1、启动白屏、黑屏
给启动页设置Theme，看起来就像秒启动了。
<style name="SplashTheme" parent="Theme.AppCompat.NoActionBar">
<item name="android:windowFullscreen">true</item>
<item name="android:windowBackground">@mipmap/splash</item>
</style>
一般启动页也就一张图片，直接设置了android:windowBackground就可以，imageview都不用了。
2、ViewStub
A ViewStub is an invisible, zero-sized View that can be used to lazily inflate layout resources at runtime.
比如加载列表空布局、引导提示等。
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.wangsz.myapplication.MainActivity">
<TextView
android:id="@+id/textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Toggle"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"/>
<ViewStub
android:id="@+id/viewstub"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inflatedId="@+id/viewstub_layout"
android:layout="@layout/viewstub_layout" />
</android.support.constraint.ConstraintLayout>
android:layout="@layout/viewstub_layout" ---ViewStub本身被替换掉的布局文件，调用viewStub.inflate()。
android:inflatedId="@+id/viewstub_layout" ---ViewStub被提替换之后的布局的id
替换之后的布局的长宽还是以viewstub的属性为准：
android:layout_width="wrap_content"
android:layout_height="wrap_content"
- viewstub本身的setVisibility方法，在调用的时候会判断是否inflate()，如果是第一次，则会设置viewstub本身的visibility，并且调用inflate()，当再次调用setVisibility方法的时候，只会设置替换之后的view的visibility，所以viewstub的getVisibility()只会等于第一次设置之后的visibility。
/**
* When visibility is set to {@link #VISIBLE} or {@link #INVISIBLE},
* {@link #inflate()} is invoked and this StubbedView is replaced in its parent
* by the inflated layout resource. After that calls to this function are passed
* through to the inflated view.
*
* @param visibility One of {@link #VISIBLE}, {@link #INVISIBLE}, or {@link #GONE}.
*
* @see #inflate()
*/
@Override
@android.view.RemotableViewMethod
public void setVisibility(int visibility) {
if (mInflatedViewRef != null) {
View view = mInflatedViewRef.get();
if (view != null) {
view.setVisibility(visibility);
} else {
throw new IllegalStateException("setVisibility called on un-referenced view");
}
} else {
super.setVisibility(visibility);
if (visibility == VISIBLE || visibility == INVISIBLE) {
inflate();
}
}
}
这段代码，viewStub指向的layout会在第一次点击textView的时候显示，然后之后的所有点击都是消失，因为一开始viewStub.getVisibility() == View.GONE，第一次调用的viewStub.setVisibility(View.VISIBLE);之后viewStub.getVisibility()的值就一直等于View.VISIBLE，调用viewStub.setVisibility(View.INVISIBLE)只会控制指向的layout的显示，不会改变viewStub的属性。
- java.lang.IllegalStateException: ViewStub must have a non-null ViewGroup viewParent
对ViewStub的inflate操作只能进行一次，因为inflate的时候是将其指向的布局文件解析inflate并替换掉当前ViewStub本身（由此体现出了ViewStub“占位符”性质），一旦替换后，此时原来的布局文件中就没有ViewStub控件了，因此，如果多次对ViewStub进行infalte，会出现错误信息：ViewStub must have a non-null ViewGroup viewParent。
比如：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.textview);
viewStub = (ViewStub) findViewById(R.id.viewstub);
textView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.i("viewStub",viewStub.getVisibility() + "");
if (viewStub.getVisibility() == View.VISIBLE){
View view = viewStub.inflate();
viewStub.setVisibility(View.INVISIBLE);
} else {
viewStub.setVisibility(View.VISIBLE);
}
}
});
}
第二次点击textview就会报错，应为第一次调用viewStub.setVisibility(View.VISIBLE)的时候已经调用过一次inflate()。
