android - 将可检查的列表视图放入片段

Question

我正在尝试在列表视图顶部弹出一个带有按钮的可检查列表视图片段。用户单击导航菜单中的项目后，主活动将填充我的按钮和列表视图片段。即使声明了元素，我也会收到“调用虚拟方法”错误。这是一些代码。

我的列表片段类：

public class ThingsManager extends Fragment {

ArrayList<String> selectedItems;
ListView checkable_list;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(layout.things_manager_fragment, container, false);
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    //create an ArrayList object to store selected items
    selectedItems = new ArrayList<String>();
    //create an instance of ListView
    checkable_list.findViewById(R.id.checkable_list);
    //set multiple selection mode
    checkable_list.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
    String[] things_factory = {"Sports", "Politics", "Food", "Television", "Movies", "Fashion",
            "Theoretical Physics"};
    //supply data itmes to ListView
    //ArrayAdapter<String> aa = new ArrayAdapter<String>(this, R.layout.row, R.id.things_check, things_factory);
    ArrayAdapter<String> aa = new ArrayAdapter<String>(getActivity(),
            android.R.layout.simple_list_item_1, things_factory);
    checkable_list.setAdapter(aa);
    //set OnItemClickListener
    checkable_list.setOnItemClickListener(new AdapterView.OnItemClickListener(){
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            // selected item
            String selectedItem = ((TextView) view).getText().toString();
            if(selectedItems.contains(selectedItem))
                selectedItems.remove(selectedItem); //remove deselected item from the list of selected items
            else
                selectedItems.add(selectedItem); //add selected item to the list of selected items
        }
    });
}

public ThingsManager() {
    // Required empty public constructor
}
}

列表片段布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ThingsManager">

<TextView
    android:id="@+id/things_manager_header"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Things Manager"
    android:textSize="25dp"/>

<!-- TODO: Update blank fragment layout -->

    <ListView
        android:id="@+id/checkable_list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>

我应该在 MainActivity 还是在控制列表视图FragmentClass ？

标签： androidandroid-studiolistviewandroid-fragments

Answer 1

将所有视图初始化和列表视图设置代码从方法onActivityCreated移至 onCreateView方法。

而你的这句话

//create an instance of ListView
checkable_list.findViewById(R.id.checkable_list);

是错的。你必须ListView从你膨胀的视图中找到onCreateView。

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                     Bundle savedInstanceState) {
    // Inflate the layout for this fragment
   View rootView =  inflater.inflate(layout.things_manager_fragment, container, false);
   init(rootView);
   return rootView;
}

public void init(View rootView){


   //create an ArrayList object to store selected items
   selectedItems = new ArrayList<String>();
   //create an instance of ListView
   checkable_list = rootView.findViewById(R.id.checkable_list);
   //set multiple selection mode
   checkable_list.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
   String[] things_factory = {"Sports", "Politics", "Food", "Television", "Movies", "Fashion",
        "Theoretical Physics"};
   //supply data itmes to ListView
   //ArrayAdapter<String> aa = new ArrayAdapter<String>(this, R.layout.row, R.id.things_check, things_factory);
   ArrayAdapter<String> aa = new ArrayAdapter<String>(getActivity(),
        android.R.layout.simple_list_item_1, things_factory);
   checkable_list.setAdapter(aa);
   //set OnItemClickListener
   checkable_list.setOnItemClickListener(new AdapterView.OnItemClickListener(){
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        // selected item
        String selectedItem = ((TextView) view).getText().toString();
        if(selectedItems.contains(selectedItem))
            selectedItems.remove(selectedItem); //remove deselected item from the list of selected items
        else
            selectedItems.add(selectedItem); //add selected item to the list of selected items
    }
   });

}