我正在使用 ListView 的自定义适配器来显示图像和标题。
在我的应用程序中,我添加和删除列表中的项目,并且必须在界面上显示更改。
关于数据的任何更改,我将从数据库中获取所有列表,并将其存储在适配器列表中,然后调用adapter.notifyDataSetChanged();。但界面未显示任何更改。
另一方面,当我直接从适配器添加或删除项目时,它会正确响应。
我已经使用了简单的适配器,并为此适配器。工作正常,但对于自定义而言,它没有响应。
我也尝试过许多关于stackoverflow的解决方案,但都不起作用。
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我这样做
在oncreate

enter code here

            product_data = new ArrayList<Product>();
    Bundle extras = getIntent().getExtras();
    if (extras != null) {
        value = extras.getInt("list_id");
    }
    product_data = db.getAllProductsstatus(value, 1);
    Collections.reverse(product_data);

    adapter = new ProductAdopter(this,
            R.layout.listview_item_row, product_data, 2);
    ListView listView1 = (ListView)findViewById(R.id.listView1);
    listView1.setAdapter(adapter);
    registerForContextMenu(listView1);

并在onMenuItemSelected中
enter code here
@Override
public boolean onMenuItemSelected(int featureId, MenuItem item) {
    AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo)item.getMenuInfo();

      int menuItemIndex = item.getItemId();
      String listItemName = adapter.getItem(info.position)._name;
      int id = adapter.getItem(info.position)._id;

         if(menuItemIndex == 0)
        {

            db.deleteProduct(adapter.getItem(info.position));

            product_data = db.getAllProducts(value);
            Collections.reverse(product_data);
            //adapter.remove(adapter.getItem(info.position));
            adapter.notifyDataSetChanged();
        }
        else if(menuItemIndex == 1){
            String name ;
            if (adapter.getItem(info.position)._status == 0){
                popall("bar code", "no bar code entered");
            }
            else {
            popall("bar code", adapter.getItem(info.position)._bar_code);
            }
        }
        else if (menuItemIndex == 2){
            adapter.getItem(info.position)._status = 0;
            adapter.getItem(info.position)._bar_code = "0";
            db.updateProduct(adapter.getItem(info.position));
                product_data = db.getAllProductsstatus(value, 1);
            adapter.notifyDataSetChanged();

            popall("alert", "successfully done");
        }
      return true;
}

我的自定义适配器类如下
public class ProductAdopter extends ArrayAdapter<Product> {
    Context context;
    int layoutResourceId;
    List<Product> data = null;
    int source;
    public ProductAdopter(Context context, int layoutResourceId, List<Product> product_data, int source) {
        // TODO Auto-generated constructor stub
        super(context, layoutResourceId, product_data);
        this.layoutResourceId = layoutResourceId;
        this.context = context;
        this.data = product_data;
        this.source = source;
    }
   // public ProductAdopter(MainActivity context2, int listviewItemRow, List<Product> product_data) {
        // TODO Auto-generated constructor stub
    //}
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View row = convertView;
        ProductHolder holder = null;

        if(row == null && source == 1)
        {
            LayoutInflater inflater = ((MainActivity)context).getLayoutInflater();
            row = inflater.inflate(layoutResourceId, parent, false);

            holder = new ProductHolder();
            holder.imgIcon = (ImageView)row.findViewById(R.id.imgIcon);
            holder.txtTitle = (TextView)row.findViewById(R.id.txtTitle);

            row.setTag(holder);
        }
        if(row == null && source == 2)
        {
            LayoutInflater inflater = ((purchased)context).getLayoutInflater();
            row = inflater.inflate(layoutResourceId, parent, false);

            holder = new ProductHolder();
            holder.imgIcon = (ImageView)row.findViewById(R.id.imgIcon);
            holder.txtTitle = (TextView)row.findViewById(R.id.txtTitle);

            row.setTag(holder);
        }
        if(row == null && source == 3)
        {
            LayoutInflater inflater = ((Skiped)context).getLayoutInflater();
            row = inflater.inflate(layoutResourceId, parent, false);

            holder = new ProductHolder();
            holder.imgIcon = (ImageView)row.findViewById(R.id.imgIcon);
            holder.txtTitle = (TextView)row.findViewById(R.id.txtTitle);

            row.setTag(holder);
        }


        else
        {
            holder = (ProductHolder)row.getTag();
        }

        Product product = data.get(position);
        holder.txtTitle.setText(product.getName());
        if(product.icon.equals("no")){
            holder.imgIcon.setImageResource(R.drawable.blank);
        }
        else{
            File imgFile = new  File(product.icon);
            if(imgFile.exists()){

                Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());
                Bitmap resized = Bitmap.createScaledBitmap(myBitmap, 70, 70, true);

                holder.imgIcon.setImageBitmap(resized);
                myBitmap.recycle();
            }
        }

        return row;
    }
    static class ProductHolder
    {
        ImageView imgIcon;
        TextView txtTitle;
    }

}

最佳答案

问题是,在您的onMenuItemSelected()中,您具有以下这一行:

product_data = db.getAllProducts(value);

当使用onCreate()创建适配器时,您给它提供了对product_data的引用。那时,您对product_data所做的更改将传播到适配器中,因为它具有对列表的引用。

但是,一旦您为product_data变量分配了一个新列表(就像在onMenuItemSelected()中所做的那样),适配器现在就引用了旧列表,而product_data现在指向了一个新列表。因此,您的适配器不知道新列表中的更改。

与其重新分配变量,不如尝试清除它并复制项目,如下所示:
product_data.clear();
product_data.addAll(db.getAllProducts(value));

另一方面,如果您从数据库中读取数据,则应考虑改用CursorAdapter

这是一个简单的教程:
http://blog.cluepusher.dk/2009/11/16/creating-a-custom-cursoradapter-for-android/

10-07 19:20
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