blocks|key|912875|text|如果这种情况发生在你的Android6和编译目标>=+23上，别忘了我们现在使用的是runtime+permissions。因此，仅在清单中提供权限是不够的。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|912876|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.android.com/training/permissions/requesting.html^0|16|J|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

If this is happening to you with Android 6 and compile target >= 23, don't forget that we are now using <a href="http://developer.android.com/training/permissions/requesting.html" rel="noreferrer">runtime permissions</a>. So giving permissions in the manifest is not enough anymore.

blocks|key|912808|text|使用mkdirs()而不是mkdir()..it对我有效:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|912809|File+folder+=+new+File(Environment.getExternalStorageDirectory()%2B"/Saved+CGPA");
if(!folder.exists()){
++++if(folder.mkdirs())
++++Toast.makeText(this,+"New+Folder+Created",+Toast.LENGTH_SHORT).show();
}

File+sdCardFile+=+new+File(Environment.getExternalStorageDirectory()%2B"/Saved+CGPA/cgpa.html");|code-block|syntax|javascript|912810|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

use mkdirs() instead of mkdir()..it worked for me :)

<pre><code>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");
</code></pre>

blocks|key|1127812|text|在android+api+>=+23中|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1127813|++++<uses-permission+android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>|code-block|syntax|javascript|1127814|而不是|1127815|++++<app:uses-permission+android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>|1127816|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

in android api >= 23

<pre><code> &lt;uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/&gt;
</code></pre>

instead of

<pre><code> &lt;app:uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/&gt;
</code></pre>

blocks|key|912732|text|您是否拥有在清单中写入SD卡的正确权限？在http://developer.android.com/reference/android/Manifest.permission.html上查找WRITE_EXTERNAL_STORAGE|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|912733|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.android.com/reference/android/Manifest.permission.html^0|L|1Z|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Do you have the right permissions to write to SD card in your manifest ?
Look for WRITE_EXTERNAL_STORAGE at <a href="http://developer.android.com/reference/android/Manifest.permission.html" rel="nofollow">http://developer.android.com/reference/android/Manifest.permission.html</a>

blocks|key|1127710|text|它不是已经创建了吗？如果文件夹已经存在，则Mkdir返回false+mkdir|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1127711|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.android.com/reference/java/io/File.html#mkdir%2528%2529^0|Y|5|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Isn't it already created ? Mkdir returns false if the folder already exists too
<a href="http://developer.android.com/reference/java/io/File.html#mkdir%28%29" rel="nofollow">mkdir</a>

blocks|key|912927|text|你需要担心的事情有很多。1.如果你使用的是Android+Bellow棉花糖，那么你必须在Manifest文件中设置渗透。2.如果你正在使用更高版本的Android，意味着现在从棉花糖到奥利奥，你要么必须转到应用程序信息，并在那里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实现|type|unstyled|depth|inlineStyleRanges|entityRanges|data|912928|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;
}|code-block|syntax|javascript|912929|}|912930|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

There are Many Things You Need to worry about 
1.If you are using Android Bellow Marshmallow then you have to set permesions in Manifest File.
2. If you are using later Version of Android means from Marshmallow to Oreo now 
Either you have to go to the App Info and Set there manually App permission for Storage.
if you want to Set it at Run Time you can do that by below code

<pre><code>public boolean isStoragePermissionGranted() {
if (Build.VERSION.SDK_INT &gt;= 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&lt;23 upon installation
 Log.v(TAG,"Permission is granted");
 return true;
}
</code></pre>

}

blocks|key|1127762|text|我犯了一个错误，将两者都包括在内：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1127763|<uses-permission+android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>|code-block|syntax|javascript|1127764|和：|1127765|<uses-permission+android:name="android.permission.READ_EXTERNAL_STORAGE"/>|1127766|按照上面的顺序。所以当我拿出第二个许可时，这个问题就消失了。|1127767|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I made the mistake of including both:

<pre><code>&lt;uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/&gt;
</code></pre>

and:

<pre><code>&lt;uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/&gt;
</code></pre>

in the above order. So when I took out the second permission, (READ), the problem went away.

blocks|key|912845|text|File+f+=+new+File(Environment.getExternalStorageDirectory().getAbsolutePath()
++++++++%2B+"/FoderName");
if+(!f.exists())+{
++++f.mkdirs();
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|912846|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

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

I have been trying to create a directory in <code>/sdcard</code> programmatically, but it's not working. The code below always outputs <code>directory not created.</code>

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

Creating a directory in /sdcard fails

Android

我一直在尝试以编程方式在/sdcard中创建一个目录，但它不起作用。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 

问在/sdcard中创建目录失败
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问在/sdcard中创建目录失败EN

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问在/sdcard中创建目录失败
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