Question

我正在通过John Horton的 Android初学者编程，目前我正在尝试创建一个笔记记录应用。霍顿刚刚介绍了ListViews。但是，我在使用adapter class：

时遇到问题

public class NoteAdapter extends BaseAdapter {

    List<Note> mNoteList = new ArrayList<Note>(); 

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

    @Override
    public Note getItem(int whichItem){
        return mNoteList.get(whichItem);
    }

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

    @Override
    public View getView(int whichItem, View view, ViewGroup viewGroup){

        // check if view has been inflated already
        if (view == null){
            LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE); // ERROR HERE

            view = inflater.inflate(R.layout.listitem, viewGroup, false);

        }

        return view;
    }

}

问题在于getView方法，我尝试inflate layout：Android Studio throws an error: 'Cannot resolve getSystemService(java.lang.String)'.

作为一个完整的新人，只是通过这本书，我不知道从这里去哪里或尝试解决它 - 可以有人帮忙吗？

Answer 1

获得LayoutInflater的最佳方法是致电getLayoutInflater()上的Activity。这样，活动的主题就被考虑在内了。如果NoteAdapter内定义了Activity，请致电getLayoutInflater()。如果NoteAdapter在其自己的单独Java类文件中定义，则通过构造函数传入LayoutInflater。

要更直接地解决您的问题，任何View（例如ListView）都可以致电getContext()获取Context。这就是定义getSystemService()的地方。因此，将getSystemService()替换为viewGroup.getContext().getSystemService()会有效。

Answer 2

使用 view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.listitem, viewGroup,false);

Answer 3

您应该将上下文传递给适配器，然后替换此行：

 LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

我希望这会有所帮助。

Answer 4

为适配器创建一个类变量和一个构造函数：

Context context;
public NoteAdapter(Context context){
this.context = context;
}

然后按以下方式初始化layoutinflater：

LayoutInflater inflater = LayoutInflater.from(context);

Answer 5

在我看来，如果你正在学习，那么学习RecyclerView。 bcz它比ListView更好。我并不是说ListView已被删除。但是有很多内部事物，其中RecyclerView更好。

以下是适配器

的示例

public class NoteAdapter extends BaseAdapter {

    List<Note> mNoteList = new ArrayList<Note>();

    Context context;

    public NoteAdapter(Context context){
        this.context = context;
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 

    }

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

    @Override
    public Note getItem(int whichItem){
        return mNoteList.get(whichItem);
    }

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

    @Override
    public View getView(int whichItem, View view, ViewGroup viewGroup){

        // check if view has been inflated already 
        if (view == null){

            view = inflater.inflate(R.layout.listitem, viewGroup, false);

        }

        return view;
    }

}

在MainActivity.java内部

NoteAdapter noteA = new NoteAdapter(MainActivity.this);

OR

NoteAdapter noteA = new NoteAdapter(getContext());

OR

NoteAdapter noteA = new NoteAdapter(getActivity);

//如果在Fragment中

OR

NoteAdapter noteA = new NoteAdapter(getApplicationContext);

//将起作用但不需要使用它。 bcz这是整个应用的背景。对于适配器，您不需要整个应用程序的上下文。

Answer 6

尝试

public class NoteAdapter extends BaseAdapter {

    Context mContext = null;

    public NoteAdapter(Context context){
       mContext = context;
    }


    @Override
    public View getView(int whichItem, View view, ViewGroup viewGroup){

        // check if view has been inflated already
        if (view == null){
            LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE); // ERROR HERE

            view = inflater.inflate(R.layout.listitem, viewGroup, false);

        }

        return view;
    }

}

Answer 7

首先制作Adapter的构造函数：如下：

Context context;
public NoteAdapter(Context context)
{
  this.context = context
}

现在使用此上下文：

LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

Answer 8

mContext是您传递给自定义适配器的上下文

  public boolean CheckInternet() {
        ConnectivityManager connectivityManager = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
        if (connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE).getState() == NetworkInfo.State.CONNECTED ||
                connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI).getState() == NetworkInfo.State.CONNECTED) {
            //we are connected to a network
            return true;
        }
        return false;
    }//end of check internet

无法解析ListView适配器

8 个答案: