RecyclerView网格布局

GridLayoutManager

一、 引入问题

要实现这个布局，我们需要怎么做呢？

1. 用线性布局画各种长度尺寸的button?
   可行，但扩展性不够，假如将第二行和第三行互换位置呢 再增加几行呢 再增加几种类型的item呢？
   
   
2. 我们可以试下recyclerview的网格布局，进行动态适配各行的item
   可行，扩展性够
   
   

二、解决问题

方案：使用recyclerview的网格布局 

1. 定义itemType，针对不同的类型填充不同的布局

这里我们用不同itemType，之后可以在任意位置扩展这些类型的item

2. 核心代码

public class MainActivity extends AppCompatActivity { 
    private RecyclerView mRecyclerView; private RecyAdapter mAdapter; @Override protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mRecyclerView = findViewById(R.id.recycler_view); init(); } public void init() { 
    GridLayoutManager gridLayoutManager = new GridLayoutManager(getApplicationContext(), 3); mRecyclerView.setLayoutManager(gridLayoutManager); mAdapter = new RecyAdapter(); mRecyclerView.setAdapter(mAdapter); gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() { 
    @Override public int getSpanSize(int position) { 
    int itemViewType = mAdapter.getItemViewType(position); switch (itemViewType) { 
    case Constant.THREE_COLUME_ITEM_TYPE: return 3; case Constant.TWO_COLUME_ITEM_TYPE: return 2; default: return 1; } } }); mRecyclerView.addItemDecoration(new RecyclerView.ItemDecoration() { 
    @Override public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) { 
    super.getItemOffsets(outRect, view, parent, state); outRect.bottom = 30; outRect.left = 30; } }); } } 

public class RecyAdapter extends RecyclerView.Adapter { 
    private List<Integer> mData = new ArrayList<>(); public RecyAdapter() { 
    mData.add(0); mData.add(1); mData.add(2); mData.add(3); mData.add(4); mData.add(5); } @NonNull @Override public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) { 
    View view; int layoutId; switch (viewType) { 
    case Constant.THREE_COLUME_ITEM_TYPE: layoutId = R.layout.item_three_view_layout; break; case Constant.TWO_COLUME_ITEM_TYPE: layoutId = R.layout.item_two_view_layout; break; default: layoutId = R.layout.item_view_layout; break; } view = LayoutInflater.from(parent.getContext()).inflate(layoutId, parent, false); return new VH(view); } @Override public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) { 
    VH vh = (VH) holder; vh.mText.setText(mData.get(position) + ""); } @Override public int getItemCount() { 
    return mData.size(); } @Override public int getItemViewType(int position) { 
    switch (position) { 
    case 0: return Constant.THREE_COLUME_ITEM_TYPE; case 5: return Constant.TWO_COLUME_ITEM_TYPE; default: return Constant.ONE_COLUME_ITEM_TYPE; } } class VH extends RecyclerView.ViewHolder { 
    TextView mText; public VH(@NonNull View itemView) { 
    super(itemView); mText = itemView.findViewById(R.id.text); } } } 

public class Constant { 
    public static final int THREE_COLUME_ITEM_TYPE = 0; public static final int ONE_COLUME_ITEM_TYPE = 1; public static final int TWO_COLUME_ITEM_TYPE = 2; } 

三、实现效果