Question

看了很多其他帖子并尝试了几种变化但到目前为止没有运气......

使用以下自定义列表适配器获取NPE：

public ListView tripList;
....
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    ....

        // build a listView adapter
        Log.i(LOGTAG,"About to create listView...");
        tripList = (ListView) findViewById(android.R.id.list);
        Log.i(LOGTAG,"ListView created...");

        Log.i(LOGTAG,"About to create adapter...");
        tripAdapter = new tripListAdapter(this, tripCur);
        setListAdapter(tripAdapter);

    }

    setContentView(R.layout.activity_trip_display);

...和适配器有这个：

// custom list adaptor class
private class tripListAdapter extends CursorAdapter {

    //private final Cursor dataC;
    private final LayoutInflater vi;

    public tripListAdapter(Context con, Cursor c) {
        // super constructor thingy
        super(con, c);
        //dataC = c;
        vi = LayoutInflater.from(con);

    }

@Override
    public View getView (int position, View tripView, ViewGroup parent){

        Log.i(LOGTAG,"In getView...");
        // Create a message handling object as an anonymous class.
        //mTripClickHandler = new OnItemClickListener() {

// NPE ERROR ON THIS NEXT LINE (line 228):
        tripList.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
                // Do something in response to the click
                // Enable other buttons
                togBtns(true);

logcat的：

06-13 09:47:49.195: I/WIBBLE(864): ListView created...
06-13 09:47:49.195: I/WIBBLE(864): About to create adapter...
06-13 09:47:49.285: I/WIBBLE(864): OnResume with this many rows returned by cursor: 3
06-13 09:47:49.285: I/WIBBLE(864): In the loop, so cursor is not null....
06-13 09:47:49.375: I/WIBBLE(864): In getView...
06-13 09:47:49.387: D/AndroidRuntime(864): Shutting down VM
06-13 09:47:49.387: W/dalvikvm(864): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
06-13 09:47:49.505: E/AndroidRuntime(864): FATAL EXCEPTION: main
06-13 09:47:49.505: E/AndroidRuntime(864): java.lang.NullPointerException
06-13 09:47:49.505: E/AndroidRuntime(864):  at  com.example.myfirstapp.DisplayTripsActivity$tripListAdapter.getView(DisplayTripsActivity.java:228)
06-13 09:47:49.505: E/AndroidRuntime(864):  at android.widget.AbsListView.obtainView(AbsListView.java:2177)
06-13 09:47:49.505: E/AndroidRuntime(864):  at android.widget.ListView.measureHeightOfChildren(ListView.java:1247)
06-13 09:47:49.505: E/AndroidRuntime(864):  at android.widget.ListView.onMeasure(ListView.java:1159)
06-13 09:47:49.505: E/AndroidRuntime(864):  at android.view.View.measure(View.java:15848)
06-13 09:47:49.505: E/AndroidRuntime(864):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008)

感谢任何建议。

编辑：如果我更换：

//tripList = (ListView) findViewById(android.R.id.list);

使用：

tripList = getListView();

...我继续前进（参见WIBBLE消息）但获得另一个NPE，虽然似乎在某些系统例程中：

06-13 10:26:49.825: I/WIBBLE(934): About to create listView...
06-13 10:26:49.865: I/WIBBLE(934): ListView created...
06-13 10:26:49.865: I/WIBBLE(934): About to create adapter...
06-13 10:26:49.945: I/WIBBLE(934): OnResume with this many rows returned by cursor: 3
06-13 10:26:49.945: I/WIBBLE(934): In the loop, so cursor is not null....
06-13 10:26:50.035: I/WIBBLE(934): In getView...
06-13 10:26:50.035: I/WIBBLE(934): Leaving getView...
06-13 10:26:50.035: D/AndroidRuntime(934): Shutting down VM
06-13 10:26:50.035: W/dalvikvm(934): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
06-13 10:26:50.185: E/AndroidRuntime(934): FATAL EXCEPTION: main
06-13 10:26:50.185: E/AndroidRuntime(934): java.lang.NullPointerException
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.widget.AbsListView.obtainView(AbsListView.java:2179)
06-13 10:26:50.185: E/AndroidRuntime(934):  at  android.widget.ListView.measureHeightOfChildren(ListView.java:1247)
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.widget.ListView.onMeasure(ListView.java:1159)
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.view.View.measure(View.java:15848)
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008)
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1052)
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.widget.LinearLayout.onMeasure(LinearLayout.java:590)
06-13 10:26:50.185: E/AndroidRuntime(934):  at android.view.View.measure(View.java:15848)

......以及许多其他行，没有引用我的代码。

Answer 1

您不应该从onItemClickListener设置Adapter。 Adapter仅关注创建单个列表项视图。在视图充气后，从onItemClickListener（或Activity）设置Fragment。

看起来您当前没有设置您的活动视图，这就是tripList ListView为NULL的原因。使用setContentView(R.layout.your_layout)将视图设置为xml布局。

您可能希望发布大部分代码。这是活动还是碎片？您是否扩展了基本活动/片段，或其他类似ListActivity / ListFragment。我想知道因为你正在访问android的R文件而不是你自己的（android.R.id.list vs R.id.list）

<强>更新

好的，我已经回答了我自己的问题。您正在使用ListActivity（或ListFragment），这就是您使用android的R文件的原因。我会将其更改为getListView()而不是findViewById。我仍然会移动setOnItemClickListener并发布新的NPE例外，因为这是执行此操作的正确方法。

Answer 2

将tripView变量分配给ListView时，使用：

tripList = (ListView) findViewById(android.R.id.list);

尝试将此行更改为：

tripList = (ListView) findViewById(R.id.list);

不是在android.R中搜索正确的项目（它可能不会退出），而是在构建项目时生成的R文件中查找ListView项目。

确保在运行之前重建项目。

使用自定义适配器和Listview OnClick

2 个答案: