在RecyclerViewAdapter中实现计时器

Question

I have problem with implementing countdown timers in RecyclerView. Data input to RecyclerView comes from Dialog, where user types name of the item, sets with SeekBar time in seconds and chooses a date with custom widget. Information are saved in Realm database.

Problem is that after restarting app or adding a new item, all timers in all items restarts and start to count from the beginning. How to implement timers that would count countinously even when app won't be active or during adding a new item. Thank you in advance for help.

public class AdapterDrops extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements SwipeListener {

public static final int COUNT_FOOTER = 1;
public static final int COUNT_NO_ITEMS = 1;
public static final int ITEM = 0;
public static final int NO_ITEM = 1;
public static final int FOOTER = 2;
private final ResetListener mResetListener;
private MarkListener mMarkListener;
//inflater object which converts xml file to view object
private LayoutInflater mInflater;
public RealmResults<Drop> mResults;
private AddListener mAddListener;
private int mFilterOption;
private Realm mRealm;
private Context mContext;
Handler handler;
public long duration;


public AdapterDrops(Context context, Realm realm, RealmResults<Drop> results, AddListener listener, MarkListener markListener, ResetListener resetListener) {
    mContext = context;
    mInflater = LayoutInflater.from(context);
    update(results);
    mRealm = realm;
    mAddListener = listener;
    mMarkListener = markListener;
    mResetListener = resetListener;

}

public void update(RealmResults<Drop> results) {
    mResults = results;
    mFilterOption = AppBucketDrops.load(mContext);
    //notification do Apdapter that database was changed
    notifyDataSetChanged();

}

@Override
public long getItemId(int position) {
    if (position < mResults.size()) {
        return mResults.get(position).getAdded();
    }
    return RecyclerView.NO_ID;
}

@Override
public int getItemViewType(int position) {
    if (!mResults.isEmpty()) {
        if (position < mResults.size()) {
            return ITEM;
        } else {
            return FOOTER;
        }
    } else {
        if (mFilterOption == Filter.COMPLETE ||
                mFilterOption == Filter.INCOMPLETE) {
            if (position == 0) {
                return NO_ITEM;
            } else {
                return FOOTER;
            }
        } else {
            return ITEM;
        }
    }
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == FOOTER) {
        View view = mInflater.inflate(R.layout.footer, parent, false);
        //footerHolder class which we created below
        return new FooterHolder(view);
    } else if (viewType == NO_ITEM) {
        View view = mInflater.inflate(R.layout.no_item, parent, false);
        return new NoItemsHolder(view);
    } else {
        //layourInflater converts xml file to java View object
        View view = mInflater.inflate(R.layout.row_drop, parent, false);
        return new DropHolder(view, mMarkListener);
    }
}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    if (holder instanceof DropHolder) {
        DropHolder dropHolder = (DropHolder) holder;
        //returning an item from the paricular position
        Drop drop = mResults.get(position);
        //seting MtextView to proper drop.getWhat text
        dropHolder.setWhat(drop.getWhat());
        dropHolder.setWhen(drop.getWhen());
        dropHolder.setTimer(drop.getTimer());
        dropHolder.setBackground(drop.isCompleted());
    }

}

@Override
public int getItemCount() {
    if (!mResults.isEmpty()) {
        return mResults.size() + COUNT_FOOTER;
    } else {
        if (mFilterOption == Filter.LEAST_TIME_LEFT
                || mFilterOption == Filter.MOST_TIME_LEFT
                || mFilterOption == Filter.NONE) {
            return 0;
        } else {
            return COUNT_NO_ITEMS + COUNT_FOOTER;
        }
    }

