RecyclerView和ListView不同 ,是不自带分隔线的
如此:
在讲为Item加入分割线本质的前,先来介绍,认识一下ChildView,也就是平时我们用到的ListView
RecyclerView中的getChildAt(int position)这个返回的ChildView是哪一部分?
修改list_item的代码,添加一条
android:layout_margin = "10dp"
那么在RecyclerView中,Google为我们提供了RecyclerView.ItemDecoration添加分隔线
它是一个类,里面封装了三个方法:
(1)void getItemOffsets()
(2)void onDraw()
(3)void onDrawOver()
我们在创建自己的装饰类继承RecyclerView.ItemDecoration的时候,我们只要重写getItemOffsets(),还有onDraw()和onDrawOver两个其中之一就可以了。
那getItemOffsets()方法有什么用呢?从字面意思就是Item要偏移,由于我们在Item和Item之间加入了分隔线,线其实本质就是一个长方形,也是用户自定义的,既然线也有长宽高,就画横线来说,上面的项目加入了分隔线,那下面的项目就要往下平移,平移的量就是分隔线的高度。
我们自定义的MyDecoration.java :(继承RecyclerView.ItemDecoration)
public class MyDecoration extends RecyclerView.ItemDecoration{ private Context mContext; private Drawable mDivider; private int mOrientation; public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL; public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL; //我们通过获取系统属性中的listDivider来添加,在系统中的AppTheme中设置 public static final int[] ATRRS = new int[]{ android.R.attr.listDivider }; public MyDecoration(Context context, int orientation) { this.mContext = context; final TypedArray ta = context.obtainStyledAttributes(ATRRS); this.mDivider = ta.getDrawable(0); ta.recycle(); setOrientation(orientation); } //设置屏幕的方向 public void setOrientation(int orientation){ if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST){ throw new IllegalArgumentException("invalid orientation"); } mOrientation = orientation; } @Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { if (mOrientation == HORIZONTAL_LIST){ drawVerticalLine(c, parent, state); }else { drawHorizontalLine(c, parent, state); } } //画横线, 这里的parent其实是显示在屏幕显示的这部分 public void drawHorizontalLine(Canvas c, RecyclerView parent, RecyclerView.State state){ int left = parent.getPaddingLeft(); int right = parent.getWidth() - parent.getPaddingRight(); final int childCount = parent.getChildCount(); for (int i = 0; i < childCount; i++){ final View child = parent.getChildAt(i); //获得child的布局信息 final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)child.getLayoutParams(); final int top = child.getBottom() + params.bottomMargin; final int bottom = top + mDivider.getIntrinsicHeight(); mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); //Log.d("wnw", left + " " + top + " "+right+" "+bottom+" "+i); } } //画竖线 public void drawVerticalLine(Canvas c, RecyclerView parent, RecyclerView.State state){ int top = parent.getPaddingTop(); int bottom = parent.getHeight() - parent.getPaddingBottom(); final int childCount = parent.getChildCount(); for (int i = 0; i < childCount; i++){ final View child = parent.getChildAt(i); //获得child的布局信息 final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)child.getLayoutParams(); final int left = child.getRight() + params.rightMargin; final int right = left + mDivider.getIntrinsicWidth(); mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } } //由于Divider也有长宽高,每一个Item需要向下或者向右偏移 @Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { if(mOrientation == HORIZONTAL_LIST){ //画横线,就是往下偏移一个分割线的高度 outRect.set(0, 0, 0, mDivider.getIntrinsicHeight()); }else { //画竖线,就是往右偏移一个分割线的宽度 outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0); } } }现在用shape来编写一个分割线样式:
在drawable右键添加xml文件即可
<?xml version="1.0" encoding="utf-8"?> <shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle"> <gradient android:centerColor="#ff00ff00" android:endColor="#ff0000ff" android:startColor="#ffff0000" android:type="linear" /> <size android:height="3dp" /> </shape>这是一条渐变的分割线
在styles.xml的AppTheme中,设置listDivider为我们的divider.xml文件:
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<item name="android:listDivider">@drawable/divider</item>这样,我们将系统的listDivider设置成我们自定义的分隔线。
在主活动里这样添加我们自定义的分割线
recyclerView.addItemDecoration(new MyDecoration(this,MyDecoration.VERTICAL_LIST));
运行后如下