Question

我一直在尝试以编程方式在/sdcard中创建目录，但它无效。以下代码始终输出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

这里要考虑三件事：

不要假设sd卡安装在/sdcard（在默认情况下可能是真的，但最好不要硬编码。）。您可以通过查询系统来获取SD卡的位置：
```
Environment.getExternalStorageDirectory();
```
您必须通过在 AndroidManifest.xml 文件中添加uses-permission条目来通知Android您的应用程序需要写入外部存储：
```
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
```

如果此目录已存在，则mkdir将返回false。因此，请检查目录是否存在，然后尝试创建目录（如果该目录不存在）。在您的组件中，使用以下内容：

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

将Android手机更新为6.0（API级别23）后，我遇到了同样的问题。以下解决方案适用于我。希望它也能帮到你。

请检查你的Android版本。如果它是> = 6.0（API级别23），则不仅需要包括

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

在您的AndroidManifest.xml中

，但在调用mkdir（）之前还请求权限。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＆＃34; Requesting Permissions at Run Time＆＃34;

Answer 3

SD卡的正确路径是

/mnt/sdcard/

但是，如前所述，你不应该硬编码。如果您使用的是Android 2.1或之后，请使用

getExternalFilesDir(String type)

否则：

Environment.getExternalStorageDirectory()

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

此外，您还需要使用此方法或类似的方法

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;
}

然后检查您是否可以访问SD卡。如上所述，请阅读官方文档。

另一种选择，也许你需要使用mkdirs代替mkdir

file.mkdirs()

创建以此文件的尾随文件名命名的目录，包括创建此目录所需的完整目录路径。

Answer 4

重启您的Android设备。重新启动设备后，事情开始对我有用。

Answer 5

如果您使用Android 6并编译目标＆gt; = 23，请不要忘记我们现在正在使用runtime permissions。因此，在清单中提供权限已经不够了。

Answer 6

使用mkdirs（）而不是mkdir（）..它对我有效：）

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＆gt; = 23

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

而不是

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

Answer 8

您是否拥有在清单中写入SD卡的权限？在http://developer.android.com/reference/android/Manifest.permission.html

查找WRITE_EXTERNAL_STORAGE

Answer 9

是不是已经创建了？如果文件夹已经存在，则Mkdir返回false mkdir

Answer 10

您需要担心许多事情 1.如果您使用的是Android Bellow Marshmallow，那么您必须在Manifest File中设置permesions。 2.如果您正在使用更高版本的Android现在意味着从Marshmallow到Oreo 您必须转到应用程序信息并手动设置存储的应用程序权限。如果你想在运行时设置它，你可以通过下面的代码

来做到这一点

public  boolean isStoragePermissionGranted() {
if (Build.VERSION.SDK_INT >= 23) {
    if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE)
            == PackageManager.PERMISSION_GRANTED) {
        Log.v(TAG,"Permission is granted");
        return true;
    } else {

        Log.v(TAG,"Permission is revoked");
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
        return false;
    }
}
else { //permission is automatically granted on sdk<23 upon installation
    Log.v(TAG,"Permission is granted");
    return true;
}

}

Answer 11

我错误地将两者都包括在内：

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

和

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

按上述顺序。所以当我拿出第二个许可（READ）时，问题就消失了。

Answer 12

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

Answer 13

如果错误发生在 Android 6.0 和 API >=23 ;仅在 AndroidManifest.xml 中授予权限还不够。

你必须给运行时权限，你可以在这里参考更多 Runtime Permission

                       (or)

Google 在 Android Q 上有一个新功能：外部存储的过滤视图。一个快速解决方法是在 AndroidManifest.xml 文件中添加此代码：< /p>

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

    <!-- This attribute is "false" by default on apps targeting Android Q. -->
    <application android:requestLegacyExternalStorage="true">
     ...
     ...
    </application>
</manifest>

您可以在此处阅读更多相关信息：https://developer.android.com/training/data-storage/compatibility

内部存储与二级存储

内部存储在API中被称为“外部存储”；不是“二级存储”

Environment.getExternalStorageDirectory();

如 Environment 文档中所述

在/ sdcard中创建目录失败

13 个答案: