Android - - ช่วยดูโค้ดให้ทีค่ะ อยากให้มันโชว์ไฟล์ของ ftp server แต่พอรันโค้ดแล้วมมัน error T^T

private List <String> getSD()
{
 List <String> it = new ArrayList <String>();
 File f = new File ("/mnt/sdcard/picture");
 File[] files = f.listFiles ();
 
 for (int i = 0; i <files.length; i++)
 {
 	File  file = files[i];
 	Log.d("Count",file.getPath());
  it.add (file.getPath());
 }
 return it;
}

public class MainActivity extends Activity {

   
	@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
       
        
        task getson = new task();
        getson.execute();
        
       List<String> Listfile = null ;
       Listfile = checkFiles(client);
       System.out.println("showfile uuu :: "+ Listfile);  
      

       
      //String[] FileList = null;  //new String[] {"1","2","3","4","5","6"};
       
     // listView1
        final ListView lisView1 = (ListView)findViewById(R.id.listView1);
       
       // System.out.println("show :: "+ Listfile);
     
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
				android.R.layout.simple_list_item_1,  Listfile);
        lisView1.setAdapter(adapter);
    }

    FTPClient client;

    public FTPClient connectWithFTP() throws IOException{
         client = new FTPClient();  
         try {

             client.connect("server", 21);  
             client.login("username", "password");
             System.out.println("status :: " + client.getReplyString());
             int reply = client.getReplyCode();
                if (!FTPReply.isPositiveCompletion(reply)) {
                    throw new Exception("Connect failed: " + client.getReplyString());
                }
                try {
                    client.enterLocalPassiveMode();
                    if (!client.setFileType(FTP.BINARY_FILE_TYPE)) {
                        Log.v(getClass().toString(), "Setting binary file type failed.");
                    }
                } catch(Exception e) {
                    e.printStackTrace();
                } 
             List<String> aa = checkFiles(client);
             System.out.println("check :: " +aa);
        } catch (Exception e) {
            System.out.println("status :: " + client.getReplyString());
        }
          return client;
    }

    private class task extends AsyncTask <Void, Void, FTPClient> {

        @Override
        protected void onPreExecute() {
            // Do stuff before the operation
        }


        @Override
        protected FTPClient doInBackground(Void... params) {
            FTPClient ftp = null;
            try {
                ftp = connectWithFTP();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }
    }

    public void disconnectWithFTP() throws IOException{
        client.logout();  
        client.disconnect();  
    }

   
   
    private List<String> checkFiles(FTPClient clients){
    	List<String> it = new ArrayList<String>();
          try {  
              FTPFile[] ftpFiles = clients.listFiles();  
              int length = ftpFiles.length;  
       
              for (int i = 0; i < length; i++) {  
                String name = ftpFiles[i].getName();                  
                it.add (name);
                
                Log.v("aasd", name);
             
              }    // System.out.println("showfile :: "+ it);
            } catch(Exception e) {  
              e.printStackTrace();  
            }  
          //System.out.println("showfile lol :: "+ it);
          return it;
    }

 
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/tableLayout1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
 
   	<TableRow
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" >
     
     <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="ListView and Checkbox : "
        android:layout_span="1"
        android:textAppearance="?android:attr/textAppearanceMedium" />
  	        
 	</TableRow>


	<View
		android:layout_height="1dip"
		android:background="#CCCCCC" />
	
  <RelativeLayout
      	android:layout_gravity="center_vertical|center_horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">

 	 <Button
 	     android:id="@+id/btnCheckAll"
 	     android:layout_width="wrap_content"
 	     android:layout_height="wrap_content"
 	     android:layout_alignParentLeft="true"
 	     android:layout_alignParentTop="true"
 	     android:layout_marginLeft="49dp"
 	     android:text="Check All" />

 	 <Button
 	     android:id="@+id/btnClearAll"
 	     android:layout_width="wrap_content"
 	     android:layout_height="wrap_content"
 	     android:layout_alignParentTop="true"
 	     android:layout_marginLeft="36dp"
 	     android:layout_toRightOf="@+id/btnCheckAll"
 	     android:text="Clear All" />
 	 
 	</RelativeLayout>
 	
  <LinearLayout
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.1">   
     
     <ListView
         android:id="@+id/listView1"
         android:layout_width="match_parent"
         android:layout_height="wrap_content">
     </ListView>
  	        
 	</LinearLayout>
 	
  <RelativeLayout
      	android:layout_gravity="center_vertical|center_horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">

 	 <Button
 	     android:id="@+id/btnGetItem"
 	     android:layout_width="wrap_content"
 	     android:layout_height="wrap_content"
 	     android:layout_alignParentTop="true"
 	     android:layout_centerHorizontal="true"
 	     android:text="Get Item Checked" />
 	 
 	</RelativeLayout>
 	
	<View
		android:layout_height="1dip"
		android:background="#CCCCCC" />
   		  
   	
	
</TableLayout>