android - 除非滚动，否则 ListView 图像不会改变

Question

我有一个 ListView 。单击列表项时，它会打开一个新 Activity ，其中包含一个按钮(添加到收藏夹)，该按钮将打开的列表项添加到我的收藏夹 Activity (使用共享首选项)，并且应该将列表项中心脏图像的颜色从灰色更改为红色，表示它在收藏夹中。 将列表项添加到收藏夹工作正常，但心脏图像不会从灰色变为红色，除非它从屏幕上滚出用户 View 并再次滚动回它。 为了更好地理解我的问题 look at this video

我想瞬间改变图像

顺便说一下，将 listitem 对象转换为 jsonString 并通过 intent 传递它，我使用了 jacksons 库

我使用的代码

我的列表 fragment 的 onitemclicklistener

@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
                        long id) {

                            ObjectMapper mapper = new ObjectMapper();
                            Product pro = productListAdapter.getItem(position);


    try
    {


        String jsonInString = mapper.writeValueAsString(pro);

        Intent intent = new Intent(activity.getApplicationContext(), SingleItemView.class);
        intent.putExtra("selected item", jsonInString);


        startActivity(intent);
    }
    catch (JsonProcessingException e)
    {}  



}

我的列表适配器

public class ProductListAdapter extends ArrayAdapter<Product> {

private Context context;
List<Product> products;
SharedPreference sharedPreference;

public ProductListAdapter(Context context, List<Product> products) {
    super(context, R.layout.product_list_item, products);
    this.context = context;
    this.products = products;
    sharedPreference = new SharedPreference();
}

private class ViewHolder {
    TextView productNameTxt;
    TextView productDescTxt;
    TextView productPriceTxt;
    ImageView favoriteImg;
}

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

@Override
public Product getItem(int position) {
    return products.get(position);
}

@Override
public long getItemId(int position) {
    return 0;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder = null;
    if (convertView == null) {
        LayoutInflater inflater = (LayoutInflater) context
            .getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.product_list_item, null);
        holder = new ViewHolder();
        holder.productNameTxt = (TextView) convertView
            .findViewById(R.id.txt_pdt_name);
        holder.productDescTxt = (TextView) convertView
            .findViewById(R.id.txt_pdt_desc);
        holder.productPriceTxt = (TextView) convertView
            .findViewById(R.id.txt_pdt_price);
        holder.favoriteImg = (ImageView) convertView
            .findViewById(R.id.imgbtn_favorite);

        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    Product product = (Product) getItem(position);
    holder.productNameTxt.setText(product.getName());
    holder.productDescTxt.setText(product.getDescription());
    holder.productPriceTxt.setText(product.getPrice() + "");

    /*If a product exists in shared preferences then set heart_red drawable
     * and set a tag*/
    if (checkFavoriteItem(product)) {
        holder.favoriteImg.setImageResource(R.drawable.heart_red);
        holder.favoriteImg.setTag("red");
    } else {
        holder.favoriteImg.setImageResource(R.drawable.heart_grey);
        holder.favoriteImg.setTag("grey");
    }

    return convertView;

}

/*Checks whether a particular product exists in SharedPreferences*/
public boolean checkFavoriteItem(Product checkProduct) {
    boolean check = false;
    List<Product> favorites = sharedPreference.getFavorites(context);
    if (favorites != null) {
        for (Product product : favorites) {
            if (product.equals(checkProduct)) {
                check = true;
                break;
            }
        }
    }
    return check;
}

@Override
public void add(Product product) {
    super.add(product);
    products.add(product);
    notifyDataSetChanged();
}

@Override
public void remove(Product product) {
    super.remove(product);
    products.remove(product);
    notifyDataSetChanged();
}   
}

单项 Activity

public class SingleItemView extends Activity
{
ProductListAdapter padaptr;
SharedPreference sharedPreference;

List<Product> products = null;

@Override
protected void onCreate(Bundle savedInstanceState)
{
    // TODO: Implement this method
    super.onCreate(savedInstanceState);
    setContentView(R.layout.singleitem);
    sharedPreference = new SharedPreference();
    padaptr = new ProductListAdapter(SingleItemView.this, products);





    Button btn = (Button) findViewById(R.id.singleitemButton1);
    btn.setOnClickListener(new OnClickListener(){
        @Override
        public void onClick(View v){
            products=new ArrayList<Product>();
            Bundle extras = getIntent().getExtras();

            String jsonObj = extras.getString("selected item");


            ObjectMapper mapper = new ObjectMapper();

            try
            {
                Product pro = mapper.readValue(jsonObj, Product.class);

                if (checkFavoriteItem(pro)) {

                    sharedPreference.removeFavorite(SingleItemView.this, pro);

                    Toast.makeText(SingleItemView.this,
                                   SingleItemView.this.getResources().getString(R.string.remove_favr),
                                   Toast.LENGTH_SHORT).show();
                                   padaptr.notifyDataSetChanged();
                } else {
                    sharedPreference.addFavorite(SingleItemView.this, pro);
                    Toast.makeText(SingleItemView.this,
                                   SingleItemView.this.getResources().getString(R.string.add_favr),
                                   Toast.LENGTH_SHORT).show();
                                   padaptr.notifyDataSetChanged();


                }
            }
            catch (IOException e)
            {};





        }



            private boolean checkFavoriteItem(Product checkProduct) {
                boolean check = false;
                List<Product> favorites = sharedPreference.getFavorites(getApplicationContext());
                if (favorites != null) {
                    for (Product product : favorites) {
                        if (product.equals(checkProduct)) {
                            check = true;
                            break;
                        }
                    }
                }
                return check;
            }
    });
    }


}

Answer 1

当您返回 fragment/Activity 时，您需要将更改通知您的适配器。

使用 startActivityForResult() 开始您的第二个 Activity :

Intent intent = new Intent(activity.getApplicationContext(), SingleItemView.class);
intent.putExtra("selected item", jsonInString);
startActivityForResult(intent, 1);

然后覆盖 onActivityResult() 方法来处理回调，并使用 notifyDataSetChanged() 通知您的适配器:

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (requestCode == 1) {
        productListAdapter.notifyDataSetChanged();
    }
}