How to check if current thread is not main thread

Question

I need to check if the thread running a certain piece of code is the main (UI) thread or not. How can I achieve this?

Answer 1

Looper.myLooper() == Looper.getMainLooper()

if this returns true, then you're on the UI thread!

Answer 2

you can use below code to know if current thread is UI/Main thread or not

if(Looper.myLooper() == Looper.getMainLooper()) {
   // Current Thread is Main Thread.
}

or you can also use this

if(Looper.getMainLooper().getThread() == Thread.currentThread()) {
   // Current Thread is Main Thread.
}

Here is similar question

Answer 3

The best way is the clearest, most robust way: *

Thread.currentThread().equals( Looper.getMainLooper().getThread() )

Or, if the runtime platform is API level 23 (Marshmallow 6.0) or higher:

Looper.getMainLooper().isCurrentThread()

See the Looper API. Note that calling Looper.getMainLooper() involves synchronization (see the source). You might want to avoid the overhead by storing the return value and reusing it.

   * credit greg7gkb and 2cupsOfTech

Answer 4

Summarizing the solutions, I think that's the best one:

boolean isUiThread = VERSION.SDK_INT >= VERSION_CODES.M 
    ? Looper.getMainLooper().isCurrentThread()
    : Thread.currentThread() == Looper.getMainLooper().getThread();

And, if you wish to run something on the UI thread, you can use this:

new Handler(Looper.getMainLooper()).post(new Runnable() {
    @Override
    public void run() {
       //this runs on the UI thread
    }
});

Answer 5

You can check

if(Looper.myLooper() == Looper.getMainLooper()) {
   // You are on mainThread 
}else{
// you are on non-ui thread
}

Answer 6

Allow me to preface this with: I acknowledged this post has the 'Android' tag, however, my search had nothing to do with 'Android' and this was my top result. To that end, for the non-Android SO Java users landing here, don't forget about:

public static void main(String[] args{
    Thread.currentThread().setName("SomeNameIChoose");
    /*...the rest of main...*/
}

After setting this, elsewhere in your code, you can easily check if you're about to execute on the main thread with:

if(Thread.currentThread().getName().equals("SomeNameIChoose"))
{
    //do something on main thread
}

A bit embarrassed I had searched before remembering this, but hopefully it will help someone else!

Answer 7

First of all check It is main Thread or not

In Kotlin

fun isRunningOnMainThread(): Boolean {
    return Thread.currentThread() == Looper.getMainLooper().thread
}

In Java

static boolean isRunningOnMainThread() {
  return Thread.currentThread().equals(Looper.getMainLooper().getThread());
}

Answer 8

just log this line, it should print "main".

Thread.currentThread().name

Answer 9

In addition to all previous answers

inline fun <T> ensureNotOnMainThread(block: () -> T): T {
    check(Thread.currentThread() != Looper.getMainLooper().thread) { "This function cannot be called on main thread" }
    return block()
}

allows to wrap any method with it, following example :

fun isInDataBase(id: String) = ensureNotOnMainThread { db.contains(id) }

Answer 10

you can verify it in android ddms logcat where process id will be same but thread id will be different.

Answer 11

Xamarin.Android port: (C#)

public bool IsMainThread => Build.VERSION.SdkInt >= BuildVersionCodes.M
    ? Looper.MainLooper.IsCurrentThread
    : Looper.MyLooper() == Looper.MainLooper;

Usage:

if (IsMainThread) {
    // you are on UI/Main thread
}

Answer 12

So another answer to join the company, for some extension file in kotlin:

import android.os.Looper.getMainLooper
import java.lang.Thread.currentThread

val Thread.isMain get() = getMainLooper().thread == this

val isThreadMain get() = getMainLooper().thread == currentThread()

Answer 13

A simple Toast message works also as a quick check.

Answer 14

A coroutines-based, Android-agnostic approach:

val onMainThread: Boolean
    get() = Thread.currentThread() === try {
        runBlocking(Dispatchers.Main.immediate) {
            Thread.currentThread()
        }
    } catch (e: IllegalStateException) {
        // No main dispatcher has been registered; not in an Android context?
        null
    }

Answer 15

You can try Thread.currentThread().isDaemon()