我无法创建文件到外部存储

Question

我不知道为什么createtempfile()失败，我已经设置了读写权限。

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="john.god.com.whereitssnap">

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



xxx.class

//storageDir = /storage/emulated/0/Pictures
File storageDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);


File image = File.createTempFile(imageFileName,".jpg", storageDir);
//logcat show nothing, it's empty
Log.i("image ",""+image );