Desactivate alert dialog positive button on empty string input

Question

I want to enable an alertDialog positive button only when user input is not empty and disable it if user input is empty, a king of toggling for validation purpose, user input must not be empty. here is my code, even if I put a string the button does not activate.

buildInfos.setPositiveButton(android.R.string.ok, new OnClickListener() {

    @Override
    public void onClick(DialogInterface dialog, int which) {
        infosDesc = inputInfos.getText().toString();
        Log.i("DESC", infosDesc);
        drawBetween2LastPoints(getAlertColor(alertType), "title", infosDesc);
    }
});

AlertDialog buildInfosDialog = buildInfos.create();
buildInfosDialog.show();
if(infosDesc.isEmpty()){
    buildInfosDialog.getButton(Dialog.BUTTON_POSITIVE).setEnabled(false);
}

Answer 1

In your code above, you only check if the field is empty right after you show the dialog. You'll have to watch the EditTexts content for change. For this purpose, you can add a TextWatcher to the field, by using it's addTextChangedListener(TextWatcher)-method.

In the TextWatcher, overwrite the afterTextChanged(Editable)-method, which is called every time the contents of the field change (something was added/removed). In it, check if there is anything in the EditText. If there is, activate the button. If not, deactivate it.

Here is an example Implementation:

public class Main extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Button button = new Button(this);
        button.setText("Show Dialog");
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showDialog();
            }
        });

        setContentView(button);
    }

    private void showDialog(){
        // Create the field to show in the Dialog:
        final EditText field = new EditText(this);

        // Now create the Dialog itself.
        final AlertDialog dialog = new AlertDialog.Builder(this)
                .setMessage("Enter something")
                .setPositiveButton("O.K.", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        Toast.makeText(Main.this, "Submitted with \""+field.getText().toString()+"\"",
                                Toast.LENGTH_LONG).show();
                    }
                }).setCancelable(true).setView(field)
                .create();

        // The TextWatcher will look for changes to the Dialogs field.
        field.addTextChangedListener(new TextWatcher() {
            @Override public void beforeTextChanged(CharSequence c, int i, int i2, int i3) {}
            @Override public void onTextChanged(CharSequence c, int i, int i2, int i3) {}

            @Override
            public void afterTextChanged(Editable editable) {
                // Will be called AFTER text has been changed.
                if (editable.toString().length() == 0){
                    dialog.getButton(AlertDialog.BUTTON_POSITIVE).setEnabled(false);
                } else {
                    dialog.getButton(AlertDialog.BUTTON_POSITIVE).setEnabled(true);
                }
            }
        });

        // Show the Dialog:
        dialog.show();
        // The button is initially deactivated, as the field is initially empty:
        dialog.getButton(AlertDialog.BUTTON_POSITIVE).setEnabled(false);
    }
}