1.我下载market上的所有手电筒APP都是通过Camera打开闪光灯的方式来实现的，但是大部分APP在打开Camera时没有进行异常处理工作，也没有任何的提示，如果当其他的程序在使用Camera时，并且返回或点Home后没有释放Camera，这时在启动相应的手电筒APP就会出现崩溃或者手电筒功能已经失效，这种用户体验用户是不能接受的！

2,网上很多Camera打开闪光灯实现手电筒的源码，而且原理都是一样的，当然这些代码并没有错误，但存在的问题是这些源码在有的手机版本上能够实现相应的功能，在另外的手机版本上就不起作用了，在CSDN资源中的大部分手电筒Demo也都会存在此问题，兼容性不好！

我自己实现的这个手电筒很简单，没有任何的UI界面，进入APP后就直接照明，实现的原理就2点：

1.跟其他手电筒APP一样，用Camera打开闪光灯开始照明

2.将当前屏幕的背光调节为最亮状态，退出时在恢复之前的背光值

代码和布局如下：

MainActivity.java

package huahua.flashlight;import java.io.IOException;import android.app.Activity;import android.content.ContentResolver;import android.content.pm.FeatureInfo;import android.content.pm.PackageManager;import android.hardware.Camera;import android.os.Bundle;import android.provider.Settings;import android.provider.Settings.SettingNotFoundException;import android.util.Log;import android.view.SurfaceHolder;import android.view.SurfaceView;import android.view.Window;import android.view.WindowManager;import android.widget.Toast;/** * 花花手电筒 * @author huahua */public class MainActivity extends Activity implements SurfaceHolder.Callback{ private static final String TAG = "huahua"; /** * 进入APP时的背光亮度值 */ int normal; /** * 进入APP时，是否为自动调节亮度状态 */ boolean AutoBrightnessOpen = false; private Camera camera;  private SurfaceView surfaceView; private SurfaceHolder surfaceHolder; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //去除title this.requestWindowFeature(Window.FEATURE_NO_TITLE);  //去掉Activity上面的状态栏 getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);  setContentView(R.layout.activity_main); surfaceView = (SurfaceView) this.findViewById(R.id.surfaceview); surfaceHolder = surfaceView.getHolder(); surfaceHolder.addCallback(this); surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);  if(isAutoBrightness(getContentResolver())) { AutoBrightnessOpen = true; } normal = Settings.System.getInt(getContentResolver(),  Settings.System.SCREEN_BRIGHTNESS, 255);  PackageManager pm= this.getPackageManager(); FeatureInfo[] features=pm.getSystemAvailableFeatures(); for(FeatureInfo f : features) { if(PackageManager.FEATURE_CAMERA_FLASH.equals(f.name)) //判断设备是否支持闪光灯 { Log.d("huahua","支持闪光灯"); } } } @Override protected void onPause() { // TODO Auto-generated method stub super.onPause(); Closeshoudian(); } @Override protected void onResume() { // TODO Auto-generated method stub super.onResume(); Openshoudian(); } /** * 判断是否开启了自动亮度调节 * * @param aContext * @return */ public boolean isAutoBrightness(ContentResolver aContentResolver) { boolean automicBrightness = false; try {  automicBrightness = Settings.System.getInt(aContentResolver,   Settings.System.SCREEN_BRIGHTNESS_MODE) == Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC; } catch (SettingNotFoundException e) {  e.printStackTrace(); } return automicBrightness; } /** * 停止自动亮度调节 * * @param activity */ public void stopAutoBrightness(Activity activity) { Settings.System.putInt(activity.getContentResolver(),  Settings.System.SCREEN_BRIGHTNESS_MODE,  Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL); } /** * 恢复自动亮度调节 * * @param activity */ public void setAutoBrightness(Activity activity) { Settings.System.putInt(activity.getContentResolver(),  Settings.System.SCREEN_BRIGHTNESS_MODE,  Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC); } /** * 打开手电筒 */ public void Openshoudian() { //异常处理一定要加，否则Camera打开失败的话程序会崩溃 try {  Log.d("huahua","camera打开"); camera = Camera.open(); } catch (Exception e) { Log.d("huahua","Camera打开有问题"); Toast.makeText(MainActivity.this, "Camera被占用，请先关闭", Toast.LENGTH_SHORT).show(); } if(camera != null) { //打开闪光灯 camera.startPreview(); Camera.Parameters parameter = camera.getParameters(); parameter.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH); camera.setParameters(parameter); Log.d("huahua","闪光灯打开"); //先关闭自动调节背光功能，才可以调节背光 if(AutoBrightnessOpen) { stopAutoBrightness(MainActivity.this); } //将背光设置为最亮  WindowManager.LayoutParams lp = getWindow().getAttributes();  lp.screenBrightness = Float.valueOf(255) * (1f / 255f);  getWindow().setAttributes(lp); } } /** * 关闭手电筒 */ public void Closeshoudian() { if (camera != null) {  //关闭闪光灯  Log.d("huahua", "closeCamera()"); camera.getParameters().setFlashMode(Camera.Parameters.FLASH_MODE_OFF); camera.setParameters(camera.getParameters());  camera.stopPreview();  camera.release();  camera = null;  //恢复进入程序前的背光值  WindowManager.LayoutParams lp = getWindow().getAttributes();  lp.screenBrightness = Float.valueOf(normal) * (1f / 255f);  getWindow().setAttributes(lp);  //如果进入APP时背光为自动调节，则退出时需要恢复为自动调节状态 if(AutoBrightnessOpen) { setAutoBrightness(MainActivity.this); } } } @Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) { // TODO Auto-generated method stub } @Override public void surfaceCreated(SurfaceHolder holder) { try { if(camera != null) { camera.setPreviewDisplay(holder); } } catch (IOException e) { e.printStackTrace(); }  } @Override public void surfaceDestroyed(SurfaceHolder holder) { // TODO Auto-generated method stub }}

activity_main.xmlactivity_main.xml