TextField
TextField is one of the most commonly used user interface components. It is a Field component that allows entering textual values with keyboard.
The following example creates a simple text field:
// Create a text field
TextField tf = new TextField("A Field");
// Put some initial content in it
tf.setValue("Stuff in the field");See the on-line example.
The result is shown in TextField Example.
Value changes are handled with a Property.ValueChangeListener, as in most other fields. The value can be acquired with getValue() directly from the text field, as is done in the example below, or from the property reference of the event.
// Handle changes in the value
tf.addValueChangeListener(new Property.ValueChangeListener() {
public void valueChange(ValueChangeEvent event) {
// Assuming that the value type is a String
String value = (String) event.getProperty().getValue();
// Do something with the value
Notification.show("Value is: " + value);
}
});
// Fire value changes immediately when the field loses focus
tf.setImmediate(true);See the on-line example.
As with other event listeners, you can use lambda expression with one parameter to handle the events in Java 8.
Much of the API of TextField is defined in AbstractTextField, which allows different kinds of text input fields, such as rich text editors, which do not share all the features of the single-line text fields.
Data Binding
TextField edits String values, but you can bind it to any property type that has a proper converter, as described in "Converting Between Property Type and Representation".
// Have an initial data model. As Double is unmodificable and
// doesn't support assignment from String, the object is
// reconstructed in the wrapper when the value is changed.
Double trouble = 42.0;
// Wrap it in a property data source
final ObjectProperty<Double> property =
new ObjectProperty<Double>(trouble);
// Create a text field bound to it
// (StringToDoubleConverter is used automatically)
TextField tf = new TextField("The Answer", property);
tf.setImmediate(true);
// Show that the value is really written back to the
// data source when edited by user.
Label feedback = new Label(property);
feedback.setCaption("The Value");See the on-line example.
When you put a Table in editable mode or create fields with a FieldGroup, the DefaultFieldFactory creates a TextField for almost every property type by default. You often need to make a custom factory to customize the creation and to set the field tooltip, validation, formatting, and so on.
See "Binding Components to Data" for more details on data binding, field factories for Table in "Editing the Values in a Table", and "Creating Forms by Binding Fields to Items" regarding forms.
String Length
The setMaxLength() method sets the maximum length of the input string so that the browser prevents the user from entering a longer one. As a security feature, the input value is automatically truncated on the server-side, as the maximum length setting could be bypassed on the client-side. The maximum length property is defined at AbstractTextField level.
Notice that the maximum length setting does not affect the width of the field. You can set the width with setWidth(), as with other components. Using em widths is recommended to better approximate the proper width in relation to the size of the used font, but the em width is not exactly the width of a letter and varies by browser and operating system. There is no standard way in HTML for setting the width exactly to a number of letters (in a monospaced font).
Handling Null Values
As with any field, the value of a TextField can be set as null. This occurs most commonly when you create a new field without setting a value for it or bind the field value to a data source that allows null values. In such case, you might want to show a special value that stands for the null value. You can set the null representation with the setNullRepresentation() method. Most typically, you use an empty string for the null representation, unless you want to differentiate from a string that is explicitly empty. The default null representation is "null", which essentially warns that you may have forgotten to initialize your data objects properly.
The setNullSettingAllowed() controls whether the user can actually input a null value by using the null value representation. If the setting is false, which is the default, inputting the null value representation string sets the value as the literal value of the string, not null. This default assumption is a safeguard for data sources that may not allow null values.
// Have a property with null value
ObjectProperty<Double> dataModel =
new ObjectProperty<Double>(new Double(0.0));
dataModel.setValue(null); // Have to set it null here
// Create a text field bound to the null data
TextField tf = new TextField("Field Energy (J)", dataModel);
tf.setNullRepresentation("-- null-point --");
// Allow user to input the null value by its representation
tf.setNullSettingAllowed(true);See the on-line example.
The Label, which is bound to the value of the TextField, displays a null value as empty. The resulting user interface is shown in Null Value Representation.
Text Change Events
Often you want to receive a change event immediately when the text field value changes. The immediate mode is not literally immediate, as the changes are transmitted only after the field loses focus. In the other extreme, using keyboard events for every keypress would make typing unbearably slow and also processing the keypresses is too complicated for most purposes. Text change events are transmitted asynchronously soon after typing and do not block typing while an event is being processed.
Text change events are received with a TextChangeListener, as is done in the following example that demonstrates how to create a text length counter:
// Text field with maximum length
final TextField tf = new TextField("My Eventful Field");
tf.setValue("Initial content");
tf.setMaxLength(20);
// Counter for input length
final Label counter = new Label();
counter.setValue(tf.getValue().length() +
" of " + tf.getMaxLength());
// Display the current length interactively in the counter
tf.addTextChangeListener(new TextChangeListener() {
public void textChange(TextChangeEvent event) {
int len = event.getText().length();
counter.setValue(len + " of " + tf.getMaxLength());
}
});
// The lazy mode is actually the default
tf.setTextChangeEventMode(TextChangeEventMode.LAZY);See the on-line example.
The result is shown in Text Change Events.
The text change event mode defines how quickly the changes are transmitted to the server and cause a server-side event. Lazier change events allow sending larger changes in one event if the user is typing fast, thereby reducing server requests.
You can set the text change event mode of a TextField with setTextChangeEventMode(). The allowed modes are defined in TextChangeEventMode enum and are as follows:
- TextChangeEventMode.LAZY(default)
-
An event is triggered when there is a pause in editing the text. The length of the pause can be modified with setInputEventTimeout(). As with the TIMEOUT mode, a text change event is forced before a possible ValueChangeEvent, even if the user did not keep a pause while entering the text.
This is the default mode.
- TextChangeEventMode.TIMEOUT
-
A text change in the user interface causes the event to be communicated to the application after a timeout period. If more changes are made during this period, the event sent to the server-side includes the changes made up to the last change. The length of the timeout can be set with setInputEventTimeout().
If a ValueChangeEvent would occur before the timeout period, a TextChangeEvent is triggered before it, on the condition that the text content has changed since the previous TextChangeEvent.
- TextChangeEventMode.EAGER
-
An event is triggered immediately for every change in the text content, typically caused by a key press. The requests are separate and are processed sequentially one after another. Change events are nevertheless communicated asynchronously to the server, so further input can be typed while event requests are being processed.
CSS Style Rules
.v-textfield { }The HTML structure of TextField is extremely simple, consisting only of an element with the v-textfield style.
For example, the following custom style uses dashed border:
.v-textfield-dashing {
border: thin dashed;
background: white; /* Has shading image by default */
}See the on-line example.
The result is shown in Styling TextField with CSS.
The style name for TextField is also used in several components that contain a text input field, even if the text input is not an actual TextField. This ensures that the style of different text input boxes is similar.