TAMZ. JavaME. MIDlets. Department of Computer Science VŠB-Technical University of Ostrava

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1 MIDlets 1

2 MIDlet A MIDlet is a Java program for embedded devices, more specifically the virtual machine. Generally, these are games and applications that run on a cell phone. MIDlets will (should) run on any device that implements MIDP. Like all Java programs, MIDlets are compile once, run anywhere. A MIDlet must extend the MIDlet class found in the javax.microedition.midlet package. 2

3 Life cycle A MIDlet goes through several phases as part of its life cycle and is always considered to be in on of three states. MIDlet() Paused startapp() pauseapp() Active destroyapp() destroyapp() Destroyed AMS reclaims MIDlet 3

4 Life cycle The MIDlet class serves as the gateway for communicating application-state changes to the AMS and vice versa. Startup MIDlet() Paused AMS pauseapp() startapp() destroyapp() Shutdown Running 4

5 Structure MIDlet should not have a main() method. If one is found then Application Management Software (AMS) ignores it. public class Empty extends MIDlet { protected void startapp() throws MIDletStateChangeException { } protected void pauseapp() { } } protected void destroyapp(boolean unconditional) throws MIDletStateChangeException { } 5

6 Creation Compilation Pre-verification Packaging.java.class.class manifest.txt.jar Internet.jad Deploying 6

7 MIDlet Suite This collection of MIDlets encapsulated in a JAR file is referred to as a MIDlet suite. MIDlets within a MIDlet suite share a common name space for persistent storage, runtime object heap, and static fields in classes. The contents of the MIDlet suite s JAR file include the following components: the class files implementing the MIDlets, any resource files used by the MIDlets: for example, icon or image files, and so forth, a manifest describing the JAR contents. 7

8 MIDlet Suite's Manifest File The JAR manifest specification provides for name-value pairs which MIDP uses to encode MIDlet attributes. These attributes can be retrieved by a MIDlet using the getappproperty() method. All attribute names that start with "MIDlet-" are reserved for use by the MIDP expert group to define MIDlet attributes. The following attributes must be in the JAR manifest: MIDlet-Name, MIDlet-Version, MIDlet-Vendor, A MIDlet-<n> for each MIDlet, MicroEdition-Profile, MicroEdition-Configuration. 8

9 MANIFEST.MF Example MIDlet-Name: TeaTime MIDlet Suite MIDlet-Version: MIDlet-Vendor: Krtek Polni MIDlet-1: TeaTime, /glasswatch.png, tea.timermidlet MIDlet-2: TeaEdit, /tea.png, tea.editor MicroEdition-Profile: MIDP-2.0 MicroEdition-Configuration: CLDC-1.1 9

10 In addition to the JAR file, the MIDP provides for a separate and optional file called the application descriptor. The application descriptor allows the system to verify that the associated MIDlet suite is suited to the device before loading the full JAR file of the MIDlet suite. It also allows MIDlet attributes to be supplied to the MIDlet suite without modifying the JAR file. The following attributes must be in the JAD manifest: MIDlet-Name, MIDlet-Version, MIDlet-Vendor, MIDlet-Jar-URL, MIDlet-Jar-Size. Application Descriptor 10

11 JAR File Contents The getresourceasstream() method of class Class gives access to resources stored in JAR file. META-INF/ META-INF/MANIFEST.MF tea/ tea/timermidlet.class tea/tea.class tea/counddownform.class glasswatch.png warning.png Class c = getclass(); InputStream input = c.getresourceasstream("/meta-inf/manifest.mf"); 11

12 Persistent Record Store 12

13 Persistent Storage Persistent storage is a non-volatile place for storing the state of objects. The MIDP provides a mechanism for MIDlets to persistently store data and retrieve it later. This mechanism is a simple record-oriented database called the Record Management System (RMS). A record store consists of a collection of records which will remain persistent across multiple invocations of the MIDlet. 13

14 Record Store Records are uniquely identified within a given record store by their id, which is an integer value. This id is used as the primary key for the records. The first record created in a record store will have id equal to one. RecordStore store = RecordStore.openRecordStore("contacts", true); String user = byte[] data = user.getbytes(); int id = store.addrecord(data, 0, data.length);... store.setrecord(id, data, 0, data.length);... store.deleterecord(id); store.closerecordstore(); Open/create record store Add record Update record Delete record Close RS 14

