java - 滚动时出现惰性列表适配器问题

Question

public View getView(int position, View convertView, ViewGroup parent) {         
    ViewHolder viewHolder = null;
    View vi= convertView;

    if(convertView==null){
        viewHolder = new ViewHolder();
        vi = inflater.inflate(R.layout.list_row, null);
        viewHolder.content = (TextView)vi.findViewById(R.id.f_content);
        viewHolder.cat_id  = (TextView)vi.findViewById(R.id.c_id);
        viewHolder.fact_id = (TextView)vi.findViewById(R.id.f_id);
        vi.setTag(viewHolder); 
    }else{
        viewHolder = (ViewHolder) convertView.getTag();
    }   

    HashMap<String, String> fact = new HashMap<String, String>();
    fact = data.get(position);

    // Setting all values in listview
    viewHolder.fact_id.setText(fact.get("_id"));
    viewHolder.cat_id.setText(fact.get("cat_id"));
    viewHolder.content.setText(fact.get("fact_content"));

    return vi;
}

我创建了一个 LazyAdapter，它扩展了 BaseAdaper 以与 ListView 一起使用。

此适配器填充 ListView 中的数据。当我单击前 4 个可见列表项时，它会打印该项目的值。问题是当我向下滚动 ListView 并单击第 5 项时。应用程序崩溃并提示空指针异常。日志跟踪在这里供引用。

05-13 23:10:43.943: E/AndroidRuntime(3360): FATAL EXCEPTION: main 05-13 23:10:43.943: E/AndroidRuntime(3360): java.lang.NullPointerException 05-13 23:10:43.943: E/AndroidRuntime(3360): at com.example.facts.MainActivity$3.onItemClick(MainActivity.java:100) 05-13 23:10:43.943: E/AndroidRuntime(3360): at android.widget.AdapterView.performItemClick(AdapterView.java:284) 05-13 23:10:43.943: E/AndroidRuntime(3360): at android.widget.ListView.performItemClick(ListView.java:3569) 05-13 23:10:43.943: E/AndroidRuntime(3360): at android.widget.AbsListView$PerformClick.run(AbsListView.java:1831) 05-13 23:10:43.943: E/AndroidRuntime(3360): at android.os.Handler.handleCallback(Handler.java:587) 05-13 23:10:43.943: E/AndroidRuntime(3360): at android.os.Handler.dispatchMessage(Handler.java:92) 05-13 23:10:43.943: E/AndroidRuntime(3360): at android.os.Looper.loop(Looper.java:150) 05-13 23:10:43.943: E/AndroidRuntime(3360): at android.app.ActivityThread.main(ActivityThread.java:4389) 05-13 23:10:43.943: E/AndroidRuntime(3360): at java.lang.reflect.Method.invokeNative(Native Method) 05-13 23:10:43.943: E/AndroidRuntime(3360): at java.lang.reflect.Method.invoke(Method.java:507) 05-13 23:10:43.943: E/AndroidRuntime(3360): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849) 05-13 23:10:43.943: E/AndroidRuntime(3360): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607) 05-13 23:10:43.943: E/AndroidRuntime(3360): at dalvik.system.NativeStart.main(Native Method)

Onclick 方法如下:

// Click event for single list row
list.setOnItemClickListener(new OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view,
        int position, long id) {

    RelativeLayout node = (RelativeLayout)parent.getChildAt(position);
    TextView fact = (TextView) node.findViewById(R.id.c_id);
    Log.d("ListItem Clicked", "id: " + id + " position: "
        + position + " artist " + fact.getText());
}
});

Answer 1

我的建议是重新访问您的 onItemClickListener 实现。

您根本不需要访问父级来完成您想要做的事情。试试这个。

list.setOnItemClickListener(new OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view,
        int position, long id) {

        TextView fact = (TextView) view.findViewById(R.id.c_id);
        Log.d("ListItem Clicked", "id: " + id + " position: "
        + position + " artist " + fact.getText());
    }
});

该方法中提供的 View 参数实际上是正在单击的 View 。

view; The view within the AdapterView that was clicked (this will be a view provided by the adapter)

请引用AdapterView.OnItemClickListener了解更多详情。

父级可以帮助您识别正在执行操作的 AdapterView。例如，假设您有两个 ListAdapter 但只想使用一个监听器，那么它将帮助您指定哪个监听器。