Question

因此，当我尝试设置自定义适配器时，我经常会得到一个nullpointer。我无法弄清楚什么是错的。得到一个错误说这主要是代码所以这个文本很容易填补空间。

我设置适配器的代码：

AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setTitle("Select a match");

//insert array to constructor
LayoutInflater inflater = getLayoutInflater(savedInstanceState);
View dialogLayout = inflater.inflate(R.layout.dialoglist, null);
ListAdapter testAdapter = new matchAdapter(getActivity().getApplicationContext(), userInfos);
ListView listView = (ListView) getView().findViewById(R.id.dialogListView);
listView.setAdapter(testAdapter);
builder.setView(dialogLayout);

AlertDialog alert = builder.create();
alert.show();

自定义适配器：

class matchAdapter extends ArrayAdapter<userInfo> {

    public matchAdapter(Context context, ArrayList<userInfo> test) {
        super(context, R.layout.match_result, test);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = LayoutInflater.from(getContext());

        View customRow = inflater.inflate(R.layout.match_result, parent, false);
        userInfo singleItemTest = getItem(position);

        /*
        TODO: get references to layout elements
         */

        TextView username = (TextView) customRow.findViewById(R.id.matchUsername);
        TextView sex = (TextView) customRow.findViewById(R.id.matchSex);
        TextView age = (TextView) customRow.findViewById(R.id.matchAge);
        Button sendRequest = (Button) customRow.findViewById(R.id.matchSendRequest);

        username.setText(singleItemTest.getUserName());

        return customRow;
    }
}

dialoglist.xml：

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

    <ListView xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/dialogListView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </ListView>

</RelativeLayout>

来自logcat的

stacktrace：

FATAL EXCEPTION: main

Process: com.example.j.airportmeet, PID: 20123
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
    at com.example.j.airportmeet.flightFragment$11.onClick(flightFragment.java:297)
    at android.view.View.performClick(View.java:5201)
    at android.view.View$PerformClick.run(View.java:21163)
    at android.os.Handler.handleCallback(Handler.java:746)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5443)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)

Answer 1

问题在于：

ListView listView = (ListView) getView().findViewById(R.id.dialogListView);

我不确切知道getView()到底是什么，但我知道你的ListView并不存在。您已在此处创建了视图

View dialogLayout = inflater.inflate(R.layout.dialoglist, null);

并应在此视图中搜索ListView。

ListView listView = (ListView) dialogLayout.findViewById(R.id.dialogListView);

ListAdapter setAdapter返回null

1 个答案: