关闭应用程序或切换碎片时，将所选项目保存在RecyclerView中

Question

我的片段中有一个Recycler View，它在单击项目时打开活动，并在长时间单击项目时高亮显示该项目。但是，当我切换片段或关闭应用程序并重新打开它时，我希望以前选择的项目保持选中状态。我想这是用Shared Preferences完成的，但如何保存所选项目，然后再次填充？

这是我的自定义适配器。TextViews在onBindViewHolder:中选择

public class ExampleAdapter extends RecyclerView.Adapter<ExampleAdapter.ExampleViewHolder> {
private ArrayList<Workout> mExampleList;
private OnItemClickListener mListener;
public interface OnItemClickListener {
void onItemClick(int position);
}
public void setOnItemClickListener(OnItemClickListener listener) {
mListener = listener;
}
public static class ExampleViewHolder extends RecyclerView.ViewHolder {
public TextView mTextView1,mTextView2,mTextView3,mTextView4;
CardView mCardView;
public ExampleViewHolder(View itemView, final OnItemClickListener listener) 
{
super(itemView);
mTextView1 = itemView.findViewById(R.id.listTextView1);
mTextView2 = itemView.findViewById(R.id.listTextView2);
mTextView3 = itemView.findViewById(R.id.listTextView3);
mTextView4 = itemView.findViewById(R.id.listTextView4);
mCardView = itemView.findViewById(R.id.cardView);
itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(listener != null) {
int position = getAdapterPosition();
if (position != RecyclerView.NO_POSITION) {
listener.onItemClick(position);
}
}
}
});
}
}
public ExampleAdapter(ArrayList<Workout> exampleList) {
mExampleList = exampleList;
}
@NonNull
@Override
public ExampleViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_view_item,parent,false);
ExampleViewHolder evh = new ExampleViewHolder(v, mListener);
return evh;
}
@Override
public void onBindViewHolder(@NonNull final ExampleViewHolder holder, final int position) {
Workout workout = mExampleList.get(position);
holder.mTextView1.setText(workout.getText1());
holder.mTextView2.setText(workout.getText2());
holder.mTextView3.setText(workout.getText3());
holder.mTextView4.setText(workout.getText4());
holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View view) {
if(holder.mTextView1.isSelected()) {
holder.mTextView1.setSelected(false);
holder.mTextView2.setSelected(false);
holder.mTextView3.setSelected(false);
holder.mTextView4.setSelected(false);
} else {
holder.mTextView1.setSelected(true);
holder.mTextView2.setSelected(true);
holder.mTextView3.setSelected(true);
holder.mTextView4.setSelected(true);
}
return true;
}
});
}
@Override
public int getItemCount() {
return mExampleList.size();
}
}

