Fehler beim Speichern des aktivierten Kontrollkästchens in der benutzerdefinierten Listenansicht

Question

Ich möchte den aktivierten Status des Kontrollkästchens in meiner Listenansicht speichern, damit die ausgewählten Checkoxen ausgewählt bleiben, wenn ich zu einer anderen Aktivität gehe und dann zu dieser Aktivität zurückkomme. Ich habe einen benutzerdefinierten Adapter verwendet, um 2 Arten von Layout anzuzeigen. Ich habe sparsebooleanray und sharedpreference verwendet, um den aktivierten Status zu speichern. Dies funktioniert bei der Verwendung von List, aber ich bekomme NullPointerException, wenn ich List verwende. Gibt es eine Möglichkeit, den Staat hier zu retten?

public class ListViewActivity extends AppCompatActivity { 

    SharedPreferences sharedPreferences; 
    ListView listView; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_list_view); 

     listView = (ListView) findViewById(R.id.listview); 

     List<Item> items = new ArrayList<>(); 
     for (int i = 1; i <= 10; i++) { 
      items.add(new Item("I am TextView layout #" + i, Item.TYPE_TEXTVIEW, false)); 
      items.add(new Item("I am ImageView layout #" + i, Item.TYPE_IMAGEVIEW, false)); 
     } 

     MultipleLayoutAdapter adapter = new MultipleLayoutAdapter(this, items); 
     listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE); 
     listView.setAdapter(adapter); 

     sharedPreferences = getSharedPreferences("MySharedPrefs", Context.MODE_PRIVATE); 



     Set<String> checkedItemsSource = sharedPreferences.getStringSet("checked_items", new HashSet<String>()); 
     SparseBooleanArray checkedItems = convertToCheckedItems(checkedItemsSource); 
     for (int i = 0; i < checkedItems.size(); i++) { 
      int checkedPosition = checkedItems.keyAt(i); 
      listView.setItemChecked(checkedPosition, true); 
     } 
    } 


    @Override 
    protected void onDestroy() { 
     super.onDestroy(); 
     SparseBooleanArray checkedItems = listView.getCheckedItemPositions(); 
////got exception here 
     Set<String> stringSet = convertToStringSet(checkedItems); 
     sharedPreferences.edit() 
       .putStringSet("checked_items", stringSet) 
       .apply(); 
    } 

    private SparseBooleanArray convertToCheckedItems(Set<String> checkedItems) { 
     SparseBooleanArray array = new SparseBooleanArray(); 
     for(String itemPositionStr : checkedItems) { 
      int position = Integer.parseInt(itemPositionStr); 
      array.put(position, true); 
     } 

     return array; 
    } 

    private Set<String> convertToStringSet(SparseBooleanArray checkedItems) { 
     Set<String> result = new HashSet<>(); 
////got exception here 
     for (int i = 0; i < checkedItems.size(); i++) { 
      result.add(String.valueOf(checkedItems.keyAt(i))); 
     } 

     return result; 
    } 
} 


public class MultipleLayoutAdapter extends BaseAdapter { 

    private Context context; 
    private List<Item> items; 

    public MultipleLayoutAdapter(Context context, List<Item> items) { 
     this.context = context; 
     this.items = new ArrayList<>(items); 
    } 

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

    @Override 
    public Item getItem(int position) { 
     return items.get(position); 
    } 

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

    @Override 
    public int getViewTypeCount() { 
     return 2; 
    } 

    @Override 
    public int getItemViewType(int position) { 
     return getItem(position).getType(); 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
     Item item = getItem(position); 
     int viewType = getItemViewType(position); 
     switch (viewType) { 

      case Item.TYPE_TEXTVIEW: 
       convertView = inflateTextView(convertView, parent, item); 
       break; 

      case Item.TYPE_IMAGEVIEW: 
       convertView = inflateImageView(convertView, parent, item); 
       break; 
     } 
     return convertView; 
    } 


    private View inflateTextView(View convertView, ViewGroup parent, Item item) { 
     TextViewHolder viewHolder; 
     if (convertView == null) { 
      convertView = LayoutInflater.from(context).inflate(R.layout.textview_list_row, parent, false); 
      viewHolder = new TextViewHolder(convertView); 
      convertView.setTag(viewHolder); 
     } 
     else { 
      viewHolder = (TextViewHolder) convertView.getTag(); 
     } 

