如何从适配器类中获取扩展ListFragment的活动上下文？

Question

这是我的适配器类，我想调用startActionMode。我在setActionMode方法内部调用它，但是出现以下错误：

1. 无法从Context转换为ActivityFragment。

2. 方法startActionMode（ActivityFragment.ActionModeCallback）对类型ActivityFragment未定义。

public class ListAdapter extends ArrayAdapter<ListGettersSetters>
{
    ArrayList<ListGettersSetters> arrayListGettersSetters;
    LayoutInflater layoutInflater;
    Context context;
    int Resource, i = 0, j = 0, checkedItemsCount = 0;
    Animation animation1;
    Animation animation2;
    CheckBox flipCheckBox;
    viewHolder holder;
    ActionMode actionMode;
    boolean isActionModeShowing;

    static class viewHolder
    {
        public CheckBox imageView;
        public TextView textViewName;
        public TextView textViewData;
        public TextView textViewDetails;
    }   

    public ListAdapter(Context context, int resource, ArrayList<ListGettersSetters> arrayListGettersSetters) 
    {
        super(context, resource, arrayListGettersSetters);
        this.arrayListGettersSetters = arrayListGettersSetters;
        Resource = resource;
        this.context = context;
        layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        animation1 = AnimationUtils.loadAnimation(context, R.anim.to_middle);
        animation2 = AnimationUtils.loadAnimation(context, R.anim.from_middle);

        isActionModeShowing = false;
    }

    @Override
    public int getCount() 
    {
        return arrayListGettersSetters.size();
    }

    @Override
    public ListGettersSettersgetItem(int position) 
    {
        return arrayListGettersSetters.get(position);
    }

    @Override
    public long getItemId(int position) 
    {
        return position;
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) 
    {
        holder = new viewHolder();
        if(convertView == null)
        {
            convertView = layoutInflater.inflate(Resource, null);

            holder.imageView = (CheckBox) convertView.findViewById(R.id.id_for_checkBox);
            holder.textViewName = (TextView) convertView.findViewById(R.id.id_for_name_textView);
            holder.textViewData = (TextView) convertView.findViewById(R.id.id_for_data_textView);
            holder.textViewDetails = (TextView) convertView.findViewById(R.id.id_for_details_textView);

            convertView.setTag(holder);
        }
        else
        {
            holder = (viewHolder) convertView.getTag();
        }

        holder.textViewName.setText(getItem(position).getName());
        holder.textViewData.setText(getItem(position).getData());
        holder.textViewDetails.setText(getItem(position).getDetails());
        holder.imageView.setTag(position);
        holder.imageView.setOnClickListener(new OnClickListener() 
        {
            public void onClick(View view) 
            { 
                flipCheckBox = (CheckBox) view;
                flipCheckBox.clearAnimation();
                flipCheckBox.setAnimation(animation1);
                flipCheckBox.startAnimation(animation1);
                setAnimListners(arrayListGettersSetters.get(Integer.parseInt(view.getTag().toString())));
            }
        });

        return convertView;
    }

    private void setAnimListners(final ListGettersSetters listGettersSetters)
    {
        AnimationListener animationListener = new AnimationListener()
        {
            @Override
            public void onAnimationStart(Animation animation) 
            {
                if (animation == animation1) 
                {
                    flipCheckBox.clearAnimation();
                    flipCheckBox.setAnimation(animation2);
                    flipCheckBox.startAnimation(animation2);
                } 
                else 
                {
                    listGettersSetters.setIsChecked(!listGettersSetters.isChecked());
                    setCount();
                    setActionMode();
                }
            }

            public void setCount() 
            {
                if (listGettersSetters.isChecked()) 
                {
                    checkedItemsCount++;
                } 
                else 
                {
                    if (checkedItemsCount != 0) 
                    {
                        checkedItemsCount--;
                    }
                }

                Log.v("Checked items count", checkedItemsCount + "");
            }

            private void setActionMode() 
            {
                if (checkedItemsCount > 0) 
                {
                    if (!isActionModeShowing) 
                    {
                        actionMode = ((ActivityFragment) context).startActionMode(new ActivityFragment.ActionModeCallback(context));
                        isActionModeShowing = true;
                    }
                } 
                else if (actionMode != null) 
                {
                    actionMode.finish();
                    isActionModeShowing = false;
                }

                if (actionMode != null)
                {
                    actionMode.setTitle(String.valueOf(checkedItemsCount));
                }

                notifyDataSetChanged();
            }

            @Override
            public void onAnimationRepeat(Animation animation) 
            {
            }

            @Override
            public void onAnimationEnd(Animation animation) 
            {
            }
        };
        animation1.setAnimationListener(animationListener);
        animation2.setAnimationListener(animationListener);
    }

这是我的ActivityFragment类，我在其中实现了一个名为ActionModeCallback的类，该类在我的适配器类中调用。当我在这个内部类中获取ActivityFragment的上下文时，仍然会出现相同的错误。

public class ActivityFragment extends ListFragment
{
    @Override
    public View onCreateView(LayoutInflater layoutInflater, ViewGroup viewGroup, Bundle savedInstanceState)
    {
        View view = layoutInflater.inflate(R.layout.folders_fragment_listview, null, false);

        return view;
    }

    public static final class ActionModeCallback implements ActionMode.Callback
    {   
        Context context;

        public ActionModeCallback(Context context) 
        {
            this.context = context;
        }

        @Override
        public boolean onActionItemClicked(ActionMode actionMode, MenuItem menuItem) 
        {
            Toast toast = null;
            ArrayList<FoldersFragmentGettersSetters> selectedListItems = new ArrayList<FoldersFragmentGettersSetters>();

