未分配改装回收器视图适配器列表

Question

我被卡住了

如您所见，列表为空，但我希望在将其传递给适配器之前将其分配给API的响应。但是List作为null传递并抛出null异常。在适配器初始化之前，我在onCreate((方法中调用了API方法，但它不起作用。

我无法理解我在这里错过了什么。如何才能不分配列表。我尝试初始化新的ArrayList，它没有抛出任何错误，但这次RecyclerView是空的。

有什么帮助吗？

代码：

public class InventoryInfoActivity extends AppCompatActivity {

InventoryInfoRecyclerViewAdapter inventoryInfoRecyclerViewAdapter;
RecyclerView recyclerView;
ProductService productService;
List<Product> productList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_inventory_info);
productService = new ProductService(this);
// CALL METHOD
this.getProductList();
recyclerView  = findViewById(R.id.recycler_inventory);
recyclerView.setLayoutManager(new LinearLayoutManager(InventoryInfoActivity.this));
inventoryInfoRecyclerViewAdapter = new InventoryInfoRecyclerViewAdapter(productList,this);
recyclerView.setAdapter(inventoryInfoRecyclerViewAdapter);
}
// API REQUEST
private void getProductList() {
productService.getProducts().enqueue(new Callback<List<Product>>() {
@Override
public void onResponse(Call<List<Product>> call, Response<List<Product>> response) {
if (response.isSuccessful()) {
Log.i("REQUEST","OK");
// ASSIGN
productList = response.body();
}else {
Log.i("REQUEST","BAD");
productList = new ArrayList<>();
}
}
@Override
public void onFailure(Call<List<Product>> call, Throwable t) {
Log.i("REQUEST","FAILED");
productList = new ArrayList<>();
}
});
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.search_action,menu);
MenuItem menuItem = menu.findItem(R.id.action_search);
SearchView searchView = (SearchView) menuItem.getActionView();
searchView.setQueryHint("Ara");
searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
@Override
public boolean onQueryTextSubmit(String query) {
return false;
}
@Override
public boolean onQueryTextChange(String newText) {
filter(newText);
return false;
}
});

return super.onCreateOptionsMenu(menu);
}
private void filter(String text) {
ArrayList<Product> filteredlist = new ArrayList<>();
for (Product item : productList) {
if (item.getProductName().toLowerCase().contains(text.toLowerCase())) {
filteredlist.add(item);
}
}
if (filteredlist.isEmpty()) {
Toast.makeText(this, "Böyle bir ürün yok", Toast.LENGTH_SHORT).show();
} else {
inventoryInfoRecyclerViewAdapter.filterList(filteredlist);
}
}
}

LogCat:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.tempter.stoktakip, PID: 32165
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference

Answer 1

这里的问题是，在收到响应后，您应该通知适配器您有一个新的List。RecyclerView中有许多很酷的方法，称为notifiyDataSetChanged。

你所做的并不全是错的。让我解释一下你可以在你的代码中做什么：

1. 您定义的变量是一个没有任何值的列表，因此为null

private List<Product> items = new ArrayList<Product>();

或者你应该修复适配器中的getItems方法，如下所示：

public int getItems() {
return items == null || items.isEmpty() ? 0 : items.size();
}

2. 收到响应后，请将新列表传递给适配器。首先，您需要在适配器中创建一个方法来传递这些数据，如下所示

//  in your adapter
public void setData(List<String> newItems) {
adapterItems.clear();
adapterItems.addAll(newItems);
notifyDataSetChange();
}

然后在你成功调用api之后，你应该像下面这样做：

private void getProductList() {
productService.getProducts().enqueue(new Callback<List<Product>>() {
@Override
public void onResponse(Call<List<Product>> call, Response<List<Product>> response) {
if (response.isSuccessful()) {
Log.i("REQUEST", "OK");
// ASSIGN
productList = response.body();

//!! This is here important
inventoryInfoRecyclerViewAdapter.setData(productList);
//!! This is here important 
} else {
Log.i("REQUEST", "BAD");
productList = new ArrayList<>();
}
}
@Override
public void onFailure(Call<List<Product>> call, Throwable t) {
Log.i("REQUEST", "FAILED");
productList = new ArrayList<>();
}
});
}

现在就这样了。你现在应该用新列表更新你的recyclerView。

Answer 2

首先，在onCreate的末尾调用getProductList。

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState); 
List<Product> productlist = new ArrayList<Product>();
setContentView(R.layout.activity_inventory_info);
productService = new ProductService(this);
recyclerView  = findViewById(R.id.recycler_inventory);
recyclerView.setLayoutManager(new LinearLayoutManager(InventoryInfoActivity.this));
inventoryInfoRecyclerViewAdapter = new InventoryInfoRecyclerViewAdapter(productList,this);
recyclerView.setAdapter(inventoryInfoRecyclerViewAdapter);
this.getProductList();
}

那么我认为getProductList应该返回一个产品列表或另一个类的列表。

private ArrayList<Product> getProductList() {
productService.getProducts().enqueue(new Callback<List<Product>>() {
@Override
public void onResponse(Call<List<Product>> call, Response<List<Product>> response) {
if (response.isSuccessful()) {
Log.i("REQUEST","OK");
// ASSIGN
productList = response.body();
}else {
Log.i("REQUEST","BAD");
productList = new ArrayList<>();
}
}
@Override
public void onFailure(Call<List<Product>> call, Throwable t) {
Log.i("REQUEST","FAILED");
productList = new ArrayList<>();
}
});
}
return productList;