片段中的Android Studio RecyclerView [重复]

Question

我有这段代码，它在Fragment 中集成了一个RecyclerView，但是这一行：

RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager (this, 3);

给我一​​个错误，它告诉我：

GridLayoutManager中的GridLayoutManager(android.content.Context,int)不能应用到(com.example.julianrc1.petracecitm.PerdidosGaleria_Fragment,int)

我不知道为什么，有什么想法吗？

这是我正在使用的代码：

package com.example.julianrc1.petracecitm;

import android.content.res.Resources;
import android.graphics.Rect;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.util.TypedValue;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;
import java.util.List;

public class PerdidosGaleria_Fragment extends Fragment {

    private RecyclerView recyclerView;
    private AnunciosAdapter adapter;
    private List<Anuncio> anuncioList;

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

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_perdidosgaleria, container, false);
        Toolbar toolbar = (Toolbar) rootView.findViewById(R.id.toolbar);
        ((AppCompatActivity)getActivity()).setSupportActionBar(toolbar);

        //initCollapsingToolbar();

        recyclerView = (RecyclerView)  rootView.findViewById(R.id.content_main);

        anuncioList = new ArrayList<>();
        adapter = new AnunciosAdapter(this, anuncioList);

        RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(this, 3);//columnas que quieres por filas
        recyclerView.setLayoutManager(mLayoutManager);
        recyclerView.addItemDecoration(new GridSpacingItemDecoration(2, dpToPx(10), true));
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setAdapter(adapter);

        prepareAlbums();

        try {
          //  Glide.with(this).load(R.drawable.cover).into((ImageView) rootView.findViewById(R.id.backdrop));
        } catch (Exception e) {
            e.printStackTrace();
        }


        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_perdidosgaleria, container, false);
    }
/*
    private void initCollapsingToolbar() {

        final CollapsingToolbarLayout collapsingToolbar =
                (CollapsingToolbarLayout) findViewById(R.id.collapsing_toolbar);
        collapsingToolbar.setTitle(" ");
        AppBarLayout appBarLayout = (AppBarLayout) findViewById(R.id.appbar);
        appBarLayout.setExpanded(true);

        // hiding & showing the title when toolbar expanded & collapsed
        appBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
            boolean isShow = false;
            int scrollRange = -1;

            @Override
            public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
                if (scrollRange == -1) {
                    scrollRange = appBarLayout.getTotalScrollRange();
                }
                if (scrollRange + verticalOffset == 0) {
                    collapsingToolbar.setTitle(getString(R.string.app_name));
                    isShow = true;
                } else if (isShow) {
                    collapsingToolbar.setTitle(" ");
                    isShow = false;
                }
            }
        });
    }
*/
    /**
     * Adding few albums for testing
     */
    private void prepareAlbums() {
        int[] covers = new int[]{
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon,
                R.drawable.icon};

        Anuncio a = new Anuncio("True Romance", 13, covers[0]);
        anuncioList.add(a);

        a = new  Anuncio("Xscpae", 8, covers[1]);
        anuncioList.add(a);

        a = new  Anuncio("Maroon 5", 11, covers[2]);
        anuncioList.add(a);

        a = new  Anuncio("Born to Die", 12, covers[3]);
        anuncioList.add(a);

        a = new  Anuncio("Honeymoon", 14, covers[4]);
        anuncioList.add(a);

        a = new  Anuncio("I Need a Doctor", 1, covers[5]);
        anuncioList.add(a);

        a = new  Anuncio("Loud", 11, covers[6]);
        anuncioList.add(a);

        a = new  Anuncio("Legend", 14, covers[7]);
        anuncioList.add(a);

        a = new  Anuncio("Hello", 11, covers[8]);
        anuncioList.add(a);

        a = new  Anuncio("Greatest Hits", 17, covers[9]);
        anuncioList.add(a);

        adapter.notifyDataSetChanged();
    }

    /**
     * RecyclerView item decoration - give equal margin around grid item
     */
    public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {

        private int spanCount;
        private int spacing;
        private boolean includeEdge;

        public GridSpacingItemDecoration(int spanCount, int spacing, boolean includeEdge) {
            this.spanCount = spanCount;
            this.spacing = spacing;
            this.includeEdge = includeEdge;
        }

        @Override
        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
            int position = parent.getChildAdapterPosition(view); // item position
            int column = position % spanCount; // item column

            if (includeEdge) {
                outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

                if (position < spanCount) { // top edge
                    outRect.top = spacing;
                }
                outRect.bottom = spacing; // item bottom
            } else {
                outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
                if (position >= spanCount) {
                    outRect.top = spacing; // item top
                }
            }
        }
    }

    /**
     * Converting dp to pixel
     */
    private int dpToPx(int dp) {
        Resources r = getResources();
        return Math.round(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics()));
    }
}

Answer 1

将 this 更改为 getActivity() ，因为您在 Fragment 中使用了 recyclerView。

• this 是 Activity 的上下文。
• getActivity() 是 Fragment 的上下文。

代码：

  RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(this, 3); 

到

 RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(getActivity(), 3); 

Answer 2

请在new GridLayoutManager(getActivity(), 3) 中使用getActivity() 而不是new GridLayoutManager(this, 3)

原因：GridLayoutManager(Context context, int spanCount) 在第一个参数中需要一个 Context 类型的实例，第二个参数需要一个跨度计数。

当你使用this 时，你传递的是一个 Fragment 实例，这不是传递的正确参数。

乐于助人。

Answer 3

Fragment类不扩展Context类的主要原因

java.lang.Object
   ↳    android.app.Fragment

并且Activity 类有一个上下文

java.lang.Object
   ↳    android.content.Context
       ↳    android.content.ContextWrapper
           ↳    android.view.ContextThemeWrapper
               ↳    android.app.Activity

这就是为什么当你使用this 时它会在活动中起作用而在片段中不起作用

那么你需要在片段中使用getActivity() 而不是this 来传递上下文

Answer 4

您必须更改以下内容：- 您不能使用片段代替上下文，因为片段不扩展上下文。但是 Activity 扩展了上下文。

您可以使用 getActivity()，它返回与片段关联的活动。 Activity 是一个上下文（因为 Activity 扩展了 Context）。

  RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(this, 3);

到

 RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(getActivity(), 3);

Answer 5

改变

new GridLayoutManager(this, 3)

到：

new GridLayoutManager(getActivity(), 3)