Android -- Environment类

1、讲述 Environment 类
Environment 是一个提供访问环境变量的类。

Environment 包含常量：

MEDIA_BAD_REMOVAL
解释：返回getExternalStorageState() ，表明SDCard 被卸载前己被移除

MEDIA_CHECKING
解释：返回getExternalStorageState() ，表明对象正在磁盘检查。

MEDIA_MOUNTED
解释：返回getExternalStorageState() ，表明对象是否存在并具有读/写权限

MEDIA_MOUNTED_READ_ONLY
解释：返回getExternalStorageState() ，表明对象权限为只读

MEDIA_NOFS
解释：返回getExternalStorageState() ，表明对象为空白或正在使用不受支持的文件系统。

MEDIA_REMOVED
解释：返回getExternalStorageState() ，如果不存在 SDCard 返回

MEDIA_SHARED
解释：返回getExternalStorageState() ，如果 SDCard 未安装 ，并通过 USB 大容量存储共享 返回

MEDIA_UNMOUNTABLE
解释：返回getExternalStorageState() ，返回 SDCard 不可被安装 如果 SDCard 是存在但不可以被安装

MEDIA_UNMOUNTED
解释：返回getExternalStorageState() ，返回 SDCard 已卸掉如果 SDCard 是存在但是没有被安装

Environment 常用方法：
方法：getDataDirectory()
解释：返回 File ，获取 Android 数据目录。

方法：getDownloadCacheDirectory()
解释：返回 File ，获取 Android 下载/缓存内容目录。

方法：getExternalStorageDirectory()
解释：返回 File ，获取外部存储目录即 SDCard

方法：getExternalStoragePublicDirectory(String type)
解释：返回 File ，取一个高端的公用的外部存储器目录来摆放某些类型的文件

方法：getExternalStorageState()
解释：返回 File ，获取外部存储设备的当前状态

方法：getRootDirectory()
解释：返回 File ，获取 Android 的根目录

2、讲述 StatFs 类
StatFs 一个模拟linux的df命令的一个类,获得SD卡和手机内存的使用情况

StatFs 常用方法:

getAvailableBlocks()
解释：返回 Int ，获取当前可用的存储空间

getBlockCount()
解释：返回 Int ，获取该区域可用的文件系统数

getBlockSize()
解释：返回 Int ，大小，以字节为单位，一个文件系统

getFreeBlocks()
解释：返回 Int ，该块区域剩余的空间

restat(String path)
解释：执行一个由该对象所引用的文件系统

Constants

Fields

Public Methods

public static File getExternalStoragePublicDirectory (String type)

void createExternalStoragePublicPicture() {// Create a path where we will place our picture in the user's// public pictures directory.  Note that you should be careful about// what you place here, since the user often manages these files.  For// pictures and other media owned by the application, consider// Context.getExternalMediaDir().File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);File file = new File(path, "DemoPicture.jpg");try {// Make sure the Pictures directory exists.path.mkdirs();// Very simple code to copy a picture from the application's// resource into the external file.  Note that this code does// no error checking, and assumes the picture is small (does not// try to copy it in chunks).  Note that if external storage is// not currently mounted this will silently fail.InputStream is = getResources().openRawResource(R.drawable.balloons);OutputStream os = new FileOutputStream(file);byte[] data = new byte[is.available()];is.read(data);os.write(data);is.close();os.close();// Tell the media scanner about the new file so that it is // 这一步非常重要！！// immediately available to the user.MediaScannerConnection.scanFile(this,new String[] { file.toString() }, null,new MediaScannerConnection.OnScanCompletedListener() {public void onScanCompleted(String path, Uri uri) {Log.i("ExternalStorage", "Scanned " + path + ":");Log.i("ExternalStorage", "-> uri=" + uri);}});} catch (IOException e) {// Unable to create file, likely because external storage is// not currently mounted.Log.w("ExternalStorage", "Error writing " + file, e);}
}void deleteExternalStoragePublicPicture() {// Create a path where we will place our picture in the user's// public pictures directory and delete the file.  If external// storage is not currently mounted this will fail.File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);File file = new File(path, "DemoPicture.jpg");file.delete();
}boolean hasExternalStoragePublicPicture() {// Create a path where we will place our picture in the user's// public pictures directory and check if the file exists.  If// external storage is not currently mounted this will think the// picture doesn't exist.File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);File file = new File(path, "DemoPicture.jpg");return file.exists();
}