Reza

Thread

2 min read

Problem Description

The error encountered is:

java.lang.RuntimeException: Unable to start activity ComponentInfo{ir.rezajax.newproxyserver/ir.rezajax.newproxyserver.MainActivity}: android.os.NetworkOnMainThreadException

This indicates that a network operation (such as ServerSocket.accept) was performed on the Main Thread, which is not allowed on Android due to potential UI freezing and poor user experience.

Cause of the Issue

On Android, long-running or blocking operations (e.g., networking, heavy file I/O, or database operations) cannot be executed on the Main Thread. Android enforces this through **StrictMode**, which throws a NetworkOnMainThreadException when such code is run on the main thread.

Solution

You must move network operations, like ServerSocket.accept(), to a separate thread or a background task. Below are some ways to handle this:

Fix Using a Thread

Move the network operation to a new thread:

Thread {
    try {
        val serverSocket = ServerSocket(1122)
        while (true) {
            val socket = serverSocket.accept()
            // Process incoming data
        }
    } catch (e: Exception) {
        e.printStackTrace()
    }
}.start()

Fix Using Kotlin Coroutines

If you’re using Kotlin Coroutines:

import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext

GlobalScope.launch(Dispatchers.IO) {
    try {
        val serverSocket = ServerSocket(1122)
        while (true) {
            val socket = serverSocket.accept()
            // Process incoming data
        }
    } catch (e: Exception) {
        e.printStackTrace()
    }
}

Key Points

  • Use **Dispatchers.IO** for I/O-bound operations like networking.

  • Avoid using **GlobalScope** indiscriminately. Instead, use lifecycle-aware coroutines if your app structure allows it (e.g., with ViewModel or CoroutineScope).

Additional Debugging

If the problem persists, carefully inspect the line of code where the issue originates, specifically MainActivity.kt line 50 as mentioned in the logs. The offending code must be offloaded to a background thread or coroutine.

References

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