     viewHolder.textView.setText(item.getData()); 
     viewHolder.checkBox.setChecked(item.isBox()); 

     return convertView; 
    } 

    private View inflateImageView(View convertView, ViewGroup parent, Item item) { 
     ImageViewHolder viewHolder; 
     if (convertView == null) { 
      convertView = LayoutInflater.from(context).inflate(R.layout.imageview_list_row, parent, false); 
      viewHolder = new ImageViewHolder(convertView); 
      convertView.setTag(viewHolder); 
     } 
     else { 
      viewHolder = (ImageViewHolder) convertView.getTag(); 
     } 

     viewHolder.textView.setText(item.getData()); 
     viewHolder.checkBox.setChecked(item.isBox()); 


     return convertView; 
    } 




    static class TextViewHolder { 
     private TextView textView; 
     private CheckBox checkBox; 

     public TextViewHolder(View convertView) { 
      this.textView = (TextView) convertView.findViewById(R.id.textview); 
      this.checkBox = (CheckBox) convertView.findViewById(R.id.checkbox); 
     } 
    } 

    static class ImageViewHolder { 
     private ImageView imageView; 
     private TextView textView; 
     private CheckBox checkBox; 

     public ImageViewHolder(View convertView) { 
      this.imageView = (ImageView) convertView.findViewById(R.id.imageview); 
      this.textView = (TextView) convertView.findViewById(R.id.textview); 
      this.checkBox = (CheckBox) convertView.findViewById(R.id.checkbox); 
     } 
    } 

} 

public class Item { 
    public static final int TYPE_TEXTVIEW = 0; 
    public static final int TYPE_IMAGEVIEW = 1; 

    private String data; 
    private int type; 
    private boolean box; 
    private Context context; 

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

    public Item(String data, int type, boolean box) { 
     this.data = data; 
     this.type = type; 
     this.box = box; 
    } 

    public String getData() { 
     return data; 
    } 

    public int getType() { 
     return type; 
    } 

    public boolean isBox() { 
     return box; 
    } 

    public void setBox(boolean box) { 
     this.box = box; 
    } 
} 

Answer 1

Wenn wir grep code gehen, werden wir sehen:

public SparseBooleanArray More ...getCheckedItemPositions() { 
    if (mChoiceMode != CHOICE_MODE_NONE) { 
     return mCheckStates; 
    } 
    return null; 
} 

Und wir erinnern uns, dass Sie null empfangen, wenn listView.getCheckedItemPositions() aufrufen. Also ich denke es könnte sein, weil du listView.setChoiceMode nicht benutzt hast.

Answer 2

MultipleLayoutAdapter

public class MultipleLayoutAdapter extends BaseAdapter { 

private Context context; 
private List<Item> items; 

public MultipleLayoutAdapter(Context context, List<Item> items) { 
    this.context = context; 
    this.items = new ArrayList<>(items); 
} 

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

@Override 
public Item getItem(int position) { 
    return items.get(position); 
} 

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

@Override 
public int getViewTypeCount() { 
    return 2; 
} 

@Override 
public int getItemViewType(int position) { 
    return getItem(position).getType(); 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    Item item = getItem(position); 
    int viewType = getItemViewType(position); 
    switch (viewType) { 

     case Item.TYPE_TEXTVIEW: 
      convertView = inflateTextView(convertView, parent, item); 
      break; 

     case Item.TYPE_IMAGEVIEW: 
      convertView = inflateImageView(convertView, parent, item); 
      break; 
    } 
    return convertView; 
} 


private View inflateTextView(View convertView, ViewGroup parent, final Item item) { 
    TextViewHolder viewHolder; 
    if (convertView == null) { 
     convertView = LayoutInflater.from(context).inflate(R.layout.textview_list_row, parent, false); 
     viewHolder = new TextViewHolder(convertView); 
     convertView.setTag(viewHolder); 
    } 
    else { 
     viewHolder = (TextViewHolder) convertView.getTag(); 
    } 

    viewHolder.textView.setText(item.getData()); 

    viewHolder.checkBox.setOnCheckedChangeListener(null); 
    viewHolder.checkBox.setChecked(item.isBox()); 
    viewHolder.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() { 
     @Override 
     public void onCheckedChanged(CompoundButton compoundButton, boolean b) { 
      item.setBox(b); 
     } 
    }); 

