switch between internal and external sdcard

frontend/apps/filemanager/filemanager.lua

@@ -641,7 +641,7 @@ function FileManager:tapPlus()
         table.insert(buttons, 3, {
             {
                 text = _("Import files here"),
-                enabled = Device.isValidPath(self.file_chooser.path),
+                enabled = Device:isValidPath(self.file_chooser.path),
                 callback = function()
                     local current_dir = self.file_chooser.path
                     UIManager:close(self.file_dialog)
@@ -651,6 +651,32 @@ function FileManager:tapPlus()
         })
     end
 
+    if Device:hasExternalSD() then
+        table.insert(buttons, 4, {
+            {
+                text_func = function()
+                    if Device:isValidPath(self.file_chooser.path) then
+                        return _("Switch to SDCard")
+                    else
+                        return _("Switch to internal storage")
+                    end
+                end,
+                callback = function()
+                    if Device:isValidPath(self.file_chooser.path) then
+                        local ok, sd_path = Device:hasExternalSD()
+                        UIManager:close(self.file_dialog)
+                        if ok then
+                            self.file_chooser:changeToPath(sd_path)
+                        end
+                    else
+                        UIManager:close(self.file_dialog)
+                        self.file_chooser:changeToPath(Device.home_dir)
+                    end
+                end,
+            },
+        })
+    end
+
     self.file_dialog = ButtonDialogTitle:new{
         title = BD.dirpath(filemanagerutil.abbreviate(self.file_chooser.path)),
         title_align = "center",

frontend/device/android/device.lua

@@ -93,6 +93,7 @@ local Device = Generic:new{
         return android.openLink(link) == 0
     end,
     canImportFiles = function() return android.app.activity.sdkVersion >= 19 end,
+    hasExternalSD = function() return android.getExternalSdPath() end,
     importFile = function(path) android.importFile(path) end,
     canShareText = yes,
     doShareText = function(text) android.sendText(text) end,

frontend/device/generic/device.lua

@@ -45,6 +45,7 @@ local Device = {
     needsTouchScreenProbe = no,
     hasClipboard = yes, -- generic internal clipboard on all devices
     hasEinkScreen = yes,
+    hasExternalSD = no, -- or other storage volume that cannot be accessed using the File Manager
     canHWDither = no,
     canHWInvert = no,
     canUseCBB = yes, -- The C BB maintains a 1:1 feature parity with the Lua BB, except that is has NO support for BB4, and limited support for BBRGB24