android通过led实现手电筒功能

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.FLASHLIGHT" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.flash" />

import android.hardware.Camera;
import android.hardware.Camera.Parameters;
import android.os.AsyncTask;

/**
 *Caution: On some devices, this method may take a long time to complete. It is best 
 *to call this method from a worker thread (possibly using android.os.AsyncTask) to 
 *avoid blocking the main application UI thread.
 */

public class FlashlightUtil extends AsyncTask<String, String, String> {

 private Camera camera;
 private int cameraId = 0; // 此功能目前不实用，这里不做实现 ， 但不能删除
 private Parameters parameters;
 public boolean isTorch = false;
 private boolean canFinish = false;
 private static FlashlightUtil flashlightUtil;

 private FlashlightUtil() {

 }

 /**
  * 设置手电筒开关，打开或关闭手电筒，根据手电筒的状态来设置相反的状态 void 2016年1月12日
  */
 public static void setSwitch() {
  if (null == flashlightUtil) {
   flashlightUtil = new FlashlightUtil();
   flashlightUtil.execute("");
  }
  flashlightUtil.setONOFF();
 }

 @Override
 protected String doInBackground(String... params) {
  // TODO Auto-generated method stub

  while (!canFinish) {
   if (null == camera) {
    camera = Camera.open(cameraId);
   }
   parameters = camera.getParameters();
   if (isTorch) {
    if (parameters.getFlashMode().equals(Parameters.FLASH_MODE_OFF)) {
     // 打开镁光灯
     parameters.setFlashMode(Parameters.FLASH_MODE_TORCH);
     camera.setParameters(parameters);
     camera.startPreview();
    }
   } else {
    if (parameters.getFlashMode().equals(
      Parameters.FLASH_MODE_TORCH)) {
     // 关闭镁光灯
     camera.stopPreview(); // 关掉亮灯
     camera.release(); // 关掉照相机
     camera = null;
    }
   }
  }

  return null;
 }

 /**
  * 此功能暂时关闭
  * @hide
  */
 public FlashlightUtil setCameraId(int cameraId) {
  this.cameraId = cameraId;
  return flashlightUtil;
 }

 /**
  * 打开关闭手电筒，默认第一次为打开 2016年1月12日
  */
 private void setONOFF() {
  isTorch = !isTorch;
 }


}

/**
 * 打开手电筒
 */
public void openFlashlight(View view) {
 FlashlightUtil.setSwitch() ;
}