外部存储不可用

Question

我想创建新文件并写入/读取应用程序设置。 isExternalStorageAvailable() 返回 false 并且应该为 true。 Android 模拟器外部内存 = 200mb。

 boolean isExternalStorageAvailable() {
        String extStorageState = Environment.getExternalStorageState();
        if (Environment.MEDIA_MOUNTED.equals(extStorageState)) {
            return true;
        }
        return false;
    }

添加了清单文件的权限：

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

代码：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (!isExternalStorageAvailable() || isExternalStorageReadOnly()) {
        saveButton.setEnabled(false);
        System.out.println("Available: "+isExternalStorageAvailable()+", ReadOnly: "+isExternalStorageReadOnly());
    }
    else {
        myExternalFile = new File(getExternalFilesDir(filepath), filename);
    }
}

Answer 1

要获取所有外部存储路径，可以使用：

    File[] extSDCardPaths = null;
    try {
        extSDCardPaths = ContextCompat.getExternalFilesDirs(ctx, null);
    } catch (Exception e) {
        // handle
    }

    for (File f : extSDCardPaths) {
        if (Environment.isExternalStorageRemovable(f)) {
            // check if anything found
        }
    }

如果extSDCardPaths 返回某些内容，则可以使用 ext 存储。

以上仅适用于 > 4.4(KitKat)

以下 hack 可用作较低操作系统版本的后备：

String[] fallback = {"/storage/sdcard1/", "/mnt/ext_card/", "/mnt/extSdCard/", "/storage/extsdcard/",
            "/mnt/extsdcard/", "/storage/extSdCard/", "/mnt/external_sd", "/storage/MicroSD/",
            "/storage/external_SD/", "/storage/ext_sd/", "/storage/removable/sdcard1/", "/mnt/sdcard/external_sd/",
            "/storage/ext_sd/", "/mnt/emmc/", "/data/sdext/", "/sdcard/sd/"};

   for (String path : fallback) {
        if (new File(path).exists()) {
                // found an ext. dir
            break;
        }
   }

Answer 2

如果您的应用程序以棉花糖或更高版本为目标并运行，您必须获得对外部存储的读/写权限，您必须在清单中声明权限后明确向用户请求权限。

1. 确保你的清单中有这个：<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

2. 明确检查权限。如果未提供，请索取：

   public void checkPermissionReadStorage(Activity activity){
            if (ContextCompat.checkSelfPermission(activity,      
   Manifest.permission.READ_EXTERNAL_STORAGE) !=     
   PackageManager.PERMISSION_GRANTED) {
   
           // Should we show an explanation?
           if (ActivityCompat.shouldShowRequestPermissionRationale(activity,
                   Manifest.permission.READ_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(activity,
                       new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                       MY_PERMISSIONS_REQUEST_READ_STORAGE);
   
               // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
               // app-defined int constant. The callback method gets the
               // result of the request.
           }
       }
   }
   

3. 接收权限响应：

   @Override
   public void onRequestPermissionsResult(int requestCode,
                                          String permissions[], int[] grantResults) {
       switch (requestCode) {
           case PermissionManager.MY_PERMISSIONS_REQUEST_READ_STORAGE:
               //premission to read storage
               if (grantResults.length > 0
                       && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
   
                   // Permission granted. Call your storage related code here
   
               } else {
   
                   // permission denied.
                   // Handle permission failed here.
               }
               return;
   
   
           // other 'case' lines to check for other
           // permissions this app might request
       }
   }
   

代码取自here