15 Accessing records as Data Stream The record store can be accessed as data stream to extract required data parts of the records via ByteArrayInputStream: DataInputStream in = new DataInputStream( new ByteArrayInputStream(storedData.getRecord(i))); in.readint(); in.readboolean(); in.readint(); in.readutf(); ByteArrayOutputStream bytes = new ByteArrayOutputStream(); DataOutputStream out = new DataOutputStream(bytes); out.writeboolean(selectedvalue[i]); out.flush(); byte [] b = bytes.tobytearray(); if (storeddata.getnumrecords() > 0) //detection usable if we store 1 record else storeddata.setrecord(1, b, 0, b.length); storeddata.addrecord(b, 0, b.length); 15

16 Enumerating Records The RecordEnumeration logically maintains a sequence of the ids of the records in a record store. An optional RecordFilter can be used to choose a subset of the records that match the supplied filter. By using an optional RecordComparator, the enumerator can index through the records in an order determined by the comparator. RecordStore store = RecordStore.openRecordStore("contacts", false); RecordEnumeration records = store.enumeraterecords(null, null, false); while (records.hasnextelement()) { //also haspreviouselement() byte[] record = records.nextrecord(); //also previousrecord() //nextrecordid(), previousrecordid() } RecordFilter the implementing class decides subset of records to be used in matches(byte[]) method. RecordComparator the implementation decides order of returned records in compare(byte[], byte[]) method keepupdated should enumeration reflect RS changes? Slower if true. 16

17 GUI 17

18 UI Classes Display Alert Choice List StringItem 0..1 Screen TextBox ImageItem Displayable Form TextField Canvas 0..* DateField Item Gauge ChoiceGroup 18

19 Display Each MIDlet has a reference to one Display object. This object can retrieve information about the current display and includes methods for requesting visual objects to be displayed. The Display object is best thought of as the manager of the display controlling what is shown on the device and when. private Display display; public Welcome() { super(); display = Display.getDisplay(this);... 19

20 Displayable A Displayable is an object that has the capability of being placed on the display. There are two types of Displayable object. Canvas Low-level objects that allow the application to provide the graphics and handle input. Screen High-level object that encapsulates a complete user interface component (for example, classes Alert, List, TextBox, or Form). 20

21 Low-Level User Interface The low-level user interface API for Canvas is designed for applications that need precise placement and control of graphic elements, as well as need access to lowlevel input events. Typical examples are a game board, a chart object, or a graph. Using the low-level user interface API, an application can: control what is drawn on the display, handle primitive events like key presses and releases, access concrete keys and other input devices. 21

22 High-Level User Interface The high-level user interface API is designed for business applications whose client components run on mobile information devices. To achieve portability, the high-level user interface API employes a high level of abstraction and provides very little control over look and feel. Drawing to the display is performed by the device's system software. Applications do not define the visual appearance (such as shape, color, font, and so forth) of the components. Navigation, scrolling, and other primitive interactions with the user interface components are performed by the device. The application is not aware of these interactions. Applications cannot access concrete input mechanisms, such as individual keys. 22

23 List The List class is a Screen that contains a list of choices. Each choice has an associated string and may have an icon. List objects may be created as one of the three types: exclusive, multiple and implicit. 23

24 List Initialization Implicit Lists can be used to construct menus by providing operations as List elements. List list = new List("Select...", List.IMPLICIT); for (int i = 0; i < teas.size(); i++) { Tea tea = (Tea)teas.elementAt(i); list.append(tea.getname(), null); } list.setcommandlistener(this); display.setcurrent(list); 24

25 Selection in Implicit List When the user performs select operation in implicit list, the system will invoke the select command by notifying the List's CommandListener. The default select command is the system-provided command SELECT_COMMAND. public void commandaction(command c, Displayable d) { if (c == List.SELECT_COMMAND) { List list = (List)d; int index = list.getselectedindex();... } else if (c == select) {... 25

26 TextBox The TextBox class defines a Screen that allows the user to enter and edit text. String title = tea + " Description"; String description =... TextBox text = new TextBox(title, description, 256, TextField.ANY); text.addcommand(save); text.addcommand(cancel); display.setcurrent(text); 26

27 Alert Alerts are best used in informational or error messages that stay on the screen for a short period of time and then disappear. Alert alert = new Alert("Tea Time"); alert.settimeout(alert.forever); alert.settype(alerttype.alarm); alert.setstring("your tea has... "); alert.setimage(image); display.setcurrent(alert); 27

28 Form A Form is a Screen that may contain a combination of Items including Strings, Images, editable TextFields, editable DateFields, Gauges and ChoiceGroups. Any of the subclasses of Item. An item may be placed within at most one Form. If the application attempts to place an item into a Form, and the item is already owned by this or another Form, an Illegal- StateException is thrown. 28

