

    <p>To read a raw resource file.</p> Signup and view all the answers

    How much storage is typically available in internal storage?

    <p>1-4 GB</p> Signup and view all the answers

    What is the purpose of the openFileInput("name", mode) method?

    <p>To read a file from internal storage.</p> Signup and view all the answers

    Study Notes

    ListView

    • An ordered collection of selectable choices
    • Key attributes in XML:
      • android:clickable to set the list to be clickable or not
      • android:id to assign a unique ID for use in Java code
      • android:entries to set the options to appear in the list, which must match an array in strings.xml

    Static Lists

    • Content is fixed and known before the app runs
    • Declare the list elements in the strings.xml resource file
    • Example: Android, iPhone, Max OS X

    Dynamic Lists

    • Content is read or generated as the program runs
    • Comes from a data file, internet, etc.
    • Must be set in Java code
    • Example: reading a file oses.txt to create a list

    List Adapters

    • Helps turn list data into list view items
    • Common adapters: ArrayAdapter, CursorAdapter
    • Syntax for creating an adapter: ArrayAdapter name = new ArrayAdapter(activity, layout, array);
    • Attach the adapter to the list by calling the setAdapter method of the ListView object in Java code

    Waiting for a Result

    • If the calling activity wants to wait for a result from the called activity:
      • Call startActivityForResult instead of startActivity
      • Pass a unique ID number to represent the action being performed
      • Write an onActivityResult method that will be called when the second activity is done
      • Check for the unique ID as was passed to startActivityForResult
      • Ask the intent for any extra data
      • Modify the called activity to send a result back using setResult and finish methods

    Files and Storage

    • Android can read/write files from two locations:
      • Internal storage
      • External storage

    Internal Storage

    • Built into the device
    • Guaranteed to be present
    • Typically smaller (~1-4 GB)
    • Can't be expanded or removed
    • Specific and private to each app
    • Wiped out when the app is uninstalled

    File and Streams

    • java.io.File represents a file or directory
    • Methods: canRead, canWrite, create, delete, exists, getName, getParent, getPath, isFile, isDirectory, lastModified, length, listFiles, mkdir, mkdirs, renameTo
    • java.io.InputStream, OutputStream represent flows of data bytes from/to a source or destination
    • Stream objects are often passed as a parameter to other objects like java.util.Scanner, java.io.BufferedReader, java.io.PrintStream to do the actual reading/writing

    Using Internal Storage

    • An activity has methods to read/write files:
      • getFilesDir() returns internal directory for the app
      • getCacheDir() returns a "temp" directory for scrap files
      • getResources().openRawResource(R.raw.id) reads an input file from res/raw/
      • openFileInput("name", mode) opens a file for reading
      • openFileOutput("name", mode) opens a file for writing
    • Can use these methods to read/write files on the device
    • Many methods return standard java.io.File objects
    • Some return java.io.InputStream or OutputStream objects, which can be used with standard classes like Scanner, BufferedReader, and PrintStream to read/write files

    Internal Storage Examples

    • Example 1: read a file and put its contents into a TextView
    • Example 2: write a short text file to the internal storage and read it back

    External Storage

    • External storage: Card that is inserted into the device (such as a MicroSD card)
    • Can be much larger than internal storage (~8-32 GB)
    • Can be removed or transferred to another device if needed
    • May not be present, depending on the device
    • Read/writable by other apps and users; not private to the app
    • Not wiped when the app is uninstalled, except in certain cases

    External Storage Permission

    • If the app needs to read/write the device's external storage, it must explicitly request permission to do so in the AndroidManifest.xml file
    • On install, the user will be prompted to confirm the app's permissions

    Checking if Storage is Available

    • isExternalStorageWritable() method to check if external storage is writable
    • isExternalStorageReadable() method to check if external storage is readable

    Accessing Web Data

    • To read data from the web, request the INTERNET permission in the AndroidManifest.xml file
    • Use the java.net.URL class to connect to a file or page at a given URL and read its data

    Playing Sound Effects

    • Find sound files such as .WAV, .MP3
    • Put sound files in the project folder app/src/main/res/raw
    • Refer to audio files in Java code as R.raw.filename
    • Load and play clips using Android's MediaPlayer class
    • Methods: create, start, stop, pause, isLooping, isPlaying, getCurrentPosition, release, seekTo, setDataSource, setLooping

    Multiple Activities

    • Many apps have multiple activities
    • Example: address book app with main activity for listing contacts and another activity for viewing details
    • An activity can launch another activity in response to an event
    • The activity can pass data to the other activity
    • The second activity can send data back to the first activity when it is done

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    Understanding the attributes and functionality of ListView in Android development.

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