            StringBuilder selectedItems = new StringBuilder();

            for (FoldersFragmentGettersSetters foldersFragmentGettersSetters : ((ActivityFragment ) context).listAdapter.arrayListGettersSetters) 
            {
                if (foldersFragmentGettersSetters.isChecked()) 
                {
                    selectedListItems.add(foldersFragmentGettersSetters);
                }
            }

            if (menuItem.getTitle().equals("Delete")) 
            {
                toast = Toast.makeText(context, "Delete: " + selectedItems.toString(), Toast.LENGTH_SHORT);
            } 
            else if (menuItem.getTitle().equals("Archive")) 
            {
                toast = Toast.makeText(context, "Archive: " + selectedItems.toString(), Toast.LENGTH_SHORT);
            } 
            else if (menuItem.getTitle().equals("Mark unread")) 
            {
                toast = Toast.makeText(context, "Mark unread: " + selectedItems.toString(), Toast.LENGTH_SHORT);
            } 
            else if (menuItem.getTitle().equals("Move")) 
            {
                toast = Toast.makeText(context, "Move: " + selectedItems.toString(), Toast.LENGTH_SHORT);
            } 
            else if (menuItem.getTitle().equals("Remove star")) 
            {
                toast = Toast.makeText(context, "Remove star: " + selectedItems.toString(), Toast.LENGTH_SHORT);
            }
            if (toast != null) 
            {
                toast.show();
            }
            actionMode.finish();
            return true;
        }

        @Override
        public boolean onCreateActionMode(ActionMode actionMode, Menu menu) 
        {
            menu.add("Delete").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
            menu.add("Archive").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
            menu.add("Mark unread").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
            menu.add("Move").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
            menu.add("Remove star").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);

            return true;
        }

        @Override
        public void onDestroyActionMode(ActionMode actionMode) 
        {
            ((ActivityFragment ) context).inboxAdapter.checkedItemsCount = 0;
            ((ActivityFragment ) context).inboxAdapter.isActionModeShowing = false;
            for (FoldersFragmentGettersSetters foldersFragmentGettersSettersItem : ((InboxFragment) context).inboxList) 
            {
                foldersFragmentGettersSettersItem.setIsChecked(false);
            }
            ((ActivityFragment ) context).listAdapter.notifyDataSetChanged();

            Toast.makeText(context, "Action mode closed", Toast.LENGTH_SHORT).show();
        }

        @Override
        public boolean onPrepareActionMode(ActionMode actionMode, Menu menu) 
        {       
            return false;
        }
    }
}

- Ashish Kumar Gupta

Answer 1

将您的ListAdapter构造函数修改为

public ListAdapter(Context context, int resource, ArrayList<ListGettersSetters> arrayListGettersSetters) 

to

public ListAdapter(ActivityFragment context, int resource, ArrayList<ListGettersSetters> arrayListGettersSetters)

- Pankaj Deshpande

---

它说构造函数未定义。 - Ashish Kumar Gupta

尝试通过将活动转换为(ActivityFragment).this作为第一个参数来调用它。 - Pankaj Deshpande

我在super()和(Context)activityContext处分别遇到了这些错误。"Cannot refer to 'this' nor 'super' while explicitly invoking a constructor" & "Cannot cast from ActivityFragment to Context" - Ashish Kumar Gupta

我已经发布了我整个代码，即ActivityFragment.java和ListAdapter.java。 - Ashish Kumar Gupta

你的ActionModeCallBack类中以下代码行有问题吗？ for (FoldersFragmentGettersSetters foldersFragmentGettersSetters : ((ActivityFragment ) context).listAdapter.arrayListGettersSetters) - Pankaj Deshpande

Answer 2

一个好的方法是使用回调函数。

1. 在你的适配器类中创建回调接口（监听器）。
2. 声明接口的实例变量，例如 startActionModeCallback。
3. 在适配器构造函数中，传递监听器对象并将其赋值给 startActionModeCallback。
4. 当你在 ActivityFragment 中创建适配器实例时，将其作为监听器传递，并在片段中实现其回调方法。
5. 在你的适配器中的任何地方调用回调方法，它将被片段监听。

希望这对你有意义。如果需要澄清，请随时问我。祝你好运！

---

示例

适配器类

public class ListAdapter extends ArrayAdapter<ListGettersSetters>
{

Interface StartActionInterface
{
public void startActionMode();
}


//declare other instance variables and add following

StartActionInterface startActionModeListener;

//change your constructor as:

public ListAdapter(Context context, int resource, ArrayList<ListGettersSetters> arrayListGettersSetters, StartActionInterface listener) 
{
//normal code
startActionModeListener = listener;
}

}

ActivityFragment

public class ActivityFragment extends ListFragment implements StartActionInterface
{
    @Override
    public View onCreateView(LayoutInflater layoutInflater, ViewGroup viewGroup, Bundle savedInstanceState)
    {
        View view = layoutInflater.inflate(R.layout.folders_fragment_listview, null, false);

////////initialize adapter and pass `this` in last argument

        return view;
    }

//Implement callback method. Also implement `setActionMode()` method here in fragment. 

void startActionMode()
{
setActionMode();
}

}

在函数 setActionMode() 中，替换以下行：

 if (!isActionModeShowing) 
 {
    actionMode = ((ActivityFragment) context).startActionMode(new ActivityFragment.ActionModeCallback(context));
                        isActionModeShowing = true;
  }

使用：

if (!isActionModeShowing) 
{
    actionMode = getActivity().startActionMode(new ActionModeCallback(getActivity()));
                        isActionModeShowing = true;
}

- NightFury