如何使用后退按钮取消选择网格视图中的所有项目?

Question

我正在使用后退按钮作为活动的界面，但它对我来说无法正常工作，因为在反向按下时显示 0 大小的 arraylist

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); }}

这里 是适配器类 我正在使用后退按钮

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

简单地说，你可以在里面做onBackPressed

@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，你为什么要把selectedArraylist =new ArrayList<>();放在适配器getView()方法中。 getView(( 每次都会触发，当一个新的列表项膨胀时，这意味着每次当你更改适配器源时，滚动列表调用此方法，每次初始化数组时，里面的所有数据都会丢失。您应该将适配器类视为显示项的工具，并且上述所有操作都使外部适配器。

Answer 2

很容易， 我给你我自己的项目代码，希望对你有帮助。

学生片段.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();
}

首页活动.java：

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