Develop Reference

I am a new developer,when I changed the theme to Theme. Material3 during Android development, there was a problem with folding the title bar

When I changed the theme to Theme. Material3 during Android development, there was a problem with folding the ActionBar.ToolBar is blocked.
[enter image description here](https://i.stack.imgur.com/VAqlb.png)
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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:id="#+id/lin"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="?attr/mainbackground">
<com.google.android.material.appbar.AppBarLayout
android:id="#+id/app_bar"
android:layout_width="match_parent"
android:layout_height="180dp"
android:fitsSystemWindows="true">
<com.google.android.material.appbar.CollapsingToolbarLayout
android:id="#+id/collapsing"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
app:contentScrim="?attr/appbarcolor"
app:collapsedTitleGravity="center_horizontal"
app:expandedTitleTextColor="?android:attr/textColor"
app:layout_scrollFlags="scroll|exitUntilCollapsed"
app:statusBarScrim="#android:color/transparent"
app:title="注册并开始">
<ImageView
android:id="#+id/iv_image"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
android:scaleType="centerCrop"
android:src="?attr/mainbackground"
app:layout_collapseMode="parallax" />
<androidx.appcompat.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:contentInsetLeft="0dp"
app:contentInsetStart="0dp"
app:layout_collapseMode="pin"/>
</com.google.android.material.appbar.CollapsingToolbarLayout>
</com.google.android.material.appbar.AppBarLayout>
<androidx.core.widget.NestedScrollView
android:id="#+id/nested_scrollView"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior">
......
</androidx.core.widget.NestedScrollView>
</androidx.coordinatorlayout.widget.CoordinatorLayout>
Originally, I used NestScollView for areas other than AppBarLayout. I tried to change it to a separate xml, and found it invalid. I also tried to add android: fitsSystemWindows="true" to her, which is also invalid

Android collapsible toolbar not working

I'm trying to make a collapsible toolbar in android. I want the image to collapse when the user scrolls.
XML:
<?xml version="1.0" encoding="UTF-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/lib/com.mridulahuja.kudamm" xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.mridulahuja.kudamm.activities.ProductInfoActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">
<android.support.design.widget.CollapsingToolbarLayout
android:id="#+id/collapsing_toolbar"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
app:contentScrim="?attr/colorPrimary"
app:expandedTitleMarginEnd="64dp"
app:expandedTitleMarginStart="48dp"
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_scrollFlags="scroll|enterAlways"
app:layout_collapseMode="pin"
android:minHeight="20dp"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light" />
<ImageView
android:id="#+id/imageView"
android:layout_width="match_parent"
android:layout_height="200dp"
android:scaleType="centerCrop"
android:fitsSystemWindows="true"
app:layout_collapseMode="parallax"
android:src="#drawable/splash_background"
app:layout_scrollFlags="scroll|enterAlways|enterAlwaysCollapsed"
android:minHeight="100dp" />
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" />
</ScrollView>
</android.support.design.widget.CoordinatorLayout>
JAVA:
CollapsingToolbarLayout collapsingToolbar =
(CollapsingToolbarLayout) findViewById(R.id.collapsing_toolbar);
collapsingToolbar.setTitle("Title");
It shows me this on android studio:
But when I run it, it just shows me this:
I've even tried to use android.support.v4.widget.NestedScrollView instead of ScrollView but it didn't work either.
Any idea what I'm doing wrong ???

Change the height of NestedScrollView to Wrap_content instead of match_parent, it is occupyig entire screen. Hope that works for you.

CollapsingToolBarLayout has dual toolbar

I am having issues with implementing CollapsingToolbarLayout. I have this problem:
Yes, I've got to place the view in the layout, but it collapses below the original toolbar (or ActionBar for that matter) as shown in the image below. I have no idea how to fix this.
Thanks for any help. I am using Android Studio 2.1.1.
Here is my layout file:
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
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=".ArticleActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="200dp"
android:id="#+id/app_bar_layout"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.design.widget.CollapsingToolbarLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/collapsing_toolbar"
app:layout_scrollFlags="scroll|enterAlways"
android:fitsSystemWindows="true"
app:contentScrim="?attr/colorPrimary"
app:expandedTitleMarginStart="48dp"
app:expandedTitleMarginEnd="64dp">
<ImageView
android:layout_width="match_parent"
android:layout_height="200dp"
android:id="#+id/featuredImage"
android:src="#mipmap/ic_launcher"
android:scaleType="centerCrop"
android:fitsSystemWindows="true"
app:layout_collapseMode="parallax"
android:contentDescription="#string/article_image"/>
<android.support.v7.widget.Toolbar
android:id="#+id/tool_bar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_collapseMode="pin"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light"/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"
app:layout_scrollFlags="scroll|enterAlways"
app:layout_behavior="#string/appbar_scrolling_view_behavior">
<WebView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/article_container" />
</FrameLayout>
<android.support.design.widget.FloatingActionButton
android:id="#+id/share"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="#dimen/fab_margin"
android:src="#mipmap/ic_share_variant" />
</android.support.design.widget.CoordinatorLayout>

I found out where I went wrong. I had left out the theme statement in the manifest. All I had to do was add the line android:theme="AppTheme.NoActionBar" to my activity in the manifest.
However, this brought up two new issues:
The new ToolBar scrolls out of view (does not stick to the top.)
The back button that should lead me to my previous activity is gone. However, I'll ask this as a separate question if I do not get the solutions from researching.

