闪光灯的开启和关闭

package com.loaderman.flashlightdemo;

import android.hardware.Camera;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
    private       Button            statusButton = null;
    private       Camera            camera       = null;
    private       Camera.Parameters parameters   = null;
    public static boolean           statusFlag   = true;
    private       int               back         = 0;// 判断按几次back

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        statusButton = (Button) findViewById(R.id.statusButton);
        statusButton.setOnClickListener(new Mybutton());
    }
    class Mybutton implements View.OnClickListener {
        @Override
        public void onClick(View v) {
            if (statusFlag) {
                statusButton.setText("关闭闪光灯");
                camera = Camera.open();
                parameters = camera.getParameters();
                parameters.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);// 开启
                camera.setParameters(parameters);
                statusFlag = false;
            } else {
                statusButton.setText("开启闪光灯");
                parameters.setFlashMode(Camera.Parameters.FLASH_MODE_OFF);// 关闭
                camera.setParameters(parameters);
                statusFlag = true;
                camera.release();
            }
        }
    }

    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            back++;
            CloseApp();
        }
        return false;// 设置成false让back失效 ，true表示 不失效

    }

    public void CloseApp() { // 关闭程序
        if (statusFlag) {// 开关关闭时
            this.finish();
            android.os.Process.killProcess(android.os.Process.myPid());// 关闭进程
        } else if (!statusFlag) {// 开关打开时
            camera.release();
            this.finish();
            android.os.Process.killProcess(android.os.Process.myPid());// 关闭进程
            statusFlag = true;// 避免，打开开关后退出程序，再次进入不打开开关直接退出时，程序错误
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"

    tools:context="com.loaderman.flashlightdemo.MainActivity">
    <Button
        android:id="@+id/statusButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="闪光灯" />
</RelativeLayout>

 添加权限:

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

 效果需在真机测试即可