我正在创建一个活动，通过＆＃39; .mp4＆＃39;来显示设备中的文件（包括外部存储空间）。 ListView中的扩展名。
这是活动文件
public class FindVideoActivity extends AppCompatActivity {
private List<String> fileNames;
private ListView lv;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_find_video);
fileNames = new ArrayList<>();
lv = (ListView) findViewById(R.id.find_video_list);
updateFileList();
}
public void updateFileList() {
String path;
String extension = Environment.getExternalStorageState();
if(extension.equals(Environment.MEDIA_MOUNTED)) {
path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/videostreaming/";
} else {
path = Environment.MEDIA_UNMOUNTED;
}
File file = new File(path);
ArrayAdapter<String> fileList = new ArrayAdapter<>(this, R.layout.file_list_item, fileNames);
VideoFinder finder = new VideoFinder();
File[] files = file.listFiles(finder);
for(File f: files) {
fileNames.add(f.getName());
}
lv.setAdapter(fileList);
}
}
为了过滤掉＆＃39; .mp4＆＃39;我创建了另一个类并将其命名为VideoFinder.java。该类实现java.io.FilenameFilter。这是代码。
public class VideoFinder implements FilenameFilter {
// overriding the method from the FilenameFilter interface.
@Override
public boolean accept(File dir, String filename) {
if(filename.endsWith(".mp4")) {
return true;
}
return false;
}
}
When I run the code above, it returns `NullPointerException` like the following.
Caused by: java.lang.NullPointerException
at com.marshall.videostreaming.FindVideoActivity.updateFileList(FindVideoActivity.java:46)
at com.marshall.videostreaming.FindVideoActivity.onCreate(FindVideoActivity.java:26)
所以它说for方法中的updateFileList()循环正在捕获异常。我仍然无法捕捉到此代码中缺少的内容。有人可以帮忙吗？
答案 0 :(得分：0)
检查您的路径，因为分配Environment.MEDIA_UNMOUNTED似乎不正确。还要检查Files是否为null，因为这就是你获得NPE的原因。
答案 1 :(得分：0)
我的主Java 类
/**
* Created by ravindra on 2/12/15.
*/
public class GalleryScreen extends Activity implements View.OnClickListener{
private ArrayList<String> file_path = new ArrayList<String>();
GridView gridview;
ImageView left_iv;
TextView header_tv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.gallery_screen);
Bundle bundle = getIntent().getExtras();
gettingIds();
gettingOnClickListener();
fetchDeviceGallery();
}
private void fetchDeviceGallery() {
String[] projection = {MediaStore.Images.Thumbnails._ID};
// Create the cursor pointing to the SDCard
Cursor cursor = managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI,
projection, // Which columns to return
null, // Return all rows
null,
MediaStore.Images.Thumbnails.IMAGE_ID);
// Get the column index of the Thumbnails Image ID
int columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID);
file_path = getFilePaths();
GalleryAdapter adapter = new GalleryAdapter(GalleryScreen.this,file_path);
gridview.setAdapter(adapter);
System.out.println("Gallery images================="+cursor.getCount()+" "+columnIndex);
}
private void gettingIds() {
gridview = (GridView) findViewById(R.id.gridview);
left_iv = (ImageView) findViewById(R.id.left_iv);
header_tv = (TextView) findViewById(R.id.header_tv);
gridview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
finish();
// overridePendingTransition(R.anim.left_to_right, R.anim.right_to_left);
}
});
}
private void gettingOnClickListener() {
left_iv.setOnClickListener(this);
}
public ArrayList<String> getFilePaths() {
Uri u = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
String[] projection = {MediaStore.Images.ImageColumns.DATA};
Cursor c = null;
SortedSet<String> dirList = new TreeSet<String>();
ArrayList<String> resultIAV = new ArrayList<String>();
String[] directories = null;
if (u != null) {
c = GalleryScreen.this.managedQuery(u, projection, null, null, null);
}
if ((c != null) && (c.moveToFirst())) {
do {
String tempDir = c.getString(0);
tempDir = tempDir.substring(0, tempDir.lastIndexOf("/"));
try {
dirList.add(tempDir);
} catch (Exception e) {
}
}
while (c.moveToNext());
directories = new String[dirList.size()];
dirList.toArray(directories);
}
for (int i = 0; i < dirList.size(); i++) {
File imageDir = new File(directories[i]);
File[] imageList = imageDir.listFiles();
if (imageList == null)
continue;
for (File imagePath : imageList) {
try {
if (imagePath.isDirectory()) {
imageList = imagePath.listFiles();
}
if (imagePath.getName().contains(".jpg") || imagePath.getName().contains(".JPG")
|| imagePath.getName().contains(".jpeg") || imagePath.getName().contains(".JPEG")
|| imagePath.getName().contains(".png") || imagePath.getName().contains(".PNG")
|| imagePath.getName().contains(".mp4") || imagePath.getName().contains(".MP4")
||imagePath.getName().contains(".mp3") || imagePath.getName().contains(".MP3"))
{
System.out.println("RESOURCES ARE====="+imagePath);
String path = imagePath.getAbsolutePath();
resultIAV.add(path);
}
// }
catch (Exception e) {
e.printStackTrace();
}
}
}
return resultIAV;
}
@Override
public void onClick(View v) {
switch (v.getId())
{
case R.id.left_iv:
finish();
overridePendingTransition(R.anim.left_to_right, R.anim.right_to_left);
break;
}
}
@Override
public void onBackPressed() {
super.onBackPressed();
finish();
overridePendingTransition(R.anim.left_to_right, R.anim.right_to_left);
}
}
它的适配器类如下： -
/**
* Created by ravindra on 2/12/15.
*/
public class GalleryAdapter extends BaseAdapter {
private final DisplayImageOptions options;
private final ImageLoader imageLoader;
Activity activity;
ArrayList<String> arrayList = new ArrayList<String>();
public GalleryAdapter(Activity activity, ArrayList<String> arrayList) {
this.activity = activity;
this.arrayList = arrayList;
imageLoader = ImageLoader.getInstance();
ImageLoader.getInstance().init(ImageLoaderConfiguration.createDefault(activity));
options = new DisplayImageOptions.Builder()
.showImageOnLoading(R.drawable.loader)
.showImageForEmptyUri(R.drawable.loader)
.showImageOnFail(R.drawable.loader)
.cacheInMemory(true)
.cacheOnDisk(true)
.considerExifParams(true)
.bitmapConfig(Bitmap.Config.RGB_565)
.build();
}
@Override
public int getCount() {
return arrayList.size();
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
public class ViewHolder {
ImageView gallery_item;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
final ViewHolder _viewHolder;
if (convertView == null) {
_viewHolder = new ViewHolder();
LayoutInflater _layInflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = _layInflater.inflate(R.layout.gallery_item, null);
_viewHolder.gallery_item = (ImageView) convertView.findViewById(R.id.gallery_item);
convertView.setTag(_viewHolder);
} else {
_viewHolder = (ViewHolder) convertView.getTag();
}
if (arrayList.get(position).contains(".mp3") || arrayList.get(position).contains(".MP3"))
{
_viewHolder.gallery_item.setImageResource(R.drawable.audio_img);
}
else {
imageLoader.displayImage("file://" + arrayList.get(position), _viewHolder.gallery_item, options, null);
}
return convertView;
}
}