我已经尝试让它工作大约 10 个小时但没有成功，我已经查看了堆栈溢出。我正在尝试显示一个简单的对话框并处理一些简单的输入。
它有一个TextView作为标题，EditText作为输入字段，以及两个按钮继续操作或取消。
出于某种原因，无论我做什么，我似乎都无法引用我的 shopping_dialogue xml 布局中的任何 View 。它给了我这个错误:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
我尝试向按钮添加一个 onClick 事件以查看是否有效，当我尝试在 onClick 方法中引用该按钮时，它给了我同样的错误。我正在使用一个 fragment 来执行此操作。
shopping_dialog.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<TextView
android:id="@+id/shoppingDialogTextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="Edit Shopping List Name" />
<EditText
android:id="@+id/shoppingDialogEditText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="30"
android:inputType="textPersonName"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">
<Button
android:id="@+id/shoppingDialogOk"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button" />
<Button
android:id="@+id/shoppingDialogCancel"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:onClick="k"
android:text="Button" />
</LinearLayout>
shopping_list_row.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
card_view:cardCornerRadius="4dp"
android:id="@+id/shoppingList_card_view"
android:layout_margin="10dp"
android:layout_height="200dp">
<LinearLayout
android:id="@+id/shoppingListParent"
android:layout_gravity="center"
android:layout_width="match_parent"
android:orientation="vertical"
android:gravity="center"
android:layout_height="match_parent">
<TextView
android:id="@+id/shoppingName"
android:layout_width="wrap_content"
android:gravity="center"
android:textSize="25sp"
android:textColor="#FFF"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/shoppingDate"
android:layout_width="wrap_content"
android:gravity="center"
android:textSize="25sp"
android:textColor="#FFF"
android:layout_height="wrap_content" />
</LinearLayout>
</androidx.cardview.widget.CardView>
fragment_shopping_list.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/shoppingList_recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
ShopingAdapter.java
public class ShoppingAdapter extends RecyclerView.Adapter<ShoppingAdapter.ShoppingViewHolder> {
private List<ShoppingData> shoppingList;
private Context context;
public ShoppingAdapter(List<ShoppingData> shoppingList, Context context){
this.shoppingList = shoppingList;
this.context = context;
}
@NonNull
@Override
public ShoppingViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i){
View itemView = LayoutInflater.from(viewGroup.getContext())
.inflate(R.layout.shopping_list_row, viewGroup, false);
return new ShoppingViewHolder(itemView);
}
@Override
public void onBindViewHolder(ShoppingViewHolder viewHolder, int i){
ShoppingData data = shoppingList.get(i);
Random k = new Random();
int color = Color.argb(255,k.nextInt(255),k.nextInt(255),k.nextInt(255));
viewHolder.parent.setBackgroundColor(color);
viewHolder.shoppingName.setText(data.getName());
viewHolder.shoppingDate.setText(data.getDate());
viewHolder.shoppingName.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder builder1 = new AlertDialog.Builder(v.getContext());
builder1.setCancelable(true);
builder1.setView(R.layout.shopping_dialog);
AlertDialog alert = builder1.create();
/*
EditText text = v.findViewById(R.id.shoppingDialogEditText);
text.setText("Some Text");
This causes a null object reference
*/
alert.show();
}
});
}
@Override
public int getItemCount(){return shoppingList.size();}
public class ShoppingViewHolder extends RecyclerView.ViewHolder{
private TextView shoppingName, shoppingDate;
private LinearLayout parent;
public ShoppingViewHolder(View itemView){
super(itemView);
parent = itemView.findViewById(R.id.shoppingListParent);
shoppingName = itemView.findViewById(R.id.shoppingName);
shoppingDate = itemView.findViewById(R.id.shoppingDate);
}
}
}
ShoppingFragment.java
public class ShoppingFragment extends Fragment {
private RecyclerView recyclerView;
private ShoppingAdapter shoppingAdapter;
private List<ShoppingData> shoppingList = new ArrayList<>();
@NonNull
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
@Nullable Bundle savedInstanceState){
shoppingList.add(new ShoppingData("k","12/12/12"));
shoppingList.add(new ShoppingData("k","12/12/12"));
shoppingList.add(new ShoppingData("k","12/12/12"));
shoppingList.add(new ShoppingData("k","12/12/12"));
shoppingList.add(new ShoppingData("k","12/12/12"));
shoppingList.add(new ShoppingData("k","12/12/12"));
View rootView = inflater.inflate(R.layout.fragment_shopping_list, container, false);
recyclerView = rootView.findViewById(R.id.shoppingList_recycler_view);
shoppingAdapter = new ShoppingAdapter(shoppingList, getActivity());
RecyclerView.LayoutManager manager = new GridLayoutManager(getActivity(), 2);
recyclerView.setLayoutManager(manager);
recyclerView.setAdapter(shoppingAdapter);
return rootView;
}
public void k(View view){ //the click listern that causes a null object reference when referencing the button
Button button = view.findViewById(R.id.shoppingDialogOk);
button.setText("k");
}
}
ShoppingData.java
package com.uhcl.recipe5nd.helperClasses;
public class ShoppingData {
private String name;
private String date;
public ShoppingData(String name, String date){
this.name = name;
this.date = date;
}
public String getDate(){
return this.date;
}
public String getName(){
return this.name;
}
}
一切正常，直到我尝试引用 shopping_dialog.xml 中的任何内容。
如果您查看我的购物适配器类，我想要做的就是向 onBindViewHolder 方法内的“shoppigName” TextView 添加一个 onClick 监听器。这是有效的，但是当我尝试引用 shoppingDialogEditText 时，它会导致应用程序崩溃并给我该错误。
就像我提到的，我还尝试将点击事件方法 k 添加到 shopping_dialog.xml 内的按钮，并在我的 fragment 类中实现它，看看是否可行，但仍然会导致同样的错误。
最佳答案
viewHolder.shoppingName.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
View dailogView = LayoutInflater.from(mContext).inflate(R.layout.shopping_dialog, null);
AlertDialog.Builder builder1 = new AlertDialog.Builder(v.getContext());
builder1.setCancelable(true);
builder1.setView(dailogView);
AlertDialog alert = builder1.create();
EditText text = dailogView.findViewById(R.id.shoppingDialogEditText);
text.setText("Some Text");
alert.show();
}
});
您用来查找edittext的 View 不是该对话框的 View ，因此它抛出空指针。
关于java - 在适配器内打开一个对话框返回空值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/58795966/