Multi-thread programming and asynchronous processing in Android

Multithreaded programming and asynchronous processing in Android

Introduction

In mobile app development, user experience is paramount. A smooth, efficient app engages users and increases user satisfaction. However, mobile applications are faced with the challenges of handling complex business logic, responding to user input, handling network requests, and many other tasks. In order to ensure application performance and user experience, multi-threaded programming and asynchronous processing have become indispensable technical means.

In mobile applications, tasks involving time-consuming operations include but are not limited to: network requests, database operations, image loading, file reading and writing, etc. If these time-consuming operations are performed in the main thread of the application (also called the UI thread), it will cause the application interface to freeze, freeze, or even cause an application not responding (ANR) error. This negatively impacts the user experience, making the app feel slow and unresponsive, which reduces user satisfaction and loyalty.

In order to solve these problems, Android provides a mechanism for multi-threaded programming and asynchronous processing. Multi-threaded programming allows multiple threads to be executed simultaneously in the application, so that time-consuming operations can be separated from the UI thread to avoid blocking the UI thread. Asynchronous processing is a way to perform time-consuming operations in the background and return the results to the UI thread after the operation is complete, thereby maintaining the responsiveness of the application.

Therefore, in Android application development, it is very important to master multi-thread programming and asynchronous processing technology. They can improve application performance, guarantee user experience, and make applications more stable and reliable. Next, we will delve into the relevant content of multi-threaded programming and asynchronous processing in Android, so that developers can make full use of these technologies to build efficient and smooth mobile applications.

Multithreaded programming in Android

In Android, the main thread of the application is also called the UI thread, which is responsible for processing the UI operations of the application, including drawing the interface, processing user input, and updating the UI state. However, if time-consuming operations are performed in the UI thread, such as network requests, database operations, file reading and writing, etc., the UI thread will be blocked, resulting in freezing of the application interface and ANR (Application Not Responding) errors.

In order to avoid performing time-consuming operations in the UI thread, Android provides a multi-threaded programming method that allows multiple threads to be executed simultaneously in the application and separates time-consuming operations from the UI thread to ensure smoothness and responsiveness of the application. .

Multithreaded programming methods in Android include but are not limited to the following:

1. Thread: Thread is a thread class in Java and can also be used in Android applications. By creating a Thread object and overriding the run() method, time-consuming operations can be performed in a new thread, thereby avoiding blocking in the UI thread.

2. HandlerThread: HandlerThread is a special thread class in Android, inherited from Thread, and has a built-in Looper and Handler. It can conveniently handle the message passing and processing between threads, so as to realize the communication and cooperation between threads.

3. AsyncTask: AsyncTask is a simple asynchronous task class provided by Android, which is used to perform time-consuming operations in the background and return the results to the UI thread after the operation is completed. AsyncTask internally uses Handler and Thread to realize the communication between asynchronous operation and UI thread.

When doing multi-threaded programming, you also need to pay attention to the following best practices:

1. Avoid memory leaks: When using multithreading, you need to pay attention to memory leaks. For example, a thread holding a reference to an Activity or Fragment can cause a memory leak. Weak references (WeakReference) can be used to avoid this from happening.

2. Inter-thread communication: Multi-threads need to communicate and cooperate, for example, update UI state from background thread to UI thread. You can use Handler, Messenger, BroadcastReceiver, etc. to achieve communication between threads.

3. Thread synchronization: Thread synchronization is required when multiple threads access shared resources to avoid race conditions and other thread safety issues. You can use the synchronized keyword, Lock and Condition to perform thread synchronization.

Mastering the multi-threaded programming methods and best practices in Android can effectively avoid application interface freezes and ANR errors, and improve application performance and user experience. In the next part, we will give an in-depth introduction to the asynchronous processing technologies in Android, including AsyncTask, Handler, and Looper, etc., to help developers better handle time-consuming operations.

