DiffUtils实现partial bindData

                                                                               DiffUtils实现partial bindData

support-v7:24.2.0中出来的一个兼容工具，它用来比较两个数据集，寻找出旧数据集-》新数据集的最小变化量。

这个工具对于列表中需要局部内容发生变化是时，只需要计算出发生变化的部分，只刷新变化部分的内容，即可极大的提高刷新页面数据的效率问题。不必通过notifyDataSetChanged方法进行整个界面的刷新

DiffUtil的作用，就是找出集合中每一个Item发生的变化，然后对每个变化给予对应的刷新。

1.先看DiffUtil.Callback这个抽象内的源码入下：

/** * A Callback class used by DiffUtil while calculating the diff between two lists. */public abstract static class Callback {    /**     * Returns the size of the old list.     *     * @return The size of the old list.     */    public abstract int getOldListSize();    /**     * Returns the size of the new list.     *     * @return The size of the new list.     */    public abstract int getNewListSize();    /**     * Called by the DiffUtil to decide whether two object represent the same Item.     * <p>     * For example, if your items have unique ids, this method should check their id equality.     *     * @param oldItemPosition The position of the item in the old list     * @param newItemPosition The position of the item in the new list     * @return True if the two items represent the same object or false if they are different.     */    public abstract boolean areItemsTheSame(int oldItemPosition, int newItemPosition);    /**     * Called by the DiffUtil when it wants to check whether two items have the same data.     * DiffUtil uses this information to detect if the contents of an item has changed.     * <p>     * DiffUtil uses this method to check equality instead of {@link Object#equals(Object)}     * so that you can change its behavior depending on your UI.     * For example, if you are using DiffUtil with a     * {@link android.support.v7.widget.RecyclerView.Adapter RecyclerView.Adapter}, you should     * return whether the items' visual representations are the same.     * <p>     * This method is called only if {@link #areItemsTheSame(int, int)} returns     * {@code true} for these items.     *     * @param oldItemPosition The position of the item in the old list     * @param newItemPosition The position of the item in the new list which replaces the     *                        oldItem     * @return True if the contents of the items are the same or false if they are different.     */    public abstract boolean areContentsTheSame(int oldItemPosition, int newItemPosition);    /**     * When {@link #areItemsTheSame(int, int)} returns {@code true} for two items and     * {@link #areContentsTheSame(int, int)} returns false for them, DiffUtil     * calls this method to get a payload about the change.     * <p>     * For example, if you are using DiffUtil with {@link RecyclerView}, you can return the     * particular field that changed in the item and your     * {@link android.support.v7.widget.RecyclerView.ItemAnimator ItemAnimator} can use that     * information to run the correct animation.     * <p>     * Default implementation returns {@code null}.     *     * @param oldItemPosition The position of the item in the old list     * @param newItemPosition The position of the item in the new list     *     * @return A payload object that represents the change between the two items.     */    @Nullable    public Object getChangePayload(int oldItemPosition, int newItemPosition) {        return null;    }}

2.使用方法：

 1.新建一个类继承DiffUtil.Callback实现抽象方法（前4个必须，最后一个可选）

  2.

//比较新老数据的差异

DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new DiffCallBack(mDatas, newDatas), true);//然后利用DiffUtil.DiffResult对象的dispatchUpdatesTo（）方法，传入RecyclerView的Adapter，替代mAdapter.notifyDataSetChanged()方法。diffResult.dispatchUpdatesTo(mAdapter);//将新数据添加适配器中

mMyAdapter.setList(newList);

举例说明：

需求：如下图：

 点击===》关注，实现点击条目的局部数据更新

  核心代码如下：

  DiffUtil.Callback的子类：

Adapter的代码

list_item.xml

MainActivity代码如下：

轻松实现列表数据的partial binddata~~~