在/ SD卡中创build一个目录失败

我一直在尝试以编程方式在/sdcard创build一个目录，但它不工作。 下面的代码总是输出directory not created.

 boolean success = (new File("/sdcard/map")).mkdir(); if (!success) { Log.i("directory not created", "directory not created"); } else { Log.i("directory created", "directory created"); } 

Answer 1

这里有三件事要考虑：

1. 不要以为SD卡是安装在/sdcard （在默认情况下可能是true，但最好不要硬编码）。 你可以通过查询系统来获得SD卡的位置：

    Environment.getExternalStorageDirectory(); 

2. 您必须通知Android，您的应用程序需要通过在AndroidManifest.xml文件中添加一个uses-permission条目来写入外部存储：

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 

3. 如果这个目录已经存在，那么mkdir将返回false。 所以检查目录的存在，然后尝试创build它，如果它不存在。 在你的组件中，使用类似于：

    File folder = new File(Environment.getExternalStorageDirectory() + "/map"); boolean success = true; if (!folder.exists()) { success = folder.mkdir(); } if (success) { // Do something on success } else { // Do something else on failure } 

Answer 2

我更新我的Android手机到6.0（API级别23）后，我有同样的问题。 以下解决scheme对我有用。 希望它可以帮助你。

请检查您的Android版本。 如果它是> = 6.0（API级别23），则不仅需要包含

 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 

在你的AndroidManifest.xml中，也要在调用mkdir（）之前请求权限 。 代码snopshot。

 public static final int MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE = 1; public int mkFolder(String folderName){ // make a folder under Environment.DIRECTORY_DCIM String state = Environment.getExternalStorageState(); if (!Environment.MEDIA_MOUNTED.equals(state)){ Log.d("myAppName", "Error: external storage is unavailable"); return 0; } if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) { Log.d("myAppName", "Error: external storage is read only."); return 0; } Log.d("myAppName", "External storage is not read only or unavailable"); if (ContextCompat.checkSelfPermission(this, // request permission when it is not granted. Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) { Log.d("myAppName", "permission:WRITE_EXTERNAL_STORAGE: NOT granted!"); // Should we show an explanation? if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)) { // Show an expanation to the user *asynchronously* -- don't block // this thread waiting for the user's response! After the user // sees the explanation, try again to request the permission. } else { // No explanation needed, we can request the permission. ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE); // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an // app-defined int constant. The callback method gets the // result of the request. } } File folder = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM),folderName); int result = 0; if (folder.exists()) { Log.d("myAppName","folder exist:"+folder.toString()); result = 2; // folder exist }else{ try { if (folder.mkdir()) { Log.d("myAppName", "folder created:" + folder.toString()); result = 1; // folder created } else { Log.d("myAppName", "creat folder fails:" + folder.toString()); result = 0; // creat folder fails } }catch (Exception ecp){ ecp.printStackTrace(); } } return result; } @Override public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) { switch (requestCode) { case MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE: { // If request is cancelled, the result arrays are empty. if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) { // permission was granted, yay! Do the // contacts-related task you need to do. } else { // permission denied, boo! Disable the // functionality that depends on this permission. } return; } // other 'case' lines to check for other // permissions this app might request } } 

更多信息请阅读“ 在运行时请求权限 ”

Answer 3

SD卡的正确path是

 /mnt/sdcard/ 

但是，正如之前所回答的那样，您不应该对其进行硬编码。 如果你在Android 2.1或之后，使用

 getExternalFilesDir(String type) 

除此以外：

 Environment.getExternalStorageDirectory() 

仔细阅读https://developer.android.com/guide/topics/data/data-storage.html#filesExternal

另外，你需要使用这个方法或类似的东西

 boolean mExternalStorageAvailable = false; boolean mExternalStorageWriteable = false; String state = Environment.getExternalStorageState(); if (Environment.MEDIA_MOUNTED.equals(state)) { // We can read and write the media mExternalStorageAvailable = mExternalStorageWriteable = true; } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) { // We can only read the media mExternalStorageAvailable = true; mExternalStorageWriteable = false; } else { // Something else is wrong. It may be one of many other states, but all we need // to know is we can neither read nor write mExternalStorageAvailable = mExternalStorageWriteable = false; } 

然后检查你是否可以访问SD卡。 如上所述，阅读官方文档。

另一种select，也许你需要使用mkdirs而不是mkdir

 file.mkdirs() 

创build由该文件尾部文件名命名的目录，包括创build该目录所需的完整目录path。

Answer 4

重新启动您的Android设备。 我重新启动设备后，事情开始为我工作。

Answer 5

如果在Android 6中发生这种情况并编译target> = 23，请不要忘记我们现在使用运行时权限 。 所以在清单中给予权限是不够的。

Answer 6

使用mkdirs（）而不是mkdir（）..它为我工作:)

 File folder = new File(Environment.getExternalStorageDirectory()+"/Saved CGPA"); if(!folder.exists()){ if(folder.mkdirs()) Toast.makeText(this, "New Folder Created", Toast.LENGTH_SHORT).show(); } File sdCardFile = new File(Environment.getExternalStorageDirectory()+"/Saved CGPA/cgpa.html"); 

Answer 7

在android api> = 23

  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 

代替

  <app:uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 

Answer 8

您是否有权在清单中写入SD卡？ 在http://developer.android.com/reference/android/Manifest.permission.html查找WRITE_EXTERNAL_STORAGE

Answer 9

它不是已经创build了吗？ 如果文件夹已经存在mkdir，则Mkdir返回false

Answer 10

 File f = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/FoderName"); if (!f.exists()) { f.mkdirs(); } 

Answer 11

我犯了包括两个错误：

 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 

和：

 <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/> 

按以上顺序。 所以当我拿出第二个许可时，（READ），问题就消失了。