嘗試對空對象引用調用虛擬方法“”

Question

我收到以下錯誤

嘗試在空對象引用上調用虛擬方法“void android.widget.StackView.setAdapter(android.widget.Adapter)”

在這條線上

stackView.setAdapter(adapter);

完整的片段EventsFragment.java是

public class EventsFragment extends android.support.v4.app.Fragment {
    private StackView stackView;
    private  ArrayList<Stack_Items> list;
    TypedArray eventLogo ;
    String eventName[];

    @Nullable
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        eventLogo= getResources().obtainTypedArray(R.array.event_stack_icon);
        eventName = getResources().getStringArray(R.array.event_stack);
        stackView = (StackView) getActivity().findViewById(R.id.stackView1);
        list = new ArrayList<Stack_Items>();

        //Adding items to the list
        for (int i = 0; i < eventLogo.length(); i++) {
            list.add(new Stack_Items(eventName[i], eventLogo.getResourceId(i,-1)));
        }
        //Calling adapter and setting it over stackView
        Stack_Adapter adapter = new Stack_Adapter(getActivity().getApplicationContext(), list );
        stackView.setAdapter(adapter);
        adapter.notifyDataSetChanged();
        return inflater.inflate(R.layout.events_layout, null);
    }
}

Stack_Adapter.java

public class Stack_Adapter extends BaseAdapter {

    ArrayList<Stack_Items> arrayList;
    LayoutInflater inflater;
    ViewHolder holder = null;

    public Stack_Adapter(Context context, ArrayList<Stack_Items> arrayList) {
        this.arrayList = arrayList;
        this.inflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return arrayList.size();
    }

    @Override
    public Stack_Items getItem(int pos) {
        return arrayList.get(pos);
    }

    @Override
    public long getItemId(int pos) {
        return pos;
    }

    @Override
    public View getView(int pos, View view, ViewGroup parent) {
        if (view == null) {
            view = inflater.inflate(R.layout.stack_layout, parent, false);
            holder = new ViewHolder();

            holder.text = (TextView) view.findViewById(R.id.textView1);
            holder.image = (ImageView) view.findViewById(R.id.imageView1);
            view.setTag(holder);
        } else {
            holder = (ViewHolder) view.getTag();
        }

        holder.text.setText(arrayList.get(pos).getName());
        holder.image.setBackgroundResource(arrayList.get(pos).getImage());

        return view;
    }

    public class ViewHolder {
        TextView text;
        ImageView image;
    }

}

Stack_Items

public class Stack_Items {
    String name;
    Integer image;

    public Stack_Items(String name, Integer image) {
        this.name = name;
        this.image = image;
    }

    public String getName() {
        return name;

    }

    public int getImage() {

        return image;
    }

}

Answer 1

你在做：

stackView = (StackView) getActivity().findViewById(R.id.stackView1);

您的stackView為null 。 getActivity().findViewById返回null 。

你為什么使用getActivity() ？

stackView在哪里？ 您應該從正確的 xml 加載它。

正如@Tauqir 所提到的，您需要像這樣膨脹正確的 xml：

View view = inflater.inflate(R.layout.events_layout, null);
stackView = (StackView) view.findViewById(R.id.stackView1);
return view;

Answer 2

在onCreateView里面試試這個

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.events_layout, null);

        -------------some codes ------------

        stackView = (StackView) view.findViewById(R.id.stackView1);

        -------------some codes ------------
        return view;

    }

Answer 3

R.id.stackView1當您嘗試分配未找到stackView ，所以它是null

Answer 4

做這個

View rootView = inflater.inflate(R.layout.events, container, false);
stackView = (StackView) rootview.findViewById(R.id.stackView1);
.
.
.
return rootview

您首先需要膨脹布局並在它返回的視圖上調用 findViewById()，因此 getActivity().findViewById 應該是 rootView.findViewByID。

您的代碼還有一些其他問題。 像 getctivity().getApplicationContext 一樣，只需要 getActivity() 就可以了。

Answer 5

將容器和 false 更改為 null

做這個：

View rootView = inflater.inflate(R.layout.events, null);