上节讲了开发Android Things应用时常用的一些操作命令，不明白的可以查看http://www.jianshu.com/p/08f6785ff5aa

本节内容讲如何控制LED灯并闪烁， 先来看下电路连接图和实际效果图

电路连接图

实际效果图

准备材料

开发板

面包板

电阻

两根公-母杜邦线

LED灯

按效果图接好各个组件

创建AS工程并配置项目

在模块下的build.gradle需引入Android Things

provided 'com.google.android.things:androidthings:0.5.1-devpreview'

应用必须引入Android Things库，在节点下配置以下代码

在AndroidManifest.xml中，往节点中配置一个过滤器，表示设备启动时需要启动的类

具体代码

android:label="@string/app_name">

获取开发板的名称

Android Things支持的开发板有多种类型，所以引脚对应的名称也不一样，所以第一步先获取开发板的名称

private static String getBoardVariant() {

if (!sBoardVariant.isEmpty()) {

return sBoardVariant;

}

sBoardVariant = Build.DEVICE;

Log.e(TAG, sBoardVariant);

if (sBoardVariant.equals(DEVICE_EDISON)) {

PeripheralManagerService pioService = new PeripheralManagerService();

List gpioList = pioService.getGpioList();

if (gpioList.size() != 0) {

String pin = gpioList.get(0);

if (pin.startsWith("IO")) {

sBoardVariant = DEVICE_EDISON_ARDUINO;

}

}

}

return sBoardVariant;

}

sBoardVariant是一个静态变量，代表开发板的名称，如果已经有值则返回，没有则用Build.DEVICE获取开发板名字，获取到开发板名称后，如果开发板是edison系列，需要检查引脚前缀，因为edison和edison_arduino开发板用Build.DEVICE获取的名称相同，而引脚名称却不同，所以使用PeripheralManagerService外围设备管理器调用getGpioList()获取设备所有的Gpio引脚名称，在不为空的情况下，检查引脚名称是否以IO开头，如果是，则开发板的是edison_arduino，否则是edison。如果开发板不是edison就不需要检查，Build.DEVICE获取到的名称是开发板的真实名称。

获取连接LED灯的引脚名称

上一个步骤已经获取到开发板的名称，接下来通过开发板的名称获取引脚的名称

public static String getGPIOForLED() {

//getBoardVariant()为开发板的名称

switch (getBoardVariant()) {

case DEVICE_EDISON_ARDUINO:

return "IO13";

case DEVICE_EDISON:

return "GP45";

case DEVICE_JOULE:

return "J6_25";

case DEVICE_RPI3:

return "BCM6";

case DEVICE_IMX6UL_PICO:

return "GPIO4_IO22";

case DEVICE_IMX6UL_VVDN:

return "GPIO3_IO06";

case DEVICE_IMX7D_PICO:

return "GPIO_34";

default:

throw new IllegalStateException("Unknown Build.DEVICE " + Build.DEVICE);

}

}

我所使用的开发板是树莓派，所以连接LED灯的引脚名称是BCM6，这些名称如何得知需要看开发板的电路原理图，每个引脚的名称、用途会有说明，学的越来越底层了，～.~

打开引脚

//声明外围设备管理器

PeripheralManagerService service = new PeripheralManagerService();

//引脚名称

String pinName = BoardDefaults.getGPIOForLED();

//打开引脚

mLedGpio = service.openGpio(pinName);

//设置为输出引脚并初始化为低电平

mLedGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

//因为初始化输出引脚为低电平，所以LED灯不会亮，这是这是为true

//后LED会亮起来

mLedGpio.setValue(true)；

如何让LED灯闪烁起来

使用异步类实现，这里使用Handler

private Runnable mBlinkRunnable = new Runnable() {

@Override

public void run() {

try {

// 切换电平状态

mLedState = !mLedState;

mLedGpio.setValue(mLedState);

Log.d(TAG, "State set to " + mLedState);

// 每隔1000ms调用该接口

mHandler.postDelayed(mBlinkRunnable, 1000);

} catch (IOException e) {

Log.e(TAG, "Error on PeripheralIO API", e);

}

}

};

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

//运行接口

mHandler.post(mBlinkRunnable);

}

private Handler mHandler = new Handler();

以上实例是部分代码下面贴出完整的代码

获取LED引脚名称代码

import android.os.Build;

import android.util.Log;

import com.google.android.things.pio.PeripheralManagerService;

import java.util.List;

@SuppressWarnings("WeakerAccess")

public class BoardDefaults {

private static final String TAG = BoardDefaults.class.getName();

private static final String DEVICE_EDISON_ARDUINO = "edison_arduino";

private static final String DEVICE_EDISON = "edison";

private static final String DEVICE_JOULE = "joule";

private static final String DEVICE_RPI3 = "rpi3";

private static final String DEVICE_IMX6UL_PICO = "imx6ul_pico";

private static final String DEVICE_IMX6UL_VVDN = "imx6ul_iopb";

private static final String DEVICE_IMX7D_PICO = "imx7d_pico";

private static String sBoardVariant = "";

/**

* Return the GPIO pin that the LED is connected on.