}


@Override
public void onSwipe(int position) {
    //delete item with transaction from database
    if (position < mResults.size()) {
        mRealm.beginTransaction();
        mResults.get(position).deleteFromRealm();
        mRealm.commitTransaction();
        notifyItemRemoved(position);
    }
    resetFilterIfEmpty();
}

private void resetFilterIfEmpty() {
    if (mResults.isEmpty() && (mFilterOption == Filter.COMPLETE || mFilterOption == Filter.INCOMPLETE)) {
        mResetListener.onReset();
    }
}

public void markComplete(int position) {
    //checking that item is not a footer
    if (position < mResults.size()) {
        mRealm.beginTransaction();
        mResults.get(position).setCompleted(true);
        mRealm.commitTransaction();
        notifyItemChanged(position);
    }
}

public static class DropHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    TextView mTextWhat;
    TextView mTextWhen;
    MarkListener mMarkListener;
    Context mContext;
    View mItemView;
    TextView mTimer;
    //timer
    Handler handler;
    public long timeRemaining;
    public Drop drop;

    public DropHolder(View itemView, MarkListener listener) {
        super(itemView);
        mItemView = itemView;
        mContext = itemView.getContext();
        itemView.setOnClickListener(this);
        mTextWhat = (TextView) itemView.findViewById(R.id.tv_what);
        mTextWhen = (TextView) itemView.findViewById(R.id.tv_when);
        mTimer = (TextView) itemView.findViewById(R.id.tv_timer);
        mMarkListener = listener;

    }

    public void setWhat(String what) {
        mTextWhat.setText(what);
    }

    public Drop getDrop(Drop drop) {
        return drop;
    }

    public void setTimer(long timer) {

        handler = new Handler();
        timeRemaining = timer * 1000;
        final Runnable runnable = new Runnable() {
            @Override
            public void run() {
                timeRemaining = timeRemaining - 1000;

                if (timeRemaining > 0) {
                    handler.postDelayed(this, 1000);
                    timeRemaining = timeRemaining / 1000;
                    mTimer.setText(Long.toString(timeRemaining));
                    timeRemaining = timeRemaining * 1000;
                }
                if (timeRemaining == 0) {
                    mTimer.setText("Czas na lek !");
                }
            }
        };
        //kickstart
        handler.postDelayed(runnable, 1000);
    }

    @Override
    public void onClick(View v) {
        mMarkListener.onMark(getAdapterPosition());
    }

    public void setBackground(boolean completed) {
        Drawable drawable;
        if (completed) {
            drawable = ContextCompat.getDrawable(mContext, R.color.colorLightBlueAfterClick);
        } else {
            drawable = ContextCompat.getDrawable(mContext, R.drawable.bg_row_drop);
        }
        /*if(Build.VERSION.SDK_INT > 15){
            mItemView.setBackground(drawable);
        } else{
            mItemView.setBackgroundDrawable(drawable);
        }*/
        Util.setBackground(mItemView, drawable);

    }

    public void setWhen(long when) {
        mTextWhen.setText(DateUtils.getRelativeTimeSpanString(when, System.currentTimeMillis(), DateUtils.DAY_IN_MILLIS, 0));

    }
}

public static class NoItemsHolder extends RecyclerView.ViewHolder {

    public NoItemsHolder(View itemView) {
        super(itemView);
    }
}

public class FooterHolder extends RecyclerView.ViewHolder implements View.OnClickListener { 
    Button mBtnAdd;

    public FooterHolder(View itemView) {
        super(itemView);
        mBtnAdd = (Button) itemView.findViewById(R.id.btn_footer);
        mBtnAdd.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        //were using from this place AddListener
        mAddListener.add();
    }
}

}

Answer 1

Instead of saving the countdown time, save the end datetime (datetime now + countdown) and base the logic on that. That way when the app resets or views reset, the countdown logic will continue where it left off by comparing the datetime now with the end datetime.

Furthermore, the code you posted is posting a Runnable every second for every view, even for the ones that are not visible to the user. This causes poor performance of the app. Instead, create a single timer, possible controlled by the Activity hosting the RecyclerView.Adapter , and it'll call RecyclerView.Adapter.notifyDataSetChanged() which will in turn call RecyclerView.Adapter.onBindViewHolder() to update the UI. Hence the adapter will update all visible UI elements which means the countdown UIs (only the visible ones of course) will be updated every second too. Even when scrolling RecyclerView.Adapter.onBindViewHolder() will be called so that taken care of. This will greatly improve the performance of app when the data-set is large.