这是我的片段：

public class HomeFragment extends Fragment implements View.OnClickListener{
private RecyclerView mRecyclerView;
private ExampleAdapter mAdapter;
private RecyclerView.LayoutManager mLayoutManager;
ArrayList<Workout> exampleList;
MainActivity mainActivity;
DataModel dataModel = new DataModel();
View rootView;
private TextView[] textViews;
private CardView[] cardViews;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_home,container,false);
mainActivity = (MainActivity) getActivity();
mainActivity.setToolbarName("Workouts");
textViews = new TextView[16];
cardViews = new CardView[3];
for(int i=0; i<textViews.length; i++) {
{
String buttonID = "textView" + (i+1);
int resID = getResources().getIdentifier(buttonID, "id", getActivity().getPackageName());
textViews[i] = ((TextView) rootView.findViewById(resID));
}
}
updateWeekText();
textViews[2].setText(roundDecimals(mainActivity.getBenchMax()));
textViews[4].setText(roundDecimals(mainActivity.getSquatMax()));
textViews[6].setText(roundDecimals(mainActivity.getDeadliftMax()));
textViews[8].setText(roundDecimals(mainActivity.getPressMax()));
Button buttonNextWeek = rootView.findViewById(R.id.buttonNextWeek);
buttonNextWeek.setOnClickListener(this);
int week = MainActivity.getWeekNumber();
exampleList = new ArrayList<>();
if(week == 1 || week == 2 || week == 3 || week == 4){
exampleList.add(new Workout("Day 1", "C-S", "C-B", "Rack Pulls"));
exampleList.add(new Workout("Day 2", "2ct Paused Squat", "C-P", "Pendlay Row"));
exampleList.add(new Workout("Day 3", "C-D", "Floor Press", "Leg Press"));
} else {
exampleList.add(new Workout("Day 1", "C-S", "C-B", "2ct Paused Deadlift"));
exampleList.add(new Workout("Day 2", "Pin Squat", "C-P", "Pendlay Row"));
exampleList.add(new Workout("Day 3", "C-D", "2ct Paused Bench", "303 Tempo Squat"));
}
buildRecyclerView();
return rootView;
}
public void buildRecyclerView() {
mRecyclerView = rootView.findViewById(R.id.recyclerView);
mRecyclerView.setHasFixedSize(true);
mLayoutManager = new LinearLayoutManager(getContext());
mAdapter = new ExampleAdapter(exampleList);
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.setAdapter(mAdapter);
mAdapter.setOnItemClickListener(new ExampleAdapter.OnItemClickListener() {
@Override
public void onItemClick(int position) {
if (position == 0) {
startActivity(new Intent(getActivity(),ActivityDay1.class));
}
if (position == 1) {
startActivity(new Intent(getActivity(),ActivityDay2.class));
}
}
});
}
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.buttonNextWeek:
createDialog();
break;
}
}
private void updateWeekText() {
textViews[9].setText("Current week: "+String.valueOf(mainActivity.getWeekNumber()));
}
private void createDialog(){
int nextWeek = mainActivity.getWeekNumber()+1;
AlertDialog.Builder builder;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
builder = new AlertDialog.Builder(getContext(), android.R.style.Theme_Material_Dialog_Alert);
} else {
builder = new AlertDialog.Builder(getContext());
}
builder.setTitle("Start week "+nextWeek+"?")
.setMessage("Are you sure?")
.setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
mainActivity.setWeekNumber(mainActivity.getWeekNumber()+1);
updateWeekText();
}
})
.setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// do nothing
}
})
.setIcon(R.drawable.ic_navigate_next_black_24dp)
.show();
}
public String roundDecimals(double a){
NumberFormat nf = new DecimalFormat("##.###");
return nf.format(a);
}

我将感谢任何帮助
如果需要更多的代码，请告诉我。

Answer 1

您需要首先修复Adapter实现中的一些错误。

将isCompleted布尔字段添加到Workout类中。对于当前的适配器实现，仅仅通过滚动recyclerView，您的"选定"状态就会变得一团糟，因为您不存储值，只更改ViewHolder状态。

将LongLickListener的主体移动到ViewHolder:的新方法中

void setSelected(boolean selected){
mTextView1.setSelected(selected);
mTextView2.setSelected(selected);
mTextView3.setSelected(selected);
mTextView4.setSelected(selected);
}

现在您可以将LongClickListener更改为：

@Override
public boolean onLongClick(View view) {
workout.isCompleted = !workout.isCompleted;
holder.setSelected(workout.isCompleted);
return true;
}

通过这种方式，训练完成的状态实际上存储在您的数据列表中。为了确保视图状态正确，请将此行添加到onBindViewHolder:

holder.setSelected(workout.isCompleted);

否则，先前绑定到"已完成"训练的ViewHolder将在显示"未完成"训练时错误显示。

至于存储所选项目，这有点棘手，因为这主要是一个持久性/数据库设计问题。

• 你的Workout项目只是锻炼的定义吗
• 它们重复出现了吗
• 用户可以添加/删除锻炼定义吗
• 有完成训练的历史吗？还是每天重置

您至少需要为每次训练定义一些稳定的ID才能正确地保持它们，然后我建议研究使用原始SQLite、Room或Realm的数据库实现。