java - 在自定义适配器notifyDataSetChanged上获取NullPointerException

Question

已关闭。此问题需要 debugging details 。目前不接受答案。

---

编辑问题以包含 desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem 。这将有助于其他人回答问题。

已关闭 8 年前。

Improve this question

我有一个自定义适配器，在调用notifyDataSetChanged()后我试图从中删除一个项目。我得到一个nullPointerExeption .

我想从数据库中删除数据，因此我将 OnClickListener 传递给适配器，以便稍后获取了解要删除的内容所需的信息。

这是我的代码:

使用 ListView 进行 fragment

        adapter = new TransactionAdapter(getActivity(), values,currency);
        adapter.setButtonOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                RelativeLayout l = (RelativeLayout) v.getParent();
                String id_string = ((TextView) l.findViewById(R.id.transaction_id)).getText() +"";
                int id = Integer.parseInt(id_string);
                //Remove from DB
                if(adapter.remove(id)){
                    adapter.notifyDataSetChanged();
                }
                Toast.makeText(getActivity(), "deleted entry - "+ id, Toast.LENGTH_SHORT).show();
            }
        });
        // Assign adapter to ListView
        listView.setAdapter(adapter);

适配器:

公共(public)类 TransactionAdapter 扩展 BaseAdapter { 私有(private)Context上下文；

private OnClickListener onClickListener;
private List<Transaction> listTransaction;

private String currency;

public TransactionAdapter(Context context, List<Transaction> listTransaction, String currency) {
    this.context = context;
    this.listTransaction = listTransaction;
    this.currency = currency;
}

public void setButtonOnClickListener(OnClickListener c){
    onClickListener = c;
}

public View getView(int position, View convertView, ViewGroup viewGroup) {
    if (convertView == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.transaction_item_layout, null);
    }
    convertView.setClickable(false);
    Transaction entry = listTransaction.get(position);
    TextView tvDescription = (TextView) convertView.findViewById(R.id.description);
    String description = entry.getDescription();
    if(description == null){
        description = "Description Filler";
    }
    tvDescription.setText(description);

    TextView tvAmount = (TextView) convertView.findViewById(R.id.amount);

    Boolean expense = entry.getExpense();
    if(expense) {
        tvAmount.setText("- " + entry.getAmount().toString() + currency);
        tvAmount.setTextColor(context.getResources().getColor(R.color.buttons_color_delete));
    }else{
        tvAmount.setText("+ " + entry.getAmount().toString() + currency);
        tvAmount.setTextColor(context.getResources().getColor(R.color.second_elements_color));
    }

    TextView tvID = (TextView) convertView.findViewById(R.id.transaction_id);
    tvID.setText(entry.getId()+"");

    // Set the onClick Listener on this button
    Button btnRemove = (Button) convertView.findViewById(R.id.btnRemove);
    btnRemove.setOnClickListener(onClickListener);
    btnRemove.setTag(entry);
    btnRemove.setId(position);


    return convertView;
}

public boolean remove(int id){
    for (int i = 0; i < listTransaction.size(); i++) {
        Transaction t = listTransaction.get(i);
        if(id == t.getId()){
            listTransaction.remove(i);
            return true;
        }
    }
    return false;
}

Item_layout:

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<RelativeLayout
    android:id="@+id/transaction_item"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:paddingTop="10dp"
    android:paddingBottom="10dp"
    android:layout_marginTop="1dp"
    android:layout_marginLeft="1dp"
    android:layout_marginRight="1dp"
    android:orientation="horizontal"
    android:background="@drawable/edittext_create_budget">
    <TextView
        android:id="@+id/description"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@color/create_budget_edit_text"
        android:layout_marginLeft="15dp"
        android:layout_marginStart="15dp"
        android:gravity="center_vertical"
        android:text="@string/start_date" />

    <TextView
        android:id="@+id/transaction_id"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="id"
        android:visibility="gone"/>

    <TextView
        android:id="@+id/amount"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="15dp"
        android:layout_marginStart="15dp"
        android:layout_toLeftOf="@+id/btnRemove"
        android:layout_toStartOf="@+id/btnRemove"
        android:gravity="center_vertical"
        android:textColor="@color/create_budget_edit_text"
        android:textSize="20sp"
        android:text="23.05€" />

    <Button
        android:id="@+id/btnRemove"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_marginLeft="15dp"
        android:layout_marginStart="15dp"
        android:layout_marginRight="15dp"
        android:layout_marginEnd="15dp"
        android:background="@drawable/round_button"
        android:text="R" />

</RelativeLayout>

这是StackTrace:

java.lang.NullPointerException: Attempt to invoke virtual method 'void     android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at TransactionAdapter.getView(TransactionAdapter.java:75)
        at android.widget.AbsListView.obtainView(AbsListView.java:2344)
        at android.widget.ListView.makeAndAddView(ListView.java:1864)
        at android.widget.ListView.fillSpecific(ListView.java:1344)
        at android.widget.ListView.layoutChildren(ListView.java:1651)
        at android.widget.AbsListView.onLayout(AbsListView.java:2148)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.support.v4.widget.DrawerLayout.onLayout(DrawerLayout.java:887)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at com.android.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:494)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2072)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1829)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:550)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

谢谢!

Answer 1

您使用了错误类型的 OnClickListener!

这是我的代码:

receiverList = dbTools.getAllReceivers();
dbTools.close();
listView = getListView();
if(receiverList.size() != 0) {
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int index, long id) {
        TextView textView = (TextView) view.findViewById(R.id.receiverId);

        setReceiverSelection(Integer.valueOf(textView.getText().toString()));
            ((SimpleAdapter) getListAdapter()).notifyDataSetChanged();
        }
    });
    SimpleAdapter adapter = getNewAdapter();
    setListAdapter(adapter);
}

您需要使用AdapterView.OnItemClickListener()。在其 onItemClick() 方法中，您将获得被单击的行的 view 和 index。

希望这有帮助。祝你好运:)

编辑:

如果您希望在该行中的按钮上有一个监听器，这是最简单的方法。

在所添加行的 XML 中，将 android:onClick="methodName" 添加到按钮的 XML 中。

然后在您拥有 ListView 的 Activity 中，添加底部，添加一个名为 methodName 的方法，该方法将 View 作为参数。它会看起来像这样。

public void methodName(View view) {

}

现在，我们要找出哪一行的按钮被按下。

我是这样做的:

public void methodName(View view) {

    LinearLayout vwParentRow = (LinearLayout)view.getParent();
    TextView recId = (TextView) vwParentRow.findViewById(R.id.receiverId);

    System.out.println(recId.getText().toString() + " had its button pressed!");

}

如果您的按钮“埋”得更深(例如，如果您的 LinearLayout 内部有一个 LinearLayout 并且按钮位于其中，只需获取该按钮的父级即可家长:

LinearLayout parentOfParent = (LinearLayout) vwParentRow.getParent();

编辑2:据我所知，您还可以以编程方式添加监听器，并让它执行与我在 methodName 中向您展示的相同的 onClick 操作。我展示的方式绝对有效 - 我在我的应用程序中使用了它。