Android: wait on user input from dialog?

Solution 1:

Is this possible?

No. There is no blocking UI model in Android. Everything is asynchronous.

UPDATE

In response to some of your comments on the question itself, you cannot display a UI from a background thread. As I wrote in this answer, there is no blocking UI model in Android. Just put your code in the button handler for your dialog that you want to have executed when the dialog is accepted, such as in this sample project.

Solution 2:

The right way to do this is an event driven program model, ie, "don't call us, we'll call you".

In simple console mode programming, your code tends to call blocking input functions, which don't return until you've gotten a value.

Many gui programming environments work differently - your code is not normally running, but instead it's called by the operating system / window manager when something of potential interest happens. You do something in response to this and promptly return - if you do not, you can't be notified of anything else since the OS has no way to contact you until you return. (In comparison to win32, it's as if the message loop is implemented by Android, and you only get to write the rest of the code that the message loop calls with events - if you don't return promptly, the message loop hangs)

As a result, you need to rethink your concept of program flow. Instead of writing out a to-do list as a simple series of statements, think about it as a sequence of actions which depend on each other and on input. Remember what action you are currently on in a state variable. When you get called with an event such as user input, see if that event means it's now possible to move on to the next step, and if so update your state variable before promptly returning to the OS in order to be able to receive the next event. If the event wasn't what you needed, then just return without updating your state.

If this model won't work for you, what you can do is write a background thread of program logic which runs like a console-mode application using blocking input. But your input functions will really just wait on a flag or something to be notified that input is available. Then on your UI thread where Android delivers events, you update the flag and promptly return. The background thread sees the flag has changed to indicate that data has been provided, and continues execution. (Something like an android terminal emulator takes this to an extreme, where the background component is actually another process - a console mode linux one, and it gets its input using potentially blocking I/O from pipes. The java component accepts android UI events and stuffs characters into the stdin pipe and pulls them out of the stdout pipe to display on the screen.)

Solution 3:

Thanks for all the feedback, I was able to solve this using a background thread along with a wait() and notify(). I recognize this isn't the greatest idea for the given paradigm, but it was necessary to conform to a library that I am working with.

Solution 4:

I had a hard time understanding all the solutions offered above so far so I found my own one.

I wrap the code thats supposed to be performed after the user input is OK'ed in a runnable, like so:

    Runnable rOpenFile = new Runnable() {
        @Override
        public void run() {
            .... code to perform
        }
    }

Then right below that I pass the name of the runnable function to the user dialog method.

    userInput("Open File", rOpenFile);

The userInput method is based on the alertDialog builder like described above. When the user input is Ok'ed it starts the intended runnable.

private void userInput(String sTitle, final Runnable func) {
    AlertDialog.Builder aBuilder = new AlertDialog.Builder(this);

    aBuilder.setTitle(sTitle);
    final EditText input = new EditText(this);
    input.setInputType(InputType.TYPE_CLASS_TEXT);
    aBuilder.setView(input);

    bDialogDone = false;

    aBuilder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            final String sText = input.getText().toString();
            sEingabe = sText;
            func.run();
        }
    });
    aBuilder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
            sEingabe = "";
        }
    });

    aBuilder.show();
}