Android's Activity.runOnUiThread is not static

Question

For example, if I have a thread doing expensive stuff, and from that thread I want to fire runOnUiThread in the Main (activity) class. Obviously I shouldn't make an instance of my activity class (Main). So if I try

 Main.runOnUiThread(mRunnable);

from my thread it gives me an error saying it's not a static method, and therefor it can't be accessed in my way. Now my understanding would be that the activity class is nearly almost accessed in a static way.
How would I do this?

(Btw: I'm doing this because I was getting CalledFromWrongThreadException, Only the original thread that created a view hierarchy can touch it's views)

Answer 1

all of the above answers are not very correct.

1)if you want a piece of code to run on UI thread from any thread code base. you can do: Looper.getMainLooper().post(new Runnable(...))

because Looper.getMainLooper() is a static variable and initialized in ActivityThread.

2) if your runnable code snippet is inside an activity then you can use:

MainActivity.this.runOnUiThread(...)

Answer 2

Raunak has the right idea. I'll just add that you can also specify an integer in the method sendEmptyMessage as an identifier to the handler. This will allow you to create one handler that can handle all of your UI updates, e.g.

public static final int EXAMPLE = 0;
public static final int ANOTHER_EXAMPLE = 1;

private final Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        switch( msg.what ){
            case EXAMPLE: 
                //Perform action
                break;
            case ANOTHER_EXAMPLE;
                //Perform action
                break;
        }
    }
} 

//Call to submit handler requesting the first action be called
handler.sendEmptyMessage(EXAMPLE);

Hope this helps!

Answer 3

Your question doesn't really provide enough details, but from the sound of things, you're in a private inner class (Runnable?) in your activity (Main). If that is the case, you can either write:

Main.this.runOnUiThread(mRunnable);

or

runOnUiThread(mRunnable); //will see that there is no runOnUiThread in the current class and begin looking "upwards"

Also, you may want to look at AsyncTask, specifically at the onPostExecute, onPreExecute and onProgressUpdate callbacks, which run on the UI thread.

Answer 4

first create a runnable outside onCreate. Like this:

private Runnable myRunnable = new Runnable() {
        @Override
        public void run() {

                        //work to be done

        }
    };

and then call the runnable using:

runOnUiThread(myRunnable);

Answer 5

For those who are looking for an easy instant solution follow the simple steps

• Make a reference of your class before your onCreate() method

  MyClass obj;
  

• Initialize it in you onCreate() method

  obj = MyClass.this;
  

• Call runOnUiThread()

  obj.runOnUiThread(new Runnable() {
      public void run() {
      //perform your UI tasks here
      }
  });
  

Hope it helps.

Answer 6

You should use the Handler class. The handler class runs on the UI thread. When you finish work in your thread, call handler.sendEmptyMessage(), from where you can make the changes to your ui.

private final Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
         // make changes to ui
    }
}