如何在 android 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，其中一个可以下载文件到下载文件夹(使用下载管理器)。我可以看到图片，如果我去下载文件夹在模拟器。因此，如果我想显示一个幻灯片下载的文件如何我可以访问该文件夹？其次，如何在代码中添加进度条: ——

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，执行从下载文件夹的图片，然后像幻灯片显示的功能。

<?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>

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>