RecyclerView

超、凢脫俗 2022-07-13 05:07 153阅读 0赞

[RecyclerView优秀文集][RecyclerView]

![1460000007554167_w_976_h_252][]

# RecyclerView.ViewHolder #

![ViewHolder][]

# RecyclerView.Adapter #

![RecyclerView.Adapter][]

# LayoutManager #

## LinearLayoutManager ##

## GridLayoutManager ##

## StaggeredGridLayoutManager ##

![LayoutManager][]

# RecyclerView.ItemDecoration #

# RecyclerView.ItemAnimator #

## DefaultItemAnimator ##

# ItemTouchHelper #

# SnapHelper #

# RecyclerView.RecycledViewPool #

# CursorAdapter #

hold a CursorAdapter member in my recyclerView.Adapter implementation. Then passing all the handling of creating the new view & binding it to the cursor adapter

public class MyRecyclerAdapter extends Adapter<MyRecyclerAdapter.ViewHolder> { 
    
        // Because RecyclerView.Adapter in its current form doesn't natively 
        // support cursors, we wrap a CursorAdapter that will do all the job
        // for us.
        CursorAdapter mCursorAdapter;
    
        Context mContext;
    
        public MyRecyclerAdapter(Context context, Cursor c) {
    
            mContext = context;
    
            mCursorAdapter = new CursorAdapter(mContext, c, 0) {
    
                @Override
                public View newView(Context context, Cursor cursor, ViewGroup parent) {
                    // Inflate the view here
                }
    
                @Override
                public void bindView(View view, Context context, Cursor cursor) {
                    // Binding operations
                }
            };
        }
    
        public static class ViewHolder extends RecyclerView.ViewHolder { 
            View v1;
    
            public ViewHolder(View itemView) {
                super(itemView);
                v1 = itemView.findViewById(R.id.v1);
            }
        }
    
        @Override
        public int getItemCount() {
            return mCursorAdapter.getCount();
        }
    
        @Override
        public void onBindViewHolder(ViewHolder holder, int position) {
            // Passing the binding operation to cursor loader
            mCursorAdapter.getCursor().moveToPosition(position); //EDITED: added this line as suggested in the comments below, thanks :)
            mCursorAdapter.bindView(holder.itemView, mContext, mCursorAdapter.getCursor());
    
        }
    
        @Override
        public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            // Passing the inflater job to the cursor-adapter
            View v = mCursorAdapter.newView(mContext, mCursorAdapter.getCursor(), parent);
            return new ViewHolder(v);
        }
    }

# SimpleCursorAdapter参数之谜 #

简书作者：zzh0838，原文链接：[http://www.jianshu.com/p/daadc9d2bf1a][http_www.jianshu.com_p_daadc9d2bf1a]

## **Question** ##

SimpleCursorAdapter的构造函数是

SimpleCursorAdapter(Context context, int layout, Cursor c, String[] from, int[] to, int flags);

最后一个参数可选的值有：

*  FLAG\_AUTO\_REQUERY （这个值在Api 11 以后（包含）被弃用了，不用管）
 *  FLAG\_REGISTER\_CONTENT\_OBSERVER
 *  0

那到底应该选哪一个呢（虽然只是二选一）？没错，我懵逼了。这个时候，当然是google来帮忙，stackOverFlow搜一搜，but，but，but，搜到的内容都很简略，没人告诉我，我在写SimpleCursorAdapter的时候应该传哪一个参数。

## **Answer** ##

自己看源码喽,先看看继承继承关系吧（来至官方文档）：

java.lang.Object
       ↳    android.widget.BaseAdapter
            ↳    android.widget.CursorAdapter
                 ↳    android.widget.ResourceCursorAdapter
                      ↳    android.widget.SimpleCursorAdapter

好吧，先看看SimpleCursorAdapter的默认构造函数吧

public SimpleCursorAdapter(Context context, int layout, Cursor c, String[] from,
                int[] to, int flags) {
            super(context, layout, c, flags);
            mTo = to;
            mOriginalFrom = from;
            findColumns(c, from);
        }

可以看到flags传到了父类ResourceCursorAdapter的构造函数。那我们去看看吧。

public ResourceCursorAdapter(Context context, int layout, Cursor c, int flags) {
            super(context, c, flags);
            mLayout = mDropDownLayout = layout;
            mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            mDropDownInflater = mInflater;
        }

flags又传到父类CursorAdapter了，再去看看：

public CursorAdapter(Context context, Cursor c, int flags){
            init(context, c, flags);
    }

调用了init：

void init(Context context, Cursor c, int flags) {
            if ((flags & FLAG_AUTO_REQUERY) == FLAG_AUTO_REQUERY) {
                flags |= FLAG_REGISTER_CONTENT_OBSERVER;
                mAutoRequery = true;
            } else {
                mAutoRequery = false;
            }
            boolean cursorPresent = c != null;
            mCursor = c;
            mDataValid = cursorPresent;
            mContext = context;
            mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1;
            if ((flags & FLAG_REGISTER_CONTENT_OBSERVER) == FLAG_REGISTER_CONTENT_OBSERVER) {
                mChangeObserver = new ChangeObserver();
                mDataSetObserver = new MyDataSetObserver();
            } else {
                mChangeObserver = null;
                mDataSetObserver = null;
            }
    
            if (cursorPresent) {
                if (mChangeObserver != null) c.registerContentObserver(mChangeObserver);
                if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver);
            }
        }

函数有点长，假设我们的flags设置成了 0，不会有什么操作，假设我们的flags设置成了FLAG\_REGISTER\_CONTENT\_OBSERVER， 那么接下来会构造两个Observer:

mChangeObserver = new ChangeObserver();
    mDataSetObserver = new MyDataSetObserver();

并且在cursor不为null的时候将这两个Observer注册给cusor。

if (mChangeObserver != null) c.registerContentObserver(mChangeObserver);
    if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver);

那么问题来了，什么时候这两个Observer才会被触发呢？看看Cursor文档吧，文档了这么说的。

当调用方法requery()时，会触发ContentObserver。

当调用方法requery(), deactivate(), or close()时，DataSetObserver会被触发。

然后继续看文档，requery(), deactivate()都被弃用了。调用close后，cursor就没了（Closes the Cursor, releasing all of its resources and making it completely invalid.）。我尼玛，我尼玛，我尼玛，我心里一万只草泥马在奔腾，都不用看两个Observer定义的操作了。传这个参数压根就没什么鸟用。lz彻底懵逼了。

好了，现在可以下结论了：flag永远传0就可以了

[RecyclerView]: http://blog.csdn.net/axi295309066/article/details/52748508
[1460000007554167_w_976_h_252]: /images/20220713/689f63b0799e4e9aaedc72daeb7468ea.png
[ViewHolder]: /images/20220713/cf9b29c79a94466f9c20984f8b00193a.png
[RecyclerView.Adapter]: /images/20220713/f7541d8bd8194fd091a4d78b0c79e0cd.png
[LayoutManager]: /images/20220713/5a72d399ae4040459a1019cab9bdd764.png
[http_www.jianshu.com_p_daadc9d2bf1a]: http://www.jianshu.com/p/daadc9d2bf1a