大家好，又见面了，我是你们的朋友全栈君。
ListView是我们在开发Android程序时用得比较多的一种widget，通常用来展示多条数据，这里，我对ListView的一些功能点作一个简单介绍。
1. Cache color hint
但是，由于系统默认的cache color hint的颜色是#191919，当你滑动ListView时，你就会看到一个黑色的背景。
出现这种情况肯定是不正确的，那么怎么解决呢？
最简单的方法是将cache color hint设置为透明。
android:cacheColorHint=”#00000000″ 或 setCacheColorHint(Color.TRANSPARENT)
以下是官方文档的原文：
As mentioned before, ListView has a transparent/translucent background by default, and so all default widgets in the Android UI toolkit. This implies that when ListView redraws its children, it has to blend the children with the window’s background. Once again, this requires costly readbacks from memory that are particularly painful during a scroll or a fling when drawing happens dozen of times per second.
To improve drawing performance during scrolling operations, the Android framework reuses the cache color hint. When this hint is set, the framework copies each child of the list in a Bitmap filled with the hint value (assuming that another optimization, called scrolling cache, is not turned off). ListView then blits these bitmaps directly on screen and because these bitmaps are known to be opaque, no blending is required. Also, since the default cache color hint is #191919, you get a dark background behind each item during a scroll.
To fix this issue, all you have to do is either disable the cache color hint optimization, if you use a non-solid color background, or set the hint to the appropriate solid color value. You can do this from code (see setCacheColorHint(int)) or preferably from XML, by using the android:cacheColorHint attribute. To disable the optimization, simply use the transparent color #00000000. The following screenshot shows a list with android:cacheColorHint=”#00000000″ set in the XML layout file.
2. Divider
3. ListView绘制顺序
由于通过情况下，listview的item的背景是透明的，所以，当用户按下一个item时，黄色的selector就会透出来。假如你的item是一个TextView，你将其背景设置为白色，那么当按钮一个item是时，selector就不会显示出来了，因为它是绘制在所有item的下面。
所以，对于ListView来说，其绘制顺序是：
Background -> Dividers -> List selector -> Itemviews
4. OnItemClickListener不触发
android:descendantFocusability=”blocksDescendants”即可，这样Item Layout就屏蔽了所有子控件获取Focus的权限，不需要针对Item Layout中的每一个控件重新设置focusable属性了，如此就可以顺利的响应onItemClickListener中的onItemClick()方法了。
...
case MotionEvent.ACTION_UP: {
switch (mTouchMode) {
case TOUCH_MODE_DOWN:
case TOUCH_MODE_TAP:
case TOUCH_MODE_DONE_WAITING:
final int motionPosition = mMotionPosition;
final View child = getChildAt(motionPosition - mFirstPosition);
final float x = ev.getX();
final boolean inList = x > mListPadding.left
&& x < getWidth() - mListPadding.right;
if (child != null && !child.hasFocusable() && inList) {
if (mTouchMode != TOUCH_MODE_DOWN) {
child.setPressed(false);
}
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
...
android:descendantFocusability=”blocksDescendants”
public static final int descendantFocusability
| Constant | Value | Description |
| beforeDescendants | 0 | The ViewGroup will get focus before any of its descendants. |
| afterDescendants | 1 | The ViewGroup will get focus only if none of its descendants want it. |
| blocksDescendants | 2 | The ViewGroup will block its descendants from receiving focus. |
注意：
还有一种情况也会导致OnItemClickListener或OnItemLongClickListener回调不会执行，那就是ListView的child设置了onClickListener或onLongClickListener。我们可以通过源代码看出，在你调用setOnClickListener()方法后，它会调用setClickable(true)，在onTouchEvent里面的实现如下：
if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) { // .... return true;}当一个View在onTouchEvent里面返回true后，ListView就不会正常接收到事件。
5. ListView不要做的事
有时候我们很容易让ListView的高度是wrap_content，这样做，很容易导致性能问题，wrap_content意味着as big as my children，这会导致1）测量大量的children；2）当添加child时，容易引起ListView重新发生layout，这又可能引发child的layout。我曾经遇到过一个问题，就是在维护别的写的代码时，ListView上下滑动速度特别慢，我把adapter等地方都优化完后，仍然一样，最终才发现ListView的高度是wrap_content，我把其改为match_parent之后，性能一下就正常了。
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