MidletSuite、Midlet、Schedule、Display、MidletState代码解析

只看该作者 · 2010-3-2 11:44

com.sun.midp.main.Main.java文件是midp的起点；里面有main、manage、runLocalClass等函数；在runLocalClass中，创建了MIDletSuite，并创建MIDlet：

MIDletSuite midletSuite;
try {
// assume a class name of a MIDlet in the classpath
midletSuite = DevMIDletSuiteImpl.create(internalSecurityToken,
state.descriptorName,
state.midletClassName,
DEV_STORAGE_NAME,
state.securityDomain);
// if no class name was specified than repeat the selector
do {
if (!Scheduler.getScheduler().schedule(midletSuite)) {
// shutdown
break;
}
} while (state.midletClassName == null);
} catch (Throwable e) {
e.printStackTrace();
}

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DevMIDletSuiteImpl是MIDletSuiteImpl的子类，而MIDletSuiteImpl实现了MIDletSuite接口；

Scheduler类实现了MIDletEventListener和SystemEventListener接口；其中MIDletEventListener接口定义了方法startMIDlet、pauseMIDlet、destroyMIDlet；SystemEventListener接口定义了方法shutdown；此外，Scheduler还实现了方法schedule和getScheduler方法；getScheduler静态方法创建了Scheduler实例；schedule方法从MIDletSuite中取出MIDlet的名称，并调用MIDletState类的静态方法createMIDlet创建一个MIDlet的对象；

MIDletState类用于管理MIDlet的状态；这是一个抽象类，主要的抽象方法有：

protected abstract void startApp() throws MIDletStateChangeException;
protected abstract void pauseApp();
protected abstract void destroyApp(boolean unconditional)
throws MIDletStateChangeException;

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createMIDlet方法根据传入的MIDlet名称，创建了一个MIDlet：

static MIDlet createMIDlet(String classname) throws
ClassNotFoundException, InstantiationException,
IllegalAccessException {
Class midletClass;
Object midlet;
synchronized (createMIDletLock) {
try {
allowedToCreateMIDlet = true;
midletClass = Class.forName(classname);
midlet = midletClass.newInstance();
if (midlet instanceof MIDlet) {
return (MIDlet)midlet;
}
throw new InstantiationException("Class not a MIDlet");
} finally {
allowedToCreateMIDlet = false;
}
}
}

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在MIDlet的构造中，创建了MIDletProxy对象；MIDletProxy类是MIDletState抽象类的子类；在它的静态构造中，创建了MIDletStateMapImpl的对象；

在MIDletState的构造中，做了Display初始化相关的大量工作：

首先调用Display类的静态构造函数，通过DeviceCaps读取设备相关的信息，然后创建了DisplayManager的实例，还创建了一个不断循环等待唤醒的事件监听器，这是MIDP程序事件驱动的根源；

static {
/* done this way because native access to static fields is hard */
DeviceCaps c = new DeviceCaps();
WIDTH = c.width;
HEIGHT = c.height;
ADORNEDHEIGHT = c.adornedHeight;
ERASE_COLOR = c.eraseColor;
DISPLAY_DEPTH = c.displayDepth;
DISPLAY_IS_COLOR = c.displayIsColor;
POINTER_SUPPORTED = c.pointerSupported;
MOTION_SUPPORTED = c.motionSupported;
REPEAT_SUPPORTED = c.repeatSupported;
IS_DOUBLE_BUFFERED = c.isDoubleBuffered;
FG_COLOR = 0;
BG_H_COLOR = FG_COLOR;
FG_H_COLOR = ERASE_COLOR;
Text.FG_COLOR = FG_COLOR;
Text.FG_H_COLOR = FG_H_COLOR;
ALPHA_LEVELS = c.numAlphaLevels;
KEYCODE_UP = c.keyCodeUp;
KEYCODE_DOWN = c.keyCodeDown;
KEYCODE_LEFT = c.keyCodeLeft;
KEYCODE_RIGHT = c.keyCodeRight;
KEYCODE_SELECT = c.keyCodeSelect;
c = null; // let the DeviceCaps instance be garbage collected
/* Let com.sun.midp classes call in to this class. */
displayManagerImpl = new DisplayManagerImpl();
DisplayManagerFactory.SetDisplayManagerImpl(displayManagerImpl);
deviceAccess = new DisplayDeviceAccess();
eventHandler = getEventHandler();
screenGraphics = Graphics.getGraphics(null);
}

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MIDletState的的构造还通过创建的DisplayManager的实例创建Display的构造：并创建Display类中另一个私有类DisplayAccess的对象；DisplayManager是MIDP中所有显示的控制器，DisplayAccess被DisplayManager驱动，这两个类都来自于DisplayEvent接口，却分工不同；

protected MIDletState(MIDlet m) {
DisplayAccess accessor;
midlet = m;
state = PAUSED_RESUME; // So it will be made active soon
scheduler = Scheduler.getScheduler();
mutex = scheduler.getMutex();
synchronized (createMIDletLock) {
if (!allowedToCreateMIDlet) {
MIDletSuite suite = scheduler.getMIDletSuite();
if (suite != null) {
suite.checkIfPermissionAllowed(Permissions.AMS);
}
}
}
// Force the creation of the Display
displayManager = DisplayManagerFactory.getDisplayManager();
accessor = displayManager.createDisplay(classSecurityToken, midlet);
display = accessor.getDisplay();
if (scheduler.getMIDletSuite().isTrusted()) {
accessor.setTrustedIcon(classSecurityToken, true);
}
}

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最后，对这一部分遇到的类及其关系做一个总结：

MIDlet相关：

MIDletSuite接口；MIDletSuiteImpl类实现了MIDletSuite接口；

MIDletState类：实现了startApp、pauseApp等改变MIDlet状态的函数，这是一个抽象类；MIDletProxy是该抽象类的实现类；

MIDletStateMap接口：MIDletStateMapImpl：根据MIDlet可在map中查找该MIDlet对应的状态；

MIDlet类：抽象类；实现了getAppPropery、platformRequest等方法；

Schedule类：调度类，决定使用midletsuite中的哪个midlet并改变其状态；

Display相关：

Display类：MIDPUI相关的根本类；DisplayAccess和DisplayManagerImpl是Display的私有类；DisplayManagerImpl在Display的静态构造中创建，并在DisplayManagerImpl的createDisplay中创建Display和DisplayAccess的对象；

MidletSuite、Midlet、Schedule、Display、MidletState代码解析

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