我目前正在开发一个应用，该应用可以在用户手机上找到所有MP3，然后将其放入列表中。即使有很多歌曲，它也可以很好地运行并且非常快。现在，我为列表的每个项目填充了一个带有对象的新列表，然后将其显示在我的recyclerview中。问题是，我的手机上有700多首歌曲，这在相当长的一段时间内阻塞了UI线程。
现在，我想使用recyclerview而不是一次将列表中的所有项目全部加载到对象中，而是仅在它们将要显示时才加载-但我不知道如何执行此操作。现在，所有对象都已构建，然后在UI线程被阻塞30秒钟之后，从recyclerview中以非常长的滚动视图显示。可以请任何人帮我吗？这是我的代码：
namespace Media_Player
{
[Activity(Label = "Media_Player", MainLauncher = true)]
public class MainActivity : Activity
{
static public MediaPlayer mediaPlayer;
List<MP3object> mp3;
MediaMetadataRetriever reader;
public static Button btn_StartOrPause, btn_Stop;
public static TextView txt_CurrentSong;
public static bool stopIsActive = false, firstStart = true;
public static Android.Net.Uri CurrentActiveSongUri;
RecyclerView mRecyclerView;
RecyclerView.LayoutManager mLayoutManager;
PhotoAlbumAdapter mAdapter;
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
SetContentView(Resource.Layout.test);
reader = new MediaMetadataRetriever();
PopulateMP3List(ReturnPlayableMp3(true));
mediaPlayer = new MediaPlayer();
InitRecView();
}
private void InitRecView()
{
// Instantiate the adapter and pass in its data source:
mAdapter = new PhotoAlbumAdapter(mp3);
// Get our RecyclerView layout:
mRecyclerView = FindViewById<RecyclerView>(Resource.Id.recyclerView);
// Plug the adapter into the RecyclerView:
mRecyclerView.SetAdapter(mAdapter);
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.SetLayoutManager(mLayoutManager);
}
private void PopulateMP3List(List<string> content)
{
mp3 = new List<MP3object>();
foreach (string obj in content)
{
WriteMetaDataToFileList(obj);
}
}
void WriteMetaDataToFileList(string obj)
{
reader.SetDataSource(obj);
//Write Mp3 as object to global list
MP3object ob = new MP3object();
{
if(reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyTitle) != "" && reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyTitle) != null)
{
ob.SongName = reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyTitle);
}
else
{
ob.SongName = Resources.GetString(Resource.String.Unknown);
}
if (reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyArtist) != "" && reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyArtist) != null)
{
ob.ArtistName = reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyArtist);
}
else
{
ob.ArtistName = Resources.GetString(Resource.String.Unknown);
}
if (reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyAlbum) != "" && reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyAlbum) != null)
{
ob.AlbumName = reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyAlbum);
}
else
{
ob.AlbumName = Resources.GetString(Resource.String.Unknown);
}
if (reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyYear) != "" && reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyYear) != null)
{
ob.Year = reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyYear);
}
else
{
ob.Year = Resources.GetString(Resource.String.Unknown);
}
if (reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyYear) != "" && reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyYear) != null)
{
ob.Year = reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyYear);
}
else
{
ob.Year = Resources.GetString(Resource.String.Unknown);
}
ob.Mp3Uri = obj; // can never be unknown!