The following are some sample codes showing how to use Thread and HandlerThread for multi-thread programming in Android:

Multithreaded programming using Thread:

new Thread(new Runnable() {<!-- -->
    @Override
    public void run() {<!-- -->
        // perform time-consuming operations in a background thread
        //...
        // Update UI needs to use Handler for UI thread communication
        mHandler. post(new Runnable() {<!-- -->
            @Override
            public void run() {<!-- -->
                // update UI
            }
        });
    }
}).start();

2. Multithreaded programming using HandlerThread:

HandlerThread handlerThread = new HandlerThread("MyHandlerThread");
handlerThread.start();
Handler handler = new Handler(handlerThread. getLooper());

handler. post(new Runnable() {<!-- -->
    @Override
    public void run() {<!-- -->
        // perform time-consuming operations in a background thread
        //...
        // Update UI needs to use Handler for UI thread communication
        mHandler. post(new Runnable() {<!-- -->
            @Override
            public void run() {<!-- -->
                // update UI
            }
        });
    }
});

In summary, multi-threaded programming and asynchronous processing are very important in Android applications, which can improve the responsiveness and performance of the application. Understanding the concept of UI thread and background thread, choosing an appropriate multi-threaded programming method, and following best practices can effectively handle time-consuming operations and avoid application freezes, ANR, and other thread safety issues. The user experience and performance of Android applications can be improved by judicious use of multi-threaded programming and asynchronous processing.

Asynchronous processing in Android

Asynchronous processing is a commonly used programming technique in mobile application development, which is used to perform time-consuming operations in the background, so as not to block the UI thread, and maintain the responsiveness and smoothness of the application. Asynchronous processing can provide a better user experience and avoid ANR (Application Not Responding) errors in the application due to time-consuming operations.

1. Concepts and advantages of asynchronous processing
   Asynchronous processing is a programming style that keeps the UI thread responsive by performing time-consuming operations in a background thread. In mobile applications, common time-consuming operations include network requests, database queries, and file reading and writing. By using asynchronous processing, these time-consuming operations can be put into a background thread for processing, thereby avoiding blocking the UI thread and maintaining application fluency and user experience.

The advantages of asynchronous processing include:

• Provide a better user experience: By performing time-consuming operations in the background and keeping the UI thread responsive, users can continue to interact with the app without feeling stuck or unresponsive.
• Avoid ANR errors: In Android applications, if time-consuming operations are performed in the UI thread for more than a certain time limit, ANR errors will result. This can be avoided by using asynchronous processing.
• Improve application performance: By placing time-consuming operations in background threads, the load on the UI thread can be reduced, thereby improving application performance and response speed.

2. Asynchronous processing in Android
   In Android, a variety of asynchronous processing methods are provided, including but not limited to the following:

• Handler and Looper: Handler and Looper are two key classes in Android for message passing and processing between threads. Handler is used to send messages to the message queue, and Looper is used to process messages in the message queue. By using Handler and Looper in the background thread, time-consuming operations can be put into the message queue, and then the Looper in the UI thread can process these messages, thereby realizing communication and collaboration between the background thread and the UI thread.

// Use Handler and Looper to send messages in the background thread
Handler handler = new Handler(Looper. getMainLooper());
handler. post(new Runnable() {<!-- -->
    @Override
    public void run() {<!-- -->
        // perform time-consuming operation
        //...
    }
});

• AsyncTask: AsyncTask is a built-in asynchronous task class in Android, which encapsulates Handler and Thread, and simplifies the writing of asynchronous operations. By inheriting the AsyncTask class and rewriting the methods in it, you can perform time-consuming operations in a background thread and return the results to the UI thread after the operation is completed.

// Use AsyncTask to perform asynchronous operations
private class MyAsyncTask extends AsyncTask<Void, Void, Void> {<!-- -->
    @Override
    protected Void doInBackground(Void... voids) {<!-- -->
        // perform time-consuming operation
       
//...
return null;
}
@Override
protected void onPostExecute(Void aVoid) {<!-- -->
    super.onPostExecute(aVoid);
    // Process the result of the operation in the UI thread
    //...
}
}

// start asynchronous task
MyAsyncTask myAsyncTask = new MyAsyncTask();
myAsyncTask. execute();

• RxJava: RxJava is a powerful asynchronous processing library that uses the observer pattern and functional programming style to provide a rich set of operators and thread schedulers for processing asynchronous operations and event streams. By using RxJava, asynchronous operations can be processed in a responsive manner, thereby implementing complex asynchronous processing logic.

