如何在安卓中访问下载文件夹？

我是新的机器人，我正在制作一个应用程序，您可以在其中将文件下载到下载文件夹（使用下载管理器）。如果我去模拟器中的下载文件夹，我可以看到图片。因此，如果我想显示下载文件的幻灯片，如何访问该文件夹？其次，如何在此代码中添加进度条：--

import java.util.Arrays;

import android.app.Activity;
import android.app.DownloadManager;
import android.app.DownloadManager.Query;
import android.app.DownloadManager.Request;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;

public class Download_managerActivity extends Activity {
     private long quueue_for_url;

     private DownloadManager dm;

        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);

            BroadcastReceiver receiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
                    String action = intent.getAction();

                    if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(action)) {
                        long downloadId = intent.getLongExtra(
                                DownloadManager.EXTRA_DOWNLOAD_ID, 0);
                        Query query = new Query();
                        query.setFilterById(quueue_for_url);
                        Cursor c = dm.query(query);
                        if (c.moveToFirst()) {
                            int columnIndex = c
                                    .getColumnIndex(DownloadManager.COLUMN_STATUS);
                            if (DownloadManager.STATUS_SUCCESSFUL == c
                                    .getInt(columnIndex)) {

                                ImageView view = (ImageView) findViewById(R.id.imageView1);
                                String uri_String_abcd = c
                                        .getString(c
                                                .getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));
                                view.setImageURI(Uri.parse(uri_String_abcd));

                            }
                        }
                    }
                }
            };

            registerReceiver(receiver, new IntentFilter(
                    DownloadManager.ACTION_DOWNLOAD_COMPLETE));
        }

        public void onClick(View view) {
            dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);

            Request request_for_url = new Request(
                    Uri.parse("http://fc03.deviantart.net/fs14/i/2007/086/9/1/Steve_Jobs_portrait_by_tumb.jpg"));

            Request request_for_url1 = new Request(
                    Uri.parse("http://2.bp.blogspot.com/_q7Rxg4wqDyc/S5ZRVLxVYuI/AAAAAAAAAvU/fQAUZ2XFcp8/s400/katrina-kaif.jpg"));
            Request request_for_url2 = new Request(
                    Uri.parse("http://www.buzzreactor.com/sites/default/files/Bill-Gates1.jpg"));

            quueue_for_url = dm.enqueue(request_for_url);
            quueue_for_url = dm.enqueue(request_for_url1);
            quueue_for_url = dm.enqueue(request_for_url2);

        }

        public void showDownload(View view) {
            Intent i = new Intent();
            //try more options to show downloading , retrieving and complete
            i.setAction(DownloadManager.ACTION_VIEW_DOWNLOADS);
            startActivity(i);
        }
    }

我想添加一个按钮，该按钮执行从下载文件夹中拍摄图片的功能，然后像幻灯片一样显示。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="cmpe235.lab1"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="9" />

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

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".Download_managerActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
</manifest>

主要.xml：-

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">


    <Button android:text="Start Download" android:id="@+id/button1"
        android:layout_width="wrap_content" android:layout_height="wrap_content"
         android:layout_gravity="center_vertical|center_horizontal|center" android:textColor="#0000A0" 
         android:typeface="serif" android:onClick="onClick"></Button>

    <Button android:text="View Downloads" android:id="@+id/button2"
        android:layout_width="wrap_content" android:layout_height="wrap_content"
         android:layout_gravity="center_vertical|center_horizontal|center" android:textColor="#0000A0" 
         android:typeface="serif" android:onClick="showDownload"></Button>

    <ImageView android:layout_height="wrap_content" android:id="@+id/imageView1"
        android:src="@drawable/icon" android:layout_width="wrap_content"></ImageView>

</LinearLayout>