ob.DurationInSec = int.Parse(reader.ExtractMetadata(MediaMetadataRetriever.MetadataKeyDuration)) / 1000; // can never be unknown, div by 1000 to get sec not millis
}
mp3.Add(ob);
}
public List<string> ReturnPlayableMp3(bool sdCard)
{
List<string> res = new List<string>();
string phyle;
string path1 = null;
if(sdCard) // get mp3 from SD card
{
string baseFolderPath = "";
try
{
bool getSDPath = true;
Context context = Application.Context;
Java.IO.File[] dirs = context.GetExternalFilesDirs(null);
foreach (Java.IO.File folder in dirs)
{
bool IsRemovable = Android.OS.Environment.InvokeIsExternalStorageRemovable(folder);
bool IsEmulated = Android.OS.Environment.InvokeIsExternalStorageEmulated(folder);
if (getSDPath ? IsRemovable && !IsEmulated : !IsRemovable && IsEmulated)
baseFolderPath = folder.Path;
}
}
catch (Exception ex)
{
Console.WriteLine("GetBaseFolderPath caused the following exception: {0}", ex);
}
string xy = baseFolderPath.Remove(18); // This is result after this, but this hard coded solution could be a problem on different phones.: "/storage/05B6-2226/Android/data/Media_Player.Media_Player/files"
path1 = xy;
// path to SD card and MUSIC "/storage/05B6-2226/"
}
else // get Mp3 from internal storage
{
path1 = Android.OS.Environment.ExternalStorageDirectory.ToString();
}
var mp3Files = Directory.EnumerateFiles(path1, "*.mp3", SearchOption.AllDirectories);
foreach (string currentFile in mp3Files)
{
phyle = currentFile;
res.Add(phyle);
}
return res;
}
}
public class PhotoViewHolder : RecyclerView.ViewHolder
{
public ImageView Image { get; private set; }
public TextView Caption { get; private set; }
public PhotoViewHolder(View itemView) : base(itemView)
{
// Locate and cache view references:
Image = itemView.FindViewById<ImageView>(Resource.Id.imageView);
Caption = itemView.FindViewById<TextView>(Resource.Id.textView);
}
}
public class PhotoAlbumAdapter : RecyclerView.Adapter
{
public List<MP3object> mp3;
public PhotoAlbumAdapter(List<MP3object> mp3)
{
this.mp3 = mp3;
}
public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
{
View itemView = LayoutInflater.From(parent.Context).
Inflate(Resource.Layout.lay, parent, false);
PhotoViewHolder vh = new PhotoViewHolder(itemView);
return vh;
}
public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
{
PhotoViewHolder vh = holder as PhotoViewHolder;
vh.Caption.Text = mp3[position].SongName;
}
public override int ItemCount
{
get { return mp3.Count(); }
}
}
}
因此，获取带有Mp3位置的字符串列表的工作非常迅速，但是随后出现了“ WriteMetaDataToFileList（obj）”（来自“ PopulateMP3List（列表内容）”），这花费了很长时间。我认为我需要的是recyclerview只构建前20个对象，并且当用户开始滚动时，构建下20个对象并将它们附加到列表中，以便它们也可以滚动。请在这里帮助我:)
答案 0 :(得分：1)
这是一个抽象类：
public abstract class PaginationScrollListener extends RecyclerView.OnScrollListener {
private LinearLayoutManager linearLayoutManager;
protected PaginationScrollListener(LinearLayoutManager linearLayoutManager) {
this.linearLayoutManager = linearLayoutManager;
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
int visibleItemCount = linearLayoutManager.getChildCount();
int totalItemCount = linearLayoutManager.getItemCount();
int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
if (!isLoading() && !isLastPage()) {
if ((visibleItemCount + firstVisibleItemPosition) >= totalItemCount && firstVisibleItemPosition >= 0) {
loadMoreItems();
}
}
}
protected abstract void loadMoreItems();
public abstract boolean isLastPage();
public abstract boolean isLoading();
}
并且在适配器中，您必须遵循以下模式：
public class ConsultancyAdapter extends RecyclerView.Adapter<ConsultancyAdapter.ConsultancyVH> {
private static final int ITEM = 0;
private static final int LOADING = 1;
private boolean isLoadingAdded = false;
public ConsultancyAdapter(List<Consultancy> consultancies, ConsultancyAdapterListener listener) {
}
@NonNull
@Override
public ConsultancyVH onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
RecyclerView.ViewHolder viewHolder = null;
LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
switch (viewType) {
case ITEM:
viewHolder = getViewHolder(parent, layoutInflater);
break;
case LOADING:
View v2 = layoutInflater.inflate(R.layout.item_progress, parent, false);