// Use RxJava to perform asynchronous operations
Observable.fromCallable(new Callable<Void>() {<!-- -->
    @Override
    public Void call() throws Exception {<!-- -->
        // perform time-consuming operation
        //...
        return null;
    }
})
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers. mainThread())
.subscribe(new Observer<Void>() {<!-- -->
    @Override
    public void onSubscribe(Disposable d) {<!-- -->
        // Operations when subscribing
        //...
    }

    @Override
    public void onNext(Void aVoid) {<!-- -->
        // operation when the result is received
        //...
    }

    @Override
    public void onError(Throwable e) {<!-- -->
        // Actions when handling errors
        //...
    }

    @Override
    public void onComplete() {<!-- -->
        // what to do when the operation completes
        //...
    }
});

• Kotlin Coroutines: Kotlin Coroutines is an asynchronous processing method in the Kotlin language. It provides a syntactic sugar that simplifies asynchronous operations, and implements sequential execution of asynchronous operations through coroutines. By using Kotlin Coroutines, you can handle asynchronous operations in your code in a similar way to synchronous code, which simplifies writing asynchronous processing.

// Use Kotlin Coroutines to perform asynchronous operations
suspend fun doAsyncOperation(): Void {<!-- -->
    // perform time-consuming operation
    //...
    return null
}

// Call the asynchronous operation in the coroutine
CoroutineScope(Dispatchers.Main).launch {<!-- -->
    val result = withContext(Dispatchers.IO) {<!-- -->
        doAsyncOperation()
    }
    // process the result in the UI thread
    //...
}

3. Best Practices for Asynchronous Processing
   When using asynchronous processing, you also need to be aware of the following best practices:

• Select the appropriate asynchronous processing method according to the requirements: according to the specific needs and scenarios, select the appropriate asynchronous processing method. For example, for simple asynchronous operations, you can use Handler and Looper; for complex asynchronous operations, you can consider using AsyncTask, RxJava or Kotlin Coroutines, etc.

• Handling exceptions: In asynchronous processing, exceptions may occur, such as network request failures, file read and write errors, etc. Therefore, in asynchronous processing, it is necessary to properly handle exceptions, such as error handling, displaying error prompts, etc., so as to improve application stability and user experience.

• Canceling an asynchronous task: In some cases, it may be necessary to cancel an ongoing asynchronous task, such as when the user cancels the operation or the app is destroyed. Therefore, it is necessary to provide a mechanism to cancel asynchronous tasks. For example, in AsyncTask, you can use the cancel() method to cancel the task. In RxJava, you can use Disposable to cancel the operation. In Kotlin Coroutines Asynchronous operations can be canceled by canceling the coroutine.

// Cancel the task in AsyncTask
MyAsyncTask myAsyncTask = new MyAsyncTask();
myAsyncTask. execute();

// cancel task
myAsyncTask. cancel(true);

// Cancel the task in RxJava
Disposable disposable = Observable. fromCallable(new Callable<Void>() {<!-- -->
    @Override
    public Void call() throws Exception {<!-- -->
        // perform time-consuming operation
        //...
        return null;
    }
})
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers. mainThread())
.subscribe(new Observer<Void>() {<!-- -->
    //...

    @Override
    public void dispose() {<!-- -->
        // cancel task
        disposable. dispose();
    }
});

// Cancel the coroutine in Kotlin Coroutines
val job = CoroutineScope(Dispatchers. Main). launch {<!-- -->
    try {<!-- -->
        // perform time-consuming operation
        //...
    } finally {<!-- -->
        //...
    }
}

// cancel coroutine
job. cancel()

The above is a brief introduction to the concepts, advantages, processing methods and best practices of asynchronous processing in Android. In actual development, according to specific needs and scenarios, choosing an appropriate asynchronous processing method and following best practices can ensure application performance and user experience, and reduce potential errors and exceptions.

Application scenarios of multithreaded programming and asynchronous processing

Multithreaded programming and asynchronous processing are widely used in mobile applications, especially in scenarios that require time-consuming operations or interaction with external resources. Here are some common application scenarios:

1. Network request: Mobile applications often need to make network requests with the server, such as obtaining data, uploading files, and so on. These network requests may take a long time. If they are executed in the UI thread, the application will freeze and the user experience will decrease. Therefore, it is common practice to put network requests on background threads for multi-threaded programming or asynchronous processing.

