仅在线程终止后才显示进度对话框

Question

I'm trying to connect to a TCP/IP socket in a thread the moment my app is opened, and would like to show a progress dialog while connecting. The problem is that the thread is always executed before the progress dialog is shown, which means that it is shown only after the socket connection has actually happened (or failed).

public static boolean startConnection (Context c) {

    boolean[] ret = new boolean[1];

    ProgressDialog progressDialog = new ProgressDialog(c);
    progressDialog.setMessage("Connecting...");
    progressDialog.show();

    Thread t = new Thread() {
        @Override
        public void run() {
            try {
                clientSocket = new Socket();
                clientSocket.connect(new InetSocketAddress(SERVER_IP, SERVER_PORT), 5000);
                ret[0] = true;
            }
            catch (IOException e) {
                e.printStackTrace();
                ret[0] = false;
            }
            ((Activity)c).runOnUiThread(progressDialog::dismiss);
        }
    };

    t.start();
    try {
        t.join();
    } 
    catch (InterruptedException e) {
        e.printStackTrace();
    }

    return ret[0];

}

And I'm invoking startConnection in the onStart() method:

protected void onStart() {

    super.onStart();
    if (ConnectionHandler.startConnection(this)) {
        goToMainActivity();
    }
    else {
        Toast.makeText(this, "Connection error.", Toast.LENGTH_LONG).show();
    }

}
   

How can I make it so that the progress dialog is shown before the thread actually starts?

Answer 1

t.join(); waits on the UI main thread until second thread t finishes, that's the reason your code is blocking the UI thread and the dialog doesn't appear.

In addition you can't call progressDialog.dismiss() ; on the t thread, all code that interacts with the UI must be called on the main thread, you can try tom call it using runOnUIThread() activity method