viewHolder = new ConsultancyVH(v2);
break;
}
return (ConsultancyVH) viewHolder;
}
@NonNull
private RecyclerView.ViewHolder getViewHolder(ViewGroup parent, LayoutInflater inflater) {
RecyclerView.ViewHolder viewHolder;
View v1 = inflater.inflate(R.layout.item_consultancy, parent, false);
viewHolder = new ConsultancyVH(v1);
return viewHolder;
}
@Override
public void onBindViewHolder(@NonNull ConsultancyVH holder, int position) {
Consultancy consultancy = consultancies.get(position);
switch (getItemViewType(position)) {
case ITEM:
ConsultancyVH mySingeCounseller = holder;
holder.title.setText(consultancy.getTitle()); // set cardTitle
holder.fieldArea.setText(consultancy.getField_filedoctorskills());
break;
case LOADING:
break;
}
}
@Override
public int getItemCount() {
return consultancies.size();
}
@Override
public int getItemViewType(int position) {
return (position == consultancies.size() - 1 && isLoadingAdded) ? LOADING : ITEM;
}
public void add(Consultancy mc) {
consultancies.add(mc);
notifyItemInserted(consultancies.size() - 1);
}
public void addAll(List<Consultancy> mcList) {
for (Consultancy mc : mcList) {
add(mc);
}
}
public void remove(Consultancy city) {
int position = consultancies.indexOf(city);
if (position > -1) {
consultancies.remove(position);
notifyItemRemoved(position);
}
}
public Consultancy getItem(int position) {
return consultancies.get(position);
}
public void clear() {
isLoadingAdded = false;
while (getItemCount() > 0) {
remove(getItem(0));
}
}
public boolean isEmpty() {
return getItemCount() == 0;
}
public void addLoadingFooter() {
isLoadingAdded = true;
add(new Consultancy());
}
public void removeLoadingFooter() {
isLoadingAdded = false;
int position = consultancies.size() - 1;
Consultancy item = getItem(position);
if (item != null) {
consultancies.remove(position);
notifyItemRemoved(position);
}
}
public interface ConsultancyAdapterListener {
void onCaseClicked(int position, String nid, String fieldArea, String title);
}
protected class ConsultancyVH extends RecyclerView.ViewHolder {
private TextView title, fieldArea;
private CircleImageView iconProfile;
private MaterialRippleLayout caseButtonRipple;
public ConsultancyVH(View itemView) {
super(itemView);
caseButtonRipple = itemView.findViewById(R.id.case_button_ripple);
this.title = itemView.findViewById(R.id.docName);
this.fieldArea = itemView.findViewById(R.id.fieldArea);
this.iconProfile = itemView.findViewById(R.id.icon_profile);
}
}
}
以及您的活动：
private void setScrollListener() {
recyclerView.addOnScrollListener(new PaginationScrollListener(linearLayoutManager) {
@Override
protected void loadMoreItems() {
isLoading = true;
currentPage += 1;
loadNextPage();
}
@Override
public boolean isLastPage() {
return isLastPage;
}
@Override
public boolean isLoading() {
return isLoading;
}
});
loadFirstPage();
}
在我的loadFirstPage中，我与一个API对话，您需要一些代码：
private void loadFirstPage() {
CallData().enqueue(new DefaultRetrofitCallback<List<Consultancy>>() {
@Override
protected void onFailure(Throwable t) {
super.onFailure(t);
}
@Override
protected void onSuccess(List<Consultancy> response) {
swipeRefreshLayout.setRefreshing(false);
dataList = response;
adapter.addAll(dataList);
recyclerView.setAdapter(adapter);
if (!checkLast(response)) adapter.addLoadingFooter();
else isLastPage = true;
}
@Override
protected void onOtherStatus(Response<List<Consultancy>> response) {
super.onOtherStatus(response);
}
@Override
protected void always() {
super.always();
}
});
}
和loadNextPage：
private void loadNextPage() {
CallData().enqueue(new DefaultRetrofitCallback<List<Consultancy>>() {
@Override
protected void onFailure(Throwable t) {
super.onFailure(t);
}
@Override
protected void onSuccess(List<Consultancy> response) {
swipeRefreshLayout.setRefreshing(false);
adapter.removeLoadingFooter();
isLoading = false;
swipeRefreshLayout.setRefreshing(false);
adapter.addAll(response);
if (!checkLast(response)) adapter.addLoadingFooter();
else isLastPage = true;
}
@Override
protected void onOtherStatus(Response<List<Consultancy>> response) {
super.onOtherStatus(response);
}
@Override
protected void always() {
super.always();
}
});
}