* For example, on Intel Edison Arduino breakout, pin "IO13" is connected to an onboard LED

* that turns on when the GPIO pin is HIGH, and off when low.

*/

public static String getGPIOForLED() {

switch (getBoardVariant()) {

case DEVICE_EDISON_ARDUINO:

return "IO13";

case DEVICE_EDISON:

return "GP45";

case DEVICE_JOULE:

return "J6_25";

case DEVICE_RPI3:

return "BCM6";

case DEVICE_IMX6UL_PICO:

return "GPIO4_IO22";

case DEVICE_IMX6UL_VVDN:

return "GPIO3_IO06";

case DEVICE_IMX7D_PICO:

return "GPIO_34";

default:

throw new IllegalStateException("Unknown Build.DEVICE " + Build.DEVICE);

}

}

private static String getBoardVariant() {

if (!sBoardVariant.isEmpty()) {

return sBoardVariant;

}

sBoardVariant = Build.DEVICE;

Log.e(TAG, sBoardVariant);

// For the edison check the pin prefix

// to always return Edison Breakout pin name when applicable.

if (sBoardVariant.equals(DEVICE_EDISON)) {

PeripheralManagerService pioService = new PeripheralManagerService();

List gpioList = pioService.getGpioList();

if (gpioList.size() != 0) {

String pin = gpioList.get(0);

if (pin.startsWith("IO")) {

sBoardVariant = DEVICE_EDISON_ARDUINO;

}

}

}

return sBoardVariant;

}

}

让LED灯闪烁完整代码

/**

* Sample usage of the Gpio API that blinks an LED at a fixed interval defined in

* {@link #INTERVAL_BETWEEN_BLINKS_MS}.

*

* Some boards, like Intel Edison, have onboard LEDs linked to specific GPIO pins.

* The preferred GPIO pin to use on each board is in the {@link BoardDefaults} class.

*

*/

public class BlinkActivity extends Activity {

private static final String TAG = BlinkActivity.class.getSimpleName();

private static final int INTERVAL_BETWEEN_BLINKS_MS = 2000;

private Handler mHandler = new Handler();

private Gpio mLedGpio;

private boolean mLedState = false;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

Log.i(TAG, "Starting BlinkActivity");

PeripheralManagerService service = new PeripheralManagerService();

try {

String pinName = BoardDefaults.getGPIOForLED();

mLedGpio = service.openGpio(pinName);

mLedGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

Log.i(TAG, "Start blinking LED GPIO pin");

// Post a Runnable that continuously switch the state of the GPIO, blinking the

// corresponding LED

mHandler.post(mBlinkRunnable);

} catch (IOException e) {

Log.e(TAG, "Error on PeripheralIO API", e);

}

}

@Override

protected void onDestroy() {

super.onDestroy();

// Remove pending blink Runnable from the handler.

mHandler.removeCallbacks(mBlinkRunnable);

// Close the Gpio pin.

Log.i(TAG, "Closing LED GPIO pin");

try {

mLedGpio.close();

} catch (IOException e) {

Log.e(TAG, "Error on PeripheralIO API", e);

} finally {

mLedGpio = null;

}

}

private Runnable mBlinkRunnable = new Runnable() {

@Override

public void run() {

// Exit Runnable if the GPIO is already closed

if (mLedGpio == null) {

return;

}

try {

// Toggle the GPIO state

mLedState = !mLedState;

mLedGpio.setValue(mLedState);

Log.d(TAG, "State set to " + mLedState);

// Reschedule the same runnable in {#INTERVAL_BETWEEN_BLINKS_MS} milliseconds

mHandler.postDelayed(mBlinkRunnable, INTERVAL_BETWEEN_BLINKS_MS);

} catch (IOException e) {

Log.e(TAG, "Error on PeripheralIO API", e);

}

}

};

}

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