Question

我正在使用backbutton作为活动的界面，但是它对我来说无法正常工作，因为在backpress上显示arraylist的大小为0

//这是我从中获得后退按钮界面的活动类。

 public class Multiple_Images extends AppCompatActivity {


@Override
public void onBackPressed() {
        if(twice ==true){

         Intent intent =new Intent(this,MainActivity.class);
          startActivity(intent);
                           }ImageAdapter imageAdapter =new ImageAdapter(this);
      imageAdapter.onBackPress();
  Toast.makeText(this, "Press twice", Toast.LENGTH_SHORT).show();
    twice =true;
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {

            twice =false; }   }, 2000); }}

///这是我正在使用后退按钮的适配器类

public class ImageAdapter extends BaseAdapter implements onBackPressListener {
    ArrayList<String> selectedArraylist ;
    @Override
    public boolean onBackPress() {

        selectedArraylist.clear();

        Toast.makeText(context, "All values unselected", Toast.LENGTH_SHORT).show();

        return true;
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        urimodel=new ArrayList<>();

        final ImageView imageGrid ;
        Activity activity = (Activity) context;
        actionMode = activity.startActionMode(new Actionmode());

        final GridModel gridModel=(GridModel) this.getItem(i);

        if(view==null) {
            view = LayoutInflater.from(context).inflate(R.layout.model, null);
            selectedArraylist    =new ArrayList<>();
        }

        final CardView cardView=   (CardView)view.findViewById(R.id.cardview_image);
        imageGrid = (ImageView) view.findViewById(R.id.grid_image);
        //   gridText = (TextView) view.findViewById(R.id.grid_text);

        imageGrid.setScaleType(ImageView.ScaleType.CENTER_CROP);
        //  imageGrid.setScaleType(ImageView.ScaleType.CENTER_CROP);

        Picasso.get().load(gridModel.getImage()).resize(200,200).into(imageGrid);

        if (selectedArraylist.contains(gridModel.getImage_text())) {

            cardView.setCardBackgroundColor(CARD_SELECTED_COLOR);

        }else {

            cardView.setCardBackgroundColor(Color.WHITE);
        }
        return view;
    }
}

Answer 1

您可以在onBackPressed

内完成此操作

@Override
public void onBackPressed() {

    if (twice == true) {

        super.onBackPressed(); //this backs to the previous activity, if you want to stay with Intent, add finish() after startActivity()
        return;
    } else {

        for (int i = 0; i < list.size(); i++) {

            if (gridView.isItemChecked(i)) {

                gridView.setItemChecked(i, false);
            }
        }
        //selectedArraylist.clear(); this is clearing your array of selected items
    }
    twice = true;
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {

            twice = false;
        }
    }, 2000);
}

我不知道，为什么将selectedArraylist =new ArrayList<>();放在适配器getView()方法中。每次膨胀新的列表项时，都会触发getView（），这意味着每次更改适配器源，滚动列表时，都会调用此方法，并且每次初始化数组时，内部的所有数据都会丢失。您应该像对待显示项目的工具那样对待适配器类，并且上述所有操作都将在外部适配器上进行。

Answer 2

非常容易，我给您我自己的项目代码，希望对您有所帮助。

StudentFragment.java：

private void MultiSelected_Student(int position) {
    Student data = adapter_class.getItem(position);
    if (data != null) {
        if (selectedIds.contains(data)) selectedIds.remove(data);
        else selectedIds.add(data);
    }
}

private void Remove_MultiSelected() {
    try {
        selectedIds.clear();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

public void Group_UnSelect() {
    Remove_MultiSelected();
    MultiSelected = false;
    fab.setVisibility(View.GONE);
    homeeActivity.studentsMultiSelect = false;
    notifyy();
}

private void notifyy() {
    adapter_class.notifyDataSetChanged();
}

HomeActivity.java：

public boolean studentsMultiSelect = false;

@Override
public void onBackPressed() {
    if (studentsMultiSelect) {
        studentFragment.Group_UnSelect();
    } else {
        super.onBackPressed();
    }
}

如何使用后退按钮取消选择网格视图中的所有项目？

2 个答案: