在自定义适配器notifyDataSetChanged上获取NullPointerException

丹尼尔·卡多佐（Daniel Cardoso）

我有一个自定义适配器，我试图从它删除一个项目后，我打电话notifyDataSetChanged()，我收到了nullPointerExeption。

我想从数据库中删除数据，所以我将一个OnClickListener传递给适配器，以便以后可以获取所需的信息以知道要删除的内容。

这是我的代码：

用ListView片段：

        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：

公共类TransactionAdapter扩展了BaseAdapter {

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;
}

项目布局：

<?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！

丹尼尔·卡多佐（Daniel Cardoso）

因此，问题在于我正在以编程方式添加和标识，并且与其他标识冲突

在适配器上，我正在做：

    btnRemove = (Button) convertView.findViewById(R.id.btnRemove);
    btnRemove.setOnClickListener(onClickListener);
    btnRemove.setTag(entry);
    btnRemove.setId(position);

在删除教程setId并在xml中使用id之后，我在教程中使用的代码一切正常。

谢谢大家

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