android手机用闪光灯做成手电筒的应用非常多，可是有的不能用。

后来发现是除了把 camera device的 flashmode设置成torch外还要打开预览：

以下是代码：

MainActivity.java

package com.android.flashlight;

import android.app.Activity;

import android.os.Bundle;

import android.view.MotionEvent;

import android.widget.ImageView;

public class MainActivity extends Activity{

	private FlashlightSurface mSurface;

	private ImageView mImageView;

	private boolean isFlashlightOn = false;

	@Override

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);

		setContentView(R.layout.main);

		Contants.LogI("MainActivity: onCreate()");

		mSurface = (FlashlightSurface) findViewById(R.id.surfaceview);

		mImageView = (ImageView) findViewById(R.id.image);

	}

	@Override

	public boolean onTouchEvent(MotionEvent event) {

		if(MotionEvent.ACTION_UP == event.getAction()){

			Contants.LogI("MainActivity: onTouchEvent() : ACTION_UP");

			if(isFlashlightOn){

				mSurface.setFlashlightSwitch(false);

				isFlashlightOn = false;

				mImageView.setImageResource(R.drawable.flashlight_off);

			}else{

				mSurface.setFlashlightSwitch(true);

				isFlashlightOn = true;

				mImageView.setImageResource(R.drawable.flashlight_on);

			}

		}

		return super.onTouchEvent(event);

	}

}

FlashlightSurface.java

package com.android.flashlight;

import android.content.Context;

import android.graphics.PixelFormat;

import android.hardware.Camera;

import android.util.AttributeSet;

import android.view.SurfaceHolder;

import android.view.SurfaceView;

public class FlashlightSurface extends SurfaceView implements SurfaceHolder.Callback{

	private SurfaceHolder mHolder;

	private Camera mCameraDevices;

	private Camera.Parameters mParameters;

	public FlashlightSurface(Context context, AttributeSet attrs) {

		super(context, attrs);

		Contants.LogI("FlashlightSurface");

		mHolder = this.getHolder();

		mHolder.addCallback(this);

		mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

	}

	@Override

	public void surfaceChanged(SurfaceHolder holder, int format, int width,

			int height) {

		Contants.LogI("surfaceChanged");

		mParameters = mCameraDevices.getParameters();

		if(mParameters != null)

			mParameters.setPictureFormat(PixelFormat.JPEG);

		mParameters.setPreviewSize(320, 480);

		mParameters.setPictureSize(320, 480);

		mCameraDevices.setParameters(mParameters);

		mCameraDevices.startPreview();

	}

	@Override

	public void surfaceCreated(SurfaceHolder holder) {

		Contants.LogI("surfaceCreated");

		try {

			mCameraDevices = Camera.open();

			mCameraDevices.setPreviewDisplay(mHolder);

		} catch (Exception e) {

			if(mCameraDevices != null)

				mCameraDevices.release();

			mCameraDevices = null;

		}

	}

	@Override

	public void surfaceDestroyed(SurfaceHolder holder) {

		Contants.LogI("surfaceDestroyed");

		if(mCameraDevices == null) return;

		mCameraDevices.stopPreview();

		mCameraDevices.release();

		mCameraDevices = null;

	}

	/**

	 * 设置手电筒的开关状态

	 * @param on ： true则打开，false则关闭

	 */

	public void setFlashlightSwitch(boolean on){

		if(mCameraDevices == null) return;

		if(mParameters == null){

			mParameters = mCameraDevices.getParameters();

		}

		if(on){

			mParameters.setFlashMode(Contants.FLASH_MODE_TORCH);

		}else{

			mParameters.setFlashMode(Contants.FLASH_MODE_OFF);

		}

		Contants.LogI("setFlashlightSwitch-----------------" + on);

		mCameraDevices.setParameters(mParameters);

	}

}

布局文件main.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent" >

    <com.android.flashlight.FlashlightSurface

        android:id="@+id/surfaceview"

        android:layout_width="fill_parent"

    	android:layout_height="fill_parent"

        ></com.android.flashlight.FlashlightSurface>

    <ImageView

        android:id="@+id/image"

        android:layout_width="fill_parent"

    	android:layout_height="fill_parent"

    	android:src="@drawable/flashlight_off"

    	android:background="#FFFFFFFF"

        />

</RelativeLayout>

显然这里打开了一个预览，可是被图片盖上了，看不见而已。不然闪光灯不亮。

这里有个Demo：http://download.csdn.net/detail/liu_zhen_wei/4801779

包含widget窗体小部件的使用方法和手电筒的功能实现，安装后，加入窗体小部件（手电筒）到桌面，然后点击小部件后，打开手电筒的界面

点击界面，实现 打开/关闭 手电筒。