使用過ListView滴小夥伴都知道。ListView有這樣一個屬性android:divider，用來設置每一個item之間切割線滴屬性。問題來了，那麽RecyclerView這個控件有沒有這個屬性呢，嘗試了一下，沒有這個屬性。可是RecyclerView有這種方法mLinearRecycler.addItemDecoration()，用來加入切割線滴。以下是這部分源代碼：

public static abstract class ItemDecoration {

public void onDraw(Canvas c, RecyclerView parent, State state) 
{
            onDraw(c, parent);
}

public
 
 void onDrawOver(Canvas c, RecyclerView parent, State state) 
{
            onDrawOver(c, parent);
}
 @Deprecated
public void getItemOffsets(Rect outRect, int itemPosition,RecyclerView parent) 
{
            outRect.set(0, 0, 0, 0);
}

public void getItemOffsets(Rect outRect, View view,RecyclerView parent, State state) 
{
     getItemOffsets(outRect, ((LayoutParams)view.getLayoutParams()).getViewLayoutPosition(), parent);
}
    }
 

RecyclerView在調用addItemDecoration()滴時候就會去繪制decoration，通過源代碼我們會發現，會調用裏面的onDraw()和onDrawOver()方法。而getItemOffsets()，是為每一個Item設置一定的偏移量。主要用於繪制decorator。

以下我們來看一下該類的實現，代碼例如以下：

    package recyclerview.hy.com.myrecyclerview.decoration;

    import android.content.Context;
    import android.graphics.Canvas;
    import
 
 android.graphics.Rect;
    import android.graphics.drawable.Drawable;
    import android.support.v7.widget.LinearLayoutManager;
    import android.support.v7.widget.RecyclerView;
    import android.view.View;

    import recyclerview.hy.com.myrecyclerview.R;

    /**
     * Created by Ying on 2016/2/16.
     */
    public class ListItemDecoration extends RecyclerView.ItemDecoration {

    private Drawable mDrawable;

    private final static int DEFAULT_ORENTATION = LinearLayoutManager.VERTICAL;

    private int mOrientation;

    public ListItemDecoration(Context context, int orientation) {
        if (orientation != LinearLayoutManager.HORIZONTAL && orientation != LinearLayoutManager.VERTICAL) {
            //方法一：假設沒設置布局顯示方向，默認設置為垂直方向
            this.mOrientation = DEFAULT_ORENTATION;
            //方法二：拋出異常，提示設置布局方向
           // throw new IllegalArgumentException("invalid orientation");
        } else {
            this.mOrientation = orientation;
        }
        //設置切割線樣式
        mDrawable = context.getResources().getDrawable(R.drawable.divider);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        if (mOrientation == LinearLayoutManager.HORIZONTAL) {
            drawHorizontal(c, parent);
        } else {
            drawVertical(c, parent);
        }
    }

    private void drawHorizontal(Canvas c, RecyclerView parent) {
        int top = parent.getPaddingTop();
        int bottom = parent.getHeight() - parent.getPaddingBottom();
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)child.getLayoutParams();
            int left = child.getRight() + params.rightMargin;
            int right = left + mDrawable.getIntrinsicHeight();
            mDrawable.setBounds(left, top, right, bottom);
            mDrawable.draw(c);
        }
    }

    private void drawVertical(Canvas c, RecyclerView parent) {
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
            android.support.v7.widget.RecyclerView v = new android.support.v7.widget.RecyclerView(parent.getContext());
            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            int top = child.getBottom() + params.bottomMargin;
            int bottom = top + mDrawable.getIntrinsicHeight();
            mDrawable.setBounds(left, top, right, bottom);
            mDrawable.draw(c);
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        if (mOrientation == DEFAULT_ORENTATION) {
            outRect.set(0, 0, 0, mDrawable.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDrawable.getIntrinsicWidth(), 0);
        }
    }
    }

這樣就實現了切割線的類，我們僅僅要在Activity中加入這樣一句話就可以：

mLinearRecycler.addItemDecoration(new ListItemDecoration(this, LinearLayoutManager.VERTICAL));

看一下效果圖：

假設你想設置其他樣式滴切割線僅僅需在這句話進行改動：

 mDrawable = context.getResources().getDrawable(R.drawable.divider);

關於RecyclerView實現GridView和瀑布流效果就不在貼代碼了。這些代碼demo裏面有。

看一下效果圖：
GridView：

瀑布流：

關於瀑布流背景點擊變色，假設有疑惑，能夠參考我滴還有一篇博客Android之簡單改變button顏色方案。

項目代碼：demo下載地址
如有疑問。記得給我留言哦~技術交流嘛~~喜歡滴，頂一下唄！

Android之RecyclerView簡單使用(三)