Home/ Questions/Q 8889917
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-14T22:22:51+00:00

I am a newbie in Android and creating a mini FTP download manager for

  • 0

I am a newbie in Android and creating a mini FTP download manager for myself.. I am using multithreading, each thread to handle one download or upload. In the MainActivity.java, I am using two spinners in the view. One to list the files on the server (which can be downloaded), another to list files on my phone folder (which can be uploaded). I want to update the first (download) spinner when a new file is uploaded, and the second (upload) spinner when a new file is downloaded. However I am not able to make out how to update the spinners only when the corresponding threads finish their job. I created methods to update the spinners in the MainActivity.java and tried to call them in the end of the run() of the threads, so that they’l be updated once the threads finish downloading/uploading. However, I am getting an error in LogCat saying

android.view.ViewRoot$CalledFromWrongThreadException : Only the original thread that created a view hierarchy can touch its views.

The method for updating upload spinner is: 

void upScrollUpdate() {
    spinup=(Spinner)findViewById(R.id.uploadspin);
    spinup.setEnabled(false);
    String[] upload={"No Files"};
    File sdDir=Environment.getExternalStorageDirectory();
    File dir=new File (sdDir.getAbsolutePath() + "/aFTP");
    File[] fArray=dir.listFiles();
    if(fArray.length>0) {
        upload=new String[fArray.length];
    }
    for(int i=0;i<fArray.length;i++) {
        upload[i]=fArray[i].getName();
    }
    ArrayAdapter<String> saaUpload=new ArrayAdapter<String>(this,android.R.layout.simple_spinner_dropdown_item,upload);
    spinup.setAdapter(saaUpload);
    if(spinup.getSelectedItem().toString().equalsIgnoreCase("No Files")) {
        uploadButton.setEnabled(false);
    }
    spinup.setEnabled(true);
}

Why cant this method be called from another thread, and what is the other way out of this, I simply want to update the spinners but I have spent a whole day on this only thing…

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    For any piece of code that will update the UI, put that in this block:

    Refer to this link for more info on runOnUiThread

    runOnUiThread(new Runnable() {
     public void run() {

         // RUN THE CODE WHICH IS GIVING THAT EXCEPTION HERE

    }
});

    The same can also be done like this:

    Runnable run = new Runnable() {

    @Override
    public void run() {

        // RUN THE CODE WHICH IS GIVING THAT EXCEPTION HERE

    }
}; YourActivity.this.runOnUiThread(run);

    Alternatively, you can make use of an AsyncTask. You can do your processing in the doInBackground() method and then update the Spinners in the onPostExecute() method of the AsyncTask

    EDIT: Check these tutorials to help you get started with using AsyncTask:

    1. http://www.vogella.com/articles/AndroidPerformance/article.html#asynctask
    2. http://androidresearch.wordpress.com/2012/03/17/understanding-asynctask-once-and-forever/
    3. http://android10.org/index.php/articlesother/239-android-application-and-asynctask-basics
    4. http://mobileorchard.com/android-app-developmentthreading-part-2-async-tasks/
    5. http://thenewboston.org/watch.php?cat=6&number=101

    The 5th link to thenewboston.org has about 200 odd video tutorials on YouTube here: http://www.youtube.com/course?list=EC2F07DBCDCC01493A&feature=plcp

    EDIT 2: Check the edit in this link here: https://stackoverflow.com/a/13265776/450534

    It is at the bottom of the answer.

    • 0