Android led灯实现大致流程-优快云博客

本文介绍了在Android系统中如何使用标准API控制LED灯的开关及闪烁，并分析了底层实现原理，指出在特定条件下（如来电或屏幕亮起）无法正常工作的原因。

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led灯的控制在http://gqdy365.iteye.com/admin/blogs/2208344中写的方法是直接通过操作led设置来控制灯的开关。这样做的问题是未按Android标准结构实现，可能存在潜在的问题，后面分析的一下灯的源码，原来Android系统里面已经提供的相关的实现。

Android系统标准的led可以通过发送通知来控制led灯，做法如下：


	private void notificactionLed() {
		NotificationManager manager = (NotificationManager) this
				.getSystemService(Context.NOTIFICATION_SERVICE);
		Notification notification = new Notification();
		notification.icon = R.drawable.ic_launcher;
		notification.tickerText = "发送灯通知";

		/**
		 * To turn the LED off, pass 0 in the alpha channel for colorARGB or 0 for both ledOnMS and ledOffMS. 
		   To turn the LED on, pass 1 for ledOnMS and 0 for ledOffMS. 
		   To flash the LED, pass the number of milliseconds that it should be on and off to ledOnMS and ledOffMS.
		 */
		notification.defaults = Notification.DEFAULT_LIGHTS;
		notification.ledARGB = 0xffffffff;//控制led灯的颜色

		//灯闪烁时需要设置下面两个变量
		notification.ledOnMS = 300;
		notification.ledOffMS = 300;

		notification.flags = Notification.FLAG_SHOW_LIGHTS;

		Intent intent = new Intent(this, MainActivity.class);
		PendingIntent pendingIntent = PendingIntent.getActivity(this, 0,
				intent, PendingIntent.FLAG_ONE_SHOT);

		notification.setLatestEventInfo(this, "灯测试", "led灯测试", pendingIntent);
		manager.notify(1, notification);
	}

通过查看灯的实现源码，发现如下问题：
在来电或者系统屏幕亮的情况下是没办法控制灯的，具体源码（com.android.server.NotificationManagerService）中是这样的：


private void More ...updateLightsLocked()
2229    {
2230        // handle notification lights
2231        if (mLedNotification == null) {
2232            // get next notification, if any
2233            int n = mLights.size();
2234            if (n > 0) {
2235                mLedNotification = mLights.get(n-1);
2236            }
2237        }
2238
2239        // Don't flash while we are in a call or screen is on
2240        if (mLedNotification == null || mInCall || mScreenOn) {
2241            mNotificationLight.turnOff();
2242        } else {
2243            final Notification ledno = mLedNotification.sbn.getNotification();
2244            int ledARGB = ledno.ledARGB;
2245            int ledOnMS = ledno.ledOnMS;
2246            int ledOffMS = ledno.ledOffMS;
2247            if ((ledno.defaults & Notification.DEFAULT_LIGHTS) != 0) {
2248                ledARGB = mDefaultNotificationColor;
2249                ledOnMS = mDefaultNotificationLedOn;
2250                ledOffMS = mDefaultNotificationLedOff;
2251            }
2252            if (mNotificationPulseEnabled) {
2253                // pulse repeatedly
2254                mNotificationLight.setFlashing(ledARGB, LightsService.LIGHT_FLASH_TIMED,
2255                        ledOnMS, ledOffMS);
2256            }
2257        }
2258    }

在com.android.server.LightsService中对灯的操作做了封装，所有灯的操作调用了：


116        private void More ...setLightLocked(int color, int mode, int onMS, int offMS, int brightnessMode) {
117            if (color != mColor || mode != mMode || onMS != mOnMS || offMS != mOffMS) {
118                if (DEBUG) Slog.v(TAG, "setLight #" + mId + ": color=#"
119                        + Integer.toHexString(color));
120                mColor = color;
121                mMode = mode;
122                mOnMS = onMS;
123                mOffMS = offMS;
124                setLight_native(mNativePointer, mId, color, mode, onMS, offMS, brightnessMode);
125            }
126        }

其中setLight_native方法是一个本地方法，代码在 frameworks/base/services/jni/com_android_server_LightsService.cpp中。
在com_android_server_LightsService中最终还是通过操作设备文件来实现灯的开关，文件位置如下：

[img]http://dl2.iteye.com/upload/attachment/0108/4915/92728da8-3488-3c04-820b-509ebd472d8d.png[/img]

参考资料：
http://blog.youkuaiyun.com/u011630458/article/details/22280841
http://blog.youkuaiyun.com/u011630458/article/details/22312901