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smd:laboratoare:04 [2021/04/08 11:20] alexandru.chirvase [Threading in Android] |
smd:laboratoare:04 [2021/05/12 17:46] (current) adriana.draghici [Tasks] |
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| :!: Calling methods from the Android UI API must be done on the UI thread. For example, if you want to show a toast from a worker-thread, use [[https://developer.android.com/reference/android/app/Activity#runOnUiThread(java.lang.Runnable)|runOnUiThread]]. | :!: Calling methods from the Android UI API must be done on the UI thread. For example, if you want to show a toast from a worker-thread, use [[https://developer.android.com/reference/android/app/Activity#runOnUiThread(java.lang.Runnable)|runOnUiThread]]. | ||
| - | Regarding the relationship between the threading components and the **lifecycle** of the UI components (activities and fragments), certain threading objects can be tied and other not. The IntentServices we discussed in Lab3 are not tied to the activities or fragments lifecycle, but the AsyncTasks (Android specific threading components), are terminated when the UI components are destroyed. | + | Regarding the relationship between the threading components and the **lifecycle** of the UI components (activities and fragments), certain threading objects can be tied to the UI lifecycle and other not. The IntentServices we discussed in Lab3 are not tied to the activities or fragments lifecycle, but the AsyncTasks (Android specific threading components), are terminated when the UI components are destroyed. |
| In [[smd:laboratoare:03#using_intent_services|Lab 3]] we presented IntentServices which also run on separate threads. The mechanisms we will focus on this lab, some of them you might be familiar with from Java: | In [[smd:laboratoare:03#using_intent_services|Lab 3]] we presented IntentServices which also run on separate threads. The mechanisms we will focus on this lab, some of them you might be familiar with from Java: | ||
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| We will also briefly discuss AsyncTasks, which are not recommended and will be deprecated in the next Android release (R). | We will also briefly discuss AsyncTasks, which are not recommended and will be deprecated in the next Android release (R). | ||
| - | Because the SMD labs' scope do not include learning a new language, we will not address in this lab asynchronous programming using the **[[https://developer.android.com/topic/libraries/architecture/coroutines|coroutines]]** provided in **Kotlin**. Nonetheless, if you want to learn and code in Kotlin, or are already familiar with it, feel free to use them in your project. Useful video overview: [[https://www.youtube.com/watch?v=BOHK_w09pVA|Understand Kotlin Coroutines on Android (Google I/O'19)]]. | + | <note tip>Because this course's scope does not include learning a new language, we will not address in this lab asynchronous programming using the **[[https://developer.android.com/topic/libraries/architecture/coroutines|coroutines]]** provided in **Kotlin**. Nonetheless, if you want to learn and code in Kotlin, or are already familiar with it, feel free to use them in your project. Useful video overview: [[https://www.youtube.com/watch?v=BOHK_w09pVA|Understand Kotlin Coroutines on Android (Google I/O'19)]]. |
| + | </note> | ||
| Other threading mechanisms you can use and are not covered in this lab: | Other threading mechanisms you can use and are not covered in this lab: | ||
| * **Reactive programming** using **[[https://blog.gojekengineering.com/multi-threading-like-a-boss-in-android-with-rxjava-2-b8b7cf6eb5e2|RxJava]]** or **RxKotlin** - do not need to explicitly create threads, just choose a scheduler | * **Reactive programming** using **[[https://blog.gojekengineering.com/multi-threading-like-a-boss-in-android-with-rxjava-2-b8b7cf6eb5e2|RxJava]]** or **RxKotlin** - do not need to explicitly create threads, just choose a scheduler | ||
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| === Using Handlers === | === Using Handlers === | ||
| We need a **messaging mechanism between threads**, and Android offers [[https://developer.android.com/reference/android/os/Handler|Handlers]]. These are closely connected to other objects needed for messaging: | We need a **messaging mechanism between threads**, and Android offers [[https://developer.android.com/reference/android/os/Handler|Handlers]]. These are closely connected to other objects needed for messaging: | ||
| - | * [[https://developer.android.com/reference/android/os/Looper|Looper]] - provided to a Handler, it runs the message queue in a loop | + | * [[https://developer.android.com/reference/android/os/Looper|Looper]] - provided to a Handler, keeps a thread alive, loops through MessageQueue and sends Messages to the corresponding Handler to process it |
| * [[https://developer.android.com/reference/android/os/Message|Message]] - the message to be sent to a Handler | * [[https://developer.android.com/reference/android/os/Message|Message]] - the message to be sent to a Handler | ||
| * [[https://developer.android.com/reference/android/os/MessageQueue|MessageQueue]] - the messages dispatached to a Looper, the developer doesn't interact directly with it, most interaction is through the Handler class | * [[https://developer.android.com/reference/android/os/MessageQueue|MessageQueue]] - the messages dispatached to a Looper, the developer doesn't interact directly with it, most interaction is through the Handler class | ||
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| ===Task 2 (4p)=== | ===Task 2 (4p)=== | ||
| - | Mock the download of several files (at least 10) in parallel on multiple threads using Runnables and ThreadPoolExecutor ([[https://developer.android.com/reference/java/util/concurrent/ThreadPoolExecutor|documentation]], [[https://developer.android.com/training/multiple-threads/create-threadpool#ThreadPool|creation example]]). | + | Mock the download of several files (at least 10) in parallel on multiple threads using Runnables and ThreadPoolExecutor ([[https://developer.android.com/reference/java/util/concurrent/ThreadPoolExecutor|documentation]], [[https://www.journaldev.com/1069/threadpoolexecutor-java-thread-pool-example-executorservice|example]]). |
| * For the "mock" download, each thread should sleep a random number between 100 and 200 ms. | * For the "mock" download, each thread should sleep a random number between 100 and 200 ms. | ||
| * The UI should update in real time a text view with the following content: | * The UI should update in real time a text view with the following content: | ||
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| … | … | ||
| </code> | </code> | ||
| - | * The text view must have the option android:inputType="textMultiLine". | + | * To show multiple line you can add the ''android:inputType="text"'' to the TextView |