29 Form Item Management Items contained within a Form may be edited using append(), delete(), insert(), and set() methods. TextField name = new TextField("Name", "", 16, TextField.ANY); TextField time = new TextField("Infuse...", "", 4, TextField.NUMERIC); TextField description = Form form = new Form("Tea..."); form.append(name); form.append(time); form.addcommand(save); form.addcommand(cancel); form.setcommandlistener(this); 29

30 Exclusive and Multiple Choice A ChoiceGroup is a group of selectable elements intended to be placed within a Form. ChoiceGroup group =... // Choice.EXCLUSIVE int index = group.getselectedindex(); // Choice.MULTIPLE boolean[] selected; group.getselectedflags(selected); 30

31 Popup Choice The selection behavior of a popup choice is identical to that of an exclusive choice. However, a popup choice differs from an exclusive choice in presentation and interaction. In a popup choice, the selected element should always be displayed, and the other elements should remain hidden until the user performs a specific action to show them. ChoiceGroup group = new ChoiceGroup("Select...", Choice.POPUP); 31

32 Gauge Implements a graphical display, such as a bar graph, of an integer value. The Gauge contains a current value that lies between zero and the maximum value, inclusive. A Gauge may be interactive or non-interactive. Gauge gauge = new Gauge(null, true, tea.gettime(), 0); append(gauge); while (gauge.getvalue() - gauge.getmaxvalue()) {... gauge.setvalue(gauge.getvalue() + 1); 32

A Ticker implements a ticker-tape, a piece of text that runs continuously across the display. The direction and the speed of scrolling are determined by the device. Tickers can be set on any Screen.

33 A Ticker implements a ticker-tape, a piece of text that runs continuously across the display. The direction and the speed of scrolling are determined by the device. Tickers can be set on any Screen. A Ticker object can be shared between Screens, so that when switching between Screens the message appears continuously. Ticker Screen screen =... screen.setticker(new Ticker("Select a tea to infuse")); 33

34 Commands Since the MIDP user interface is highly abstract, it does not dictate any concrete user interaction technique such as soft buttons or menus. MIDP applications define Commands, and the implementation can provide user control over these with buttons, menus, or whatever mechanisms are appropriate for the device. 34

35 Command Listener Pattern The CommandListener interface is used by applications which need to receive high-level events from the implementation. An application will provide an implementation of a CommandListener and will then provide the instance to the addcommand method on a Displayable in order to receive high-level events on that screen. Command 0-* Displayable 0-1 CommandListener addcommand() removecommand() setcommandlistener() commandaction() 35

36 Command Registration Command yes = new Command("Yes", Command.OK, 0); Command no = new Command("No", Command.BACK, 0); Displayable warning = new WarningMessage(... warning.addcommand(yes); warning.addcommand(no); warning.setcommandlistener(this); Display display = Display.getDisplay(this); display.setcurrent(warning); 36

37 Listener The application-level handling of commands is based on a listener model. Each Displayable object has a single listener. public class TeaTime extends MIDlet implements CommandListener { private Command yes, no; } public void commandaction(command c, Displayable d) { if (c == yes) { // Delete the tea from list.... } else if (c == no) { // Do nothing. } } 37

Menu Abstract commands that cannot be mapped onto physical buttons are placed in a menu and the label "Menu" is mapped onto one of the programmable buttons.

38 Menu Abstract commands that cannot be mapped onto physical buttons are placed in a menu and the label "Menu" is mapped onto one of the programmable buttons. cancel = new Command("Cancel", Command.BACK, 0); edit = new Command("Edit", Command.ITEM, 1); create = new Command("Create New", Command.ITEM, 1); delete = new Command("Delete", Command.ITEM, 1); 38

39 ItemState Listener The ItemStateListener interface is used by applications which need to receive high-level events that indicate changes in the internal state of the interactive items within a Form screen. An application will provide an implementation of a ItemStateListener method itemstatechanged() and register the listener for a given form by calling the method setitemstatelistener(listener); The method processes following events, connected with user interaction: Selection changes in the ChoiceGroups Adjustments of the Gauges Editation of the TextFields Date and Time changes in the DateFields 39

Mobile Information Device Profile (MIDP) Alessandro Cogliati. Helsinki University of Technology Telecommunications Software and Multimedia Laboratory

Multimedia T-111.5350 Mobile Information Device Profile (MIDP) Alessandro Cogliati Helsinki University of Technology Telecommunications Software and Multimedia Laboratory 1 Outline Java Overview (Editions/Configurations/Profiles)