无法在未调用Looper.prepare（）的线程内创建处理程序-Android Marmalade

Question

I'm trying to add USB controller support to my Android game. I'm using Marmalade and I've created an extension based on the USB example code. Here it is:

public class GameControllerInput extends Activity
             implements InputManager.InputDeviceListener 
{
    private static final String TAG = "GameControllerInput";

    private InputManager mInputManager;
    private SparseArray<InputDeviceState> mInputDeviceStates;

    private static int numEvents = 0;


    public int EDK_GameControllerInput_Init()
    {
        LoaderActivity.m_Activity.runOnUiThread(new Runnable() 
        {
        public void run()
        {
            Log.i(TAG, "Running 1 =========================");
        }
    });
    Log.i(TAG, "Init 2 =========================");
    return 1;

When I call the init function I get this error:

java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

I've read other threads with this error and they say the solution is to add the LoaderActivity.m_Activity.runOnUiThread(new Runnable() code. However, as you can see, adding this just gives me the same error.

I'm not experienced with Java and I'm at a loss on how to fix this. Any help would be greatly appreciated.

Cheers, Steve

Answer 1

A Looper (a message queue processor) is tied to a single thread, each thread has at most one looper. A Handler needs to register itself with a Looper to work, so each time you invoke new Handler() , it tries to get the Looper for the current thread (the thread that's creating the Handler ), which can be either present or not. The exception that you see is thrown because the thread that's creating the handler does not have a looper.

There is one two things that you can do to fix this:

• Add a Looper to the current thread.
• Make sure you're creating the Handler on a thread that already has a Looper .

In almost all cases, the handler is used to communicate from a background thread to the UI thread, I'm assuming that's the case here. That means option 2. Your runOnUiThread(Runnable) thing is close, but no cigar, because all it does is write to the log file.

You need to move the code that creates the new Handler() (not shown in your posted code sample) into the runOnUiThread block, or use some other way to get it to run on the UI thread. The typical way to do this is to create it in the onCreate(Bundle) method of your activity or fragment.

Keep in mind that, depending on your initialization order, this may mean it's initially null as seen by your background thread, so the background code will have to be able to deal with that.

Answer 2

最好有一个回调方法，仅在s4e文件中的方法声明之后调用run_on_os_thread ，将其标记为主线程。