一、机制
ListView机制 -先执行getCount，然后执行getView。如果getCount返回0，不执行getView
Gallery convertView不会复用，每次都返回NULL
二、问题整理
ListView最下面一个item没有横线（Divider）？
listview的布局高使用wrap_content，应该使用fill_parent
去除行与行之间的黑线：
List.setDivider(null);
切记ListView高度不能设置成wrap_content
会导致多次整个页面刷新
动态修改Item高度 – ItemRootView.getLayoutParams().height = heightValue;
尝试使用margin、Child height都无效
Item Root设置高度失效，可以通过设置子视图高度解决。（ListView ItemView 子视图设置margin无效）
两层，内层使用margin，外层使用FrameLayout失效，改成Linearlayout有效。例如Htc G12 就会失效。
三、常用属性
ListView Item selector
item.xml 外层LinearLayout设置selector.xml后，内层再设置bakcground没有选中效果。
因为点击后下层其实改变了，但是被上层给盖住了，，这是常识。。。。。
点击父视图，子视图是否被选中，例如button
去除选中时的黄色底色android:listSelector="#00000000"
android:listSelector="@null" // 这样设置无效
1. 是否显示ScrollBar
2. 关闭OverScroll ， 有些手机上OverScroll有类似FadingEdge效果
listView.setOverScrollMode(View.OVER_SCROLL_NEVER);
3. 去除拖动时默认的黑色背景：android:cacheColorHint="#00000000"
5. ListView刷新后自动滚到最底部：List.setSelection(msgList.getAdapter().getCount()-1);6. 去除ListView滑到顶部和底部时边缘的黑色阴影：android:fadingEdge="none"
** 异常
get item type 从0开始，出现以下异常说明，getItemViewType 返回类型个数超过getViewTypeCount。
当前异常是getItemViewType 返回3种类型的id，而getViewTypeCount = 2
java.lang.ArrayIndexOutOfBoundsException: length=2; index=2 at android.widget.AbsListView$RecycleBin.addScrapView(AbsListView.java:7188) at android.widget.ListView.measureHeightOfChildren(ListView.java:1338) at android.widget.ListView.onMeasure(ListView.java:1238) at android.view.View.measure(View.java:15729) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4854) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404) at android.widget.LinearLayout.measureVertical(LinearLayout.java:695) at android.widget.LinearLayout.onMeasure(LinearLayout.java:588) at android.view.View.measure(View.java:15729) at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:645) at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:425) at android.view.View.measure(View.java:15729) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4854) at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) at android.view.View.measure(View.java:15729) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4854) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404) at android.widget.LinearLayout.measureVertical(LinearLayout.java:695) at android.widget.LinearLayout.onMeasure(LinearLayout.java:588) at android.view.View.measure(View.java:15729) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4854) at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2344) at android.view.View.measure(View.java:15729) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1948) at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1104) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1300) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4498) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749) at android.view.Choreographer.doCallbacks(Choreographer.java:562) at android.view.Choreographer.doFrame(Choreographer.java:532) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735) at android.os.Handler.handleCallback(Handler.java:725) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:5105) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) at dalvik.system.NativeStart.main(Native Method)
onScroll 滚动状态判断
onScrollListener
SCROLL_STATE_IDLE 滑动后静止SCROLL_STATE_FLING 手指离开屏幕后，惯性滑动SCROLL_STATE_TOUCH_SCROLL 手指在屏幕上滑动
测试相关
ActivityThread中代码，此代码调用onSaveInstanceState。mInstrumentation负责调用on***方法
mInstrumentation.callActivityOnSaveInstanceState(r.activity, state);
GridVie 不显示滚动条
android:scrollbars="none"与
setVerticalScrollBarEnabled(true);
挫折其实就是迈向成功所应缴的学费。
