在/ sdcard中创建目录失败

Question

我一直在尝试以/sdcard编程方式创建一个目录,但它无法正常工作.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

这里有三件事需要考虑:

1. 不要假设SD卡安装在/sdcard(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获取SD卡的位置:

   Environment.getExternalStorageDirectory();
   

2. 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"/>
   

3. 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> = 6.0(API级别23),则不仅需要包括

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

在你的AndroidManifest.xml中,还要在调用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) 

除此以外:

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,阅读官方文档.

另一种选择,也许你需要使用mkdirs而不是mkdir

file.mkdirs()

创建由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Android 6发生了这种情况并且编译目标> = 23,请不要忘记我们现在正在使用运行时权限.因此,在清单中提供权限已经不够了.

Answer 6

使用mkdirs()而不是mkdir()..它对我有用:)

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");