2. Image loading: Displaying images in mobile applications is a common operation, but image loading may involve time-consuming operations such as downloading from the network, decoding, and scaling. If the picture is loaded in the UI thread, it will cause the interface to freeze. Therefore, using multi-threaded programming or asynchronous processing can ensure that image loading does not affect the performance and user experience of the application.

3. Database operations: Mobile applications often require database operations, such as query, insert, update, etc. Database operations may involve complex queries and a large amount of data processing. If executed in the UI thread, the application will freeze. Therefore, using multi-threaded programming or asynchronous processing can ensure that database operations will not block the UI thread, thereby maintaining the smoothness of the application.

4. Background tasks: There may be some background tasks in the mobile application that need to be executed while the application is running in the background, such as push message processing, data synchronization, and so on. These background tasks may require multi-threaded programming or asynchronous processing in the background thread to ensure that the operation and experience of the foreground user will not be affected when the application is running in the background.

When choosing an appropriate approach to multithreaded programming and asynchronous processing, the following factors need to be considered:

1. Task Complexity: Different tasks may have varying degrees of complexity and time-consuming. For simple tasks, you can choose a lightweight multi-threaded programming method, such as Thread or HandlerThread; for complex tasks, you may need to use a more powerful asynchronous processing framework, such as RxJava or Kotlin Coroutines.

2. Data sharing and synchronization: If multiple threads need to share data or perform data synchronization, thread safety and synchronization mechanisms need to be considered. Some multi-threaded programming methods such as Thread and HandlerThread require developers to manually handle thread synchronization and data sharing, while some asynchronous processing frameworks such as RxJava and Kotlin Coroutines provide convenient thread safety and data synchronization mechanisms.

3. UI interaction: If the task involves UI interaction, such as updating the UI interface or handling UI events, it needs to be considered to execute in the UI thread, or use the method of communicating with the UI thread for multi-threaded programming or asynchronous processing.

4. Code readability and maintainability: When choosing the appropriate multi-threaded programming and asynchronous processing methods, you also need to consider the readability and maintainability of the code. Some multi-threaded programming methods may make the code complex and difficult to maintain, while some asynchronous processing frameworks provide concise syntax and abstraction, making the code clearer and easier to maintain.

The following are some sample codes showing examples of choosing the appropriate multi-threaded programming and asynchronous processing methods in different scenarios:

1. Asynchronous processing using Handler and MessageQueue:

// Create a Handler in the UI thread
Handler handler = new Handler();

// perform time-consuming operations in a background thread
new Thread(new Runnable() {<!-- -->
    @Override
    public void run() {<!-- -->
        // perform time-consuming operation
        //...

        // Send the result to the UI thread
        handler. post(new Runnable() {<!-- -->
            @Override
            public void run() {<!-- -->
                // Update the UI interface
                //...
            }
        });
    }
}).start();

2. Use AsyncTask for asynchronous processing:

// create AsyncTask
private class MyAsyncTask extends AsyncTask<Void, Void, Void> {<!-- -->
    @Override
    protected Void doInBackground(Void... voids) {<!-- -->
        // perform time-consuming operation
        //...
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {<!-- -->
        super.onPostExecute(aVoid);
        // Update the UI interface
        //...
    }
}

// Execute AsyncTask in the UI thread
MyAsyncTask myAsyncTask = new MyAsyncTask();
myAsyncTask. execute();

3. Asynchronous processing with RxJava:

// create Observable
Observable.create(new ObservableOnSubscribe<Void>() {<!-- -->
    @Override
    public void subscribe(ObservableEmitter<Void> emitter) throws Exception {<!-- -->
        // perform time-consuming operation
        //...
        emitter.onComplete();
    }
})
.subscribeOn(Schedulers.io()) // Specify to execute in the IO thread
.observeOn(AndroidSchedulers.mainThread()) // Specify to observe the results in the UI thread
.subscribe(new Observer<Void>() {<!-- -->
    @Override
    public void onSubscribe(Disposable d) {<!-- -->
        // optional subscription operation
    }

    @Override
    public void onNext(Void aVoid) {<!-- -->
        // No processing is required because no data is emitted
    }

    @Override
    public void onError(Throwable e) {<!-- -->
        // handle exception
    }

    @Override
    public void onComplete() {<!-- -->
        // Update the UI interface
        //...
    }
});

4. Asynchronous processing with Kotlin Coroutines:

// Perform time-consuming operations in the IO thread
GlobalScope.launch(Dispatchers.IO) {<!-- -->
    // perform time-consuming operation
    //...

    // Switch back to the UI thread to update the UI interface
    withContext(Dispatchers. Main) {<!-- -->
        // Update the UI interface
        //...
    }
}

The above sample code shows some examples of choosing appropriate multi-threaded programming and asynchronous processing methods in different scenarios. In practical applications, developers need to comprehensively consider factors such as task complexity, data sharing and synchronization, UI interaction, code readability and maintainability according to specific needs and scenarios.

Conclusion

In modern Android application development, multi-thread programming and asynchronous processing are important technologies that cannot be ignored. Judicious use of multithreading and asynchronous processing can improve the performance and user experience of your application, ensure that your application remains responsive while performing time-consuming operations, and avoid ANR (Application Not Responding) errors. In this section, we summarize multithreaded programming and asynchronous processing, and provide some best practices and considerations.

First of all, the importance of multithreaded programming and asynchronous processing in Android applications is self-evident. Time-consuming operations, such as network requests, database operations, image loading, etc., should be executed in the background thread to avoid blocking the UI thread, so as to maintain the smoothness and responsiveness of the application. At the same time, asynchronous processing can also be used to execute multiple independent tasks concurrently, thereby improving the processing capability and efficiency of the application.

Here are some best practices and considerations when doing multithreaded programming and asynchronous processing:

1. Use appropriate multi-threaded programming and asynchronous processing methods: According to the complexity of tasks, data sharing and synchronization, UI interaction and other factors, choose appropriate multi-threaded programming and asynchronous processing methods, such as Handler and MessageQueue, AsyncTask, RxJava, Kotlin Coroutines, etc. .

2. Avoid performing time-consuming operations in the UI thread: Place time-consuming operations in the background thread to avoid blocking the UI thread and causing the application to become unresponsive.

3. Manage threads and tasks reasonably: avoid creating too many threads and tasks, manage thread pools reasonably, and avoid thread leakage and resource waste.

4. Handle inter-thread communication and data sharing: Use appropriate inter-thread communication methods, such as Handler, BroadcastReceiver, LocalBroadcastManager, etc., to ensure the correctness of inter-thread data sharing and synchronization.

5. Handling exceptions and errors: In multi-threaded programming and asynchronous processing, exceptions and errors need to be handled in a timely manner to ensure application stability and reliability.

6. Consider the readability and maintainability of the code: When choosing an appropriate multi-threaded programming and asynchronous processing method, consider the readability and maintainability of the code, and choose concise and clear syntax and abstraction to facilitate subsequent maintenance and expansion.

In summary, multithreaded programming and asynchronous processing play an important role in modern Android application development. Judicious use of multithreading and asynchronous processing can improve your app’s performance and user experience, and ensure that your app remains responsive when performing time-consuming operations. By following the best practices and precautions, developers can write efficient, stable, readable and maintainable multi-threaded and asynchronous processing code, thereby improving the quality and stability of the application. Multi-thread programming and asynchronous processing are indispensable technologies in Android application development. Developers should apply them reasonably in applications and follow related best practices and precautions.

In conclusion, we want to emphasize the importance of multithreaded programming and asynchronous processing for modern Android applications. They help apps stay responsive while processing time-consuming operations, improve user experience, and ensure app stability and reliability. Reasonable selection and use of multi-threaded programming and asynchronous processing methods, as well as following best practices and precautions, will help to develop efficient, stable and maintainable Android applications.

When performing multi-threaded programming and asynchronous processing, developers should have a deep understanding of the relevant APIs and mechanisms of the Android platform, understand the advantages and disadvantages of different methods, and make appropriate choices according to application requirements and scenarios. At the same time, pay attention to the communication and data sharing between threads to avoid thread safety issues and waste of resources. When handling exceptions and errors, it is necessary to capture and process them in time to ensure the stability of the application. In addition, developers should also pay attention to the readability and maintainability of the code, and choose the appropriate syntax and abstraction to facilitate subsequent maintenance and expansion.

In general, multi-thread programming and asynchronous processing are indispensable technologies in the development of modern Android applications. Reasonable application of them will help improve application performance, user experience and stability. By following the best practices and precautions, developers can write efficient, stable, and maintainable multi-threaded and asynchronous processing code, so as to build better Android applications.