Toolbar elevation/shadow (for pre lollipop) when using CollapsingToolbarLayout

Below is the code I am using to have a collapsing toolbar. It works. But at the same time I am trying to have toolbar elevation which is not working in pre lollipop devices, so I am trying to do that by applying a view with a shadow drawable. It works, but in this case, has an unintended effect as the shadow is visible all the time (see below)
I want the shadow to be visible only when only the toolbar is visible
Any advise?
<android.support.design.widget.CoordinatorLayout
android:id="#+id/main_content"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">
<android.support.design.widget.AppBarLayout
android:id="#+id/appbar"
android:layout_width="match_parent"
android:layout_height="256dp"
android:fitsSystemWindows="true"
android:theme="#style/ThemeOverlay.AppCompat.Dark.ActionBar">
<android.support.design.widget.CollapsingToolbarLayout
android:id="#+id/collapsingToolbarLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
app:contentScrim="?attr/colorPrimary"
app:expandedTitleMarginStart="72dp"
app:expandedTitleTextAppearance="#style/ExpToolbarTitleStyle"
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<RelativeLayout
android:id="#+id/backdrop"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/transparent"
android:fitsSystemWindows="true"
android:scaleType="centerCrop"
app:layout_collapseMode="parallax"
app:layout_scrollFlags="scroll|enterAlways">
<ImageView
android:id="#+id/backdropimg"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
android:scaleType="centerCrop"
android:src="#drawable/img"/>
<com.makeramen.roundedimageview.RoundedImageView
android:id="#+id/profPic"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="48dp"
android:layout_height="48dp"
android:layout_alignParentBottom="true"
android:layout_marginBottom="16dp"
android:layout_marginLeft="16dp"
android:scaleType="fitCenter"
android:src="#drawable/imgprf"
app:riv_border_color="#color/icons"
app:riv_border_width="2dip"
app:riv_corner_radius="30dip"
app:riv_mutate_background="true"
app:riv_oval="true"/>
</RelativeLayout>
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_collapseMode="pin"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light"/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<View
android:id="#+id/toolbar_shadow"
style="#style/ElevationFix"
app:layout_scrollFlags="exitUntilCollapsed"
android:layout_width="match_parent"
android:layout_height="6dp"/>
<android.support.v4.view.ViewPager .........
.........
.........
</android.support.design.widget.CoordinatorLayout>

This is a bug, you can find here is Assigend as Small-Priority to Chris Banes (Android Developer).
https://code.google.com/p/android/issues/detail?id=182083

I suggest you to add the custom shadow view as foreground in your fragment container.
i did same thing in my code like:
<android.support.v4.widget.NestedScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
**android:foreground="#drawable/header_shadow"**>
You can do one more thing put
<item name="header_shadow" type="drawable">#null</item>
attibute in value-21 style.xml and before api 21 add it into your styles.xml like this..
<item name="header_shadow" type="drawable">#drawable/bottom_shadow</item>

RecyclerView in CoordinatorLayout loses its top padding after orientation changes

I am using Support Design Library rev. 23.0.1 (and 22.2.1 as well). The problem is after activity orientation changes if RecyclerView (placed in fragment) has been scrolled, it loses its top padding which is probably equal to StatusBar Height + AppBar Height (as you see on a picture).
See this sample video for details
Here is my Activity layout
<android.support.design.widget.CoordinatorLayout
android:id="#+id/coordinatorLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">
<android.support.design.widget.AppBarLayout
android:id="#+id/discount_activity_app_bar_layout"
android:layout_width="match_parent"
android:layout_height="256dp"
app:layout_behavior="com.moskart.mosfake.widget.AppBarLayoutBehavior"
android:theme="#style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:fitsSystemWindows="true"
>
<android.support.design.widget.CollapsingToolbarLayout
android:id="#+id/collapsingToolbarLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:contentScrim="?attr/colorPrimary"
app:expandedTitleMarginStart="#dimen/expanded_toolbar_title_margin_start"
app:expandedTitleMarginBottom="96dp"
app:expandedTitleTextAppearance="#style/TextAppearance.Design.CollapsingToolbar.Expanded"
app:layout_scrollFlags="scroll|exitUntilCollapsed"
>
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/hero_image"
app:layout_collapseMode="parallax"
app:layout_collapseParallaxMultiplier="0.7"
android:fitsSystemWindows="true"
/>
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_collapseMode="pin"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light"
app:theme="#style/ThemeOverlay.AppCompat.Dark.ActionBar">
</android.support.v7.widget.Toolbar>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
app:behavior_overlapTop="64dp"
android:fitsSystemWindows="true" >
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/fragment"
android:name="com.moskart.mosfake.fragment.DiscountFeedFragment"
tