java - 错误 : incompatible types: HomeFragment cannot be converted to Context

Question

我的 Adapter 出错，这是我的代码，错误指向这段代码，它在 HomeFragment.java 上，它说:

error: incompatible types: HomeFragment cannot be converted to Context

adapter = new Adapter(models,this);

这是我的HomeFragment.java

public class HomeFragment extends Fragment {

    //cardview
    ViewPager viewPager;
    Adapter adapter;
    List<Model> models;
    Integer[]colors = null;
    ArgbEvaluator argbEvaluator = new ArgbEvaluator();


    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_home,container,false);

        //cardview
        models = new ArrayList<>();
        models.add(new Model(R.drawable.brochure,"Brochure","Lorem ipsum dolor sit amet"));
        models.add(new Model(R.drawable.sticker,"Sticker","Lorem ipsum dolor sit amet"));
       models.add(new Model(R.drawable.poster,"Poster","Lorem ipsum dolor sit amet"));
       models.add(new Model(R.drawable.namecard,"Name Card","Lorem ipsum dolor sit amet"));

        adapter = new Adapter(models,this);

        viewPager = getView().findViewById(R.id.viewPager);
        viewPager.setAdapter(adapter);
        viewPager.setPadding(130,0,130,0);
    }
}

然后这是我的Adapter.java

public class Adapter extends PagerAdapter {

    private List<Model> models;
    private LayoutInflater layoutInflater;
    private Context context;

    public Adapter(List<Model> models, Context context) {
        this.models = models;
        this.context = context;
    }

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

    @Override
    public boolean isViewFromObject(View view, @NonNull Object object) {
        return view.equals(object);
    }

    @NonNull
    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        layoutInflater = LayoutInflater.from(context);
        View view = layoutInflater.inflate(R.layout.item,container,false);

        ImageView imageView;
        TextView title,desc;

        imageView = view.findViewById(R.id.image);
        title = view.findViewById(R.id.title);
        desc = view.findViewById(R.id.desc);

        imageView.setImageResource(models.get(position).getImage());
        title.setText(models.get(position).getTitle());
        desc.setText(models.get(position).getDesc());

        container.addView(view,0);
        return view;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, @NonNull Object object) {
        container.removeView((View)object);
    }
}

Answer 1

改变这个:

adapter = new Adapter(models,this);

为此:

adapter = new Adapter(models, (Context) getActivity());

您必须传递 Context。 Activity 可以转换为 Context 但 Fragment 则不行。

因此，您必须检索当前 Activity 的实例，这是我们通过 getActivity() 完成的。

如果你想在 Activity 中创建 Adapter 的实例，那么你可以通过简单地传递 this 来实现，就像我之前说的, Activity 可以强制转换为 Context 但 Fragment 则不行。所以 Activity 将被转换为 Context，但是当你想在 Fragment 中创建相同的内容时，你不能简单地传递 this，因此，它引发了一个错误。

正如您在评论中所说，现在还有另一个错误，那是因为您已经在该方法的第一行returned 了一些东西，因此，永远不会到达该方法下面的每一行，这就是为什么会出现该错误，请放置此行

return inflater.inflate(R.layout.fragment_home,container,false);

最后，错误将消失。

在您的方法中进行更多编辑后，您的 OnCreateView 将如下所示:

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

    view = inflater.inflate(R.layout.fragment_home, container, false); // Created a instance of View which we can return later.

    //cardview
    models = new ArrayList<>();
    models.add(new Model(R.drawable.brochure,"Brochure","Lorem ipsum dolor sit amet"));
    models.add(new Model(R.drawable.sticker,"Sticker","Lorem ipsum dolor sit amet"));
    models.add(new Model(R.drawable.poster,"Poster","Lorem ipsum dolor sit amet"));
    models.add(new Model(R.drawable.namecard,"Name Card","Lorem ipsum dolor sit amet"));

    adapter = new Adapter(models,this);

    viewPager = view.findViewById(R.id.viewPager); // Change getView() to view here.
    viewPager.setAdapter(adapter);
    viewPager.setPadding(130,0,130,0);

    return view; // Returned the view.
}