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

String	MEDIA_BAD_REMOVAL	在没有挂载前存储媒体已经被移除。
String	MEDIA_CHECKING	正在检查存储媒体。
String	MEDIA_MOUNTED	存储媒体已经挂载，并且挂载点可读/写。
String	MEDIA_MOUNTED_READ_ONLY	存储媒体已经挂载，挂载点只读。
String	MEDIA_NOFS	存储媒体是空白或是不支持的文件系统。
String	MEDIA_REMOVED	存储媒体被移除。
String	MEDIA_SHARED	存储媒体正在通过USB共享。
String	MEDIA_UNMOUNTABLE	存储媒体无法挂载。
String	MEDIA_UNMOUNTED	存储媒体没有挂载。

Fields

public static String	DIRECTORY_ALARMS	系统提醒铃声存放的标准目录。
public static String	DIRECTORY_DCIM	相机拍摄照片和视频的标准目录。
public static String	DIRECTORY_DOWNLOADS	下载的标准目录。
public static String	DIRECTORY_MOVIES	电影存放的标准目录。
public static String	DIRECTORY_MUSIC	音乐存放的标准目录。
public static String	DIRECTORY_NOTIFICATIONS	系统通知铃声存放的标准目录。
public static String	DIRECTORY_PICTURES	图片存放的标准目录。
public static String	DIRECTORY_PODCASTS	系统广播存放的标准目录。
public static String	DIRECTORY_RINGTONES	系统铃声存放的标准目录。

Public Methods

static File	getDataDirectory() 获得android data的目录。
static File	getDownloadCacheDirectory() 获得下载缓存目录。
static File	getExternalStorageDirectory() 或者外部存储媒体目录。
static File	getExternalStoragePublicDirectory(String type) Get a top-level public external storage directory for placing files of a particular type.
static String	getExternalStorageState() 获得当前外部储存媒体的状态。
static File	getRootDirectory() 获得android的跟目录。

public static File getExternalStoragePublicDirectory (String type)

Since: API Level 8

Get a top-level public external storage directory for placing files of a particular type. This is where the user will typically place and manage their own files, so you should be careful about what you put here to ensure you don’t erase their files or get in the way of their own organization.

Here is an example of typical code to manipulate a picture on the public external storage:

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();
}

Parameters

type

The type of storage directory to return. Should be one of DIRECTORY_MUSIC,DIRECTORY_PODCASTS,DIRECTORY_RINGTONES,DIRECTORY_ALARMS,DIRECTORY_NOTIFICATIONS,DIRECTORY_PICTURES,DIRECTORY_MOVIES,DIRECTORY_DOWNLOADS, orDIRECTORY_DCIM. May not be null.

Returns

• Returns the File path for the directory. Note that this directory may not yet exist, so you must make sure it exists before using it such as withFile.mkdirs().