By default, ANTLR 4 generates listeners. But if you give org.antlr.v4.Tool the command line parameter -visitor, ANTLR generates visitor classes for you. These work much like listeners, but give you more control over which (sub) trees are walked/visited. This is particularly useful if you want to exclude certain (sub) trees (like else/if blocks, as in … Read more
You will learn the way to do it, in an easy way, is: public class Mtest extends Activity { Button b1; Button b2; public void onCreate(Bundle savedInstanceState) { … b1 = (Button) findViewById(R.id.b1); b2 = (Button) findViewById(R.id.b2); b1.setOnClickListener(myhandler1); b2.setOnClickListener(myhandler2); … } View.OnClickListener myhandler1 = new View.OnClickListener() { public void onClick(View v) { // it was … Read more
You probably want to look into the observer pattern. Here’s some sample code to get yourself started: import java.util.*; // An interface to be implemented by everyone interested in “Hello” events interface HelloListener { void someoneSaidHello(); } // Someone who says “Hello” class Initiater { private List<HelloListener> listeners = new ArrayList<HelloListener>(); public void addListener(HelloListener toAdd) … Read more
In the example below, the TableModel updates a Set<Integer> checked in the implementation of setValueAt(). The model of an adjacent JList listens to the table’s model and displays the currently selected row numbers. The example assumes that the number of selected rows is small compared to the number of rows. Note the use of TreeSet, … Read more
Every instance of View calls getViewTreeObserver(). Now when holding an instance of ViewTreeObserver, you can add an OnScrollChangedListener() to it using the method addOnScrollChangedListener(). You can see more information about this class here. It lets you be aware of every scrolling event – but without the coordinates. You can get them by using getScrollY() or … Read more
I’ve written a log file monitor before, and I found that the impact on system performance of polling the attributes of a single file, a few times a second, is actually very small. Java 7, as part of NIO.2 has added the WatchService API The WatchService API is designed for applications that need to be … Read more
In modern browsers, you can use the let or const keywords to create a block-scoped variable: for (let i = 0; i < results.length; i++) { let marker = results[i]; google.maps.event.addListener(marker, ‘click’, () => change_selection(i)); } In older browsers, you need to create a separate scope that saves the variable in its current state by … Read more
Add a listener to the underlying Document, which is automatically created for you. // Listen for changes in the text textField.getDocument().addDocumentListener(new DocumentListener() { public void changedUpdate(DocumentEvent e) { warn(); } public void removeUpdate(DocumentEvent e) { warn(); } public void insertUpdate(DocumentEvent e) { warn(); } public void warn() { if (Integer.parseInt(textField.getText())<=0){ JOptionPane.showMessageDialog(null, “Error: Please enter number … Read more
The valueChangeListener will only be invoked when the form is submitted and the submitted value is different from the initial value. It’s thus not invoked when only the HTML DOM change event is fired. If you would like to submit the form during the HTML DOM change event, then you’d need to add another <f:ajax/> … Read more
You need to use named functions. Also, the click variable needs to be outside the handler to increment. var click_count = 0; function myClick(event) { click_count++; if(click_count == 50) { // to remove canvas.removeEventListener(‘click’, myClick); } } // to add canvas.addEventListener(‘click’, myClick); EDIT: You could close around the click_counter variable like this: var myClick = … Read more