    return convertView; 
} 

private View inflateImageView(View convertView, ViewGroup parent, final Item item) { 
    ImageViewHolder viewHolder; 
    if (convertView == null) { 
     convertView = LayoutInflater.from(context).inflate(R.layout.imageview_list_row, parent, false); 
     viewHolder = new ImageViewHolder(convertView); 
     convertView.setTag(viewHolder); 
    } 
    else { 
     viewHolder = (ImageViewHolder) convertView.getTag(); 
    } 

    viewHolder.textView.setText(item.getData()); 

    viewHolder.checkBox.setOnCheckedChangeListener(null); 
    viewHolder.checkBox.setChecked(item.isBox()); 
    viewHolder.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() { 
     @Override 
     public void onCheckedChanged(CompoundButton compoundButton, boolean b) { 
      item.setBox(b); 
     } 
    }); 


    return convertView; 
} 




static class TextViewHolder { 
    private TextView textView; 
    private CheckBox checkBox; 

    public TextViewHolder(View convertView) { 
     this.textView = (TextView) convertView.findViewById(R.id.textview); 
     this.checkBox = (CheckBox) convertView.findViewById(R.id.checkbox); 
    } 
} 

static class ImageViewHolder { 
    private ImageView imageView; 
    private TextView textView; 
    private CheckBox checkBox; 

    public ImageViewHolder(View convertView) { 
     this.imageView = (ImageView) convertView.findViewById(R.id.imageview); 
     this.textView = (TextView) convertView.findViewById(R.id.textview); 
     this.checkBox = (CheckBox) convertView.findViewById(R.id.checkbox); 
    } 
} 

} 

MainActivity

public class MainActivity extends AppCompatActivity { 

SharedPreferences sharedPreferences; 
ListView listView; 
List<Item> items = new ArrayList<>(); 
MultipleLayoutAdapter adapter; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    listView = (ListView) findViewById(R.id.listview); 

    for (int i = 1; i <= 10; i++) { 
     items.add(new Item("I am TextView layout #" + i, Item.TYPE_TEXTVIEW, false)); 
     items.add(new Item("I am ImageView layout #" + i, Item.TYPE_IMAGEVIEW, false)); 
    } 

    findViewById(R.id.btn_go).setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      startActivity(new Intent(MainActivity.this, Main2Activity.class)); 
     } 
    }); 
} 

@Override 
protected void onResume() { 
    super.onResume(); 

    sharedPreferences = getSharedPreferences("MySharedPrefs", Context.MODE_PRIVATE); 
    Set<String> checkedItemsSource = sharedPreferences.getStringSet("checked_items", new HashSet<String>()); 
    SparseBooleanArray checkedItems = convertToCheckedItems(checkedItemsSource); 

    for (int i = 0; i < checkedItems.size(); i++) { 
     int checkedPosition = checkedItems.keyAt(i); 
     items.get(checkedPosition).setBox(true); 
    } 

    if (adapter == null) { 
     adapter = new MultipleLayoutAdapter(this, items); 
     listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE); 
     listView.setAdapter(adapter); 
    } else { 
     adapter.notifyDataSetChanged(); 
    } 
} 

@Override 
protected void onPause() { 
    Set<String> stringSet = new HashSet<>(); 
    for (int i = 0; i < items.size(); i++) { 
     if (items.get(i).isBox()) { 
      stringSet.add(String.valueOf(i)); 
     } 
    } 

    sharedPreferences.edit() 
      .putStringSet("checked_items", stringSet) 
      .apply(); 

    super.onPause(); 
} 

private SparseBooleanArray convertToCheckedItems(Set<String> checkedItems) { 
    SparseBooleanArray array = new SparseBooleanArray(); 
    for (String itemPositionStr : checkedItems) { 
     int position = Integer.parseInt(itemPositionStr); 
     array.put(position, true); 
    } 

    return array; 
} 

private Set<String> convertToStringSet(SparseBooleanArray checkedItems) { 
    Set<String> result = new HashSet<>(); 
    for (int i = 0; i < checkedItems.size(); i++) { 
     result.add(String.valueOf(checkedItems.keyAt(i))); 
    } 

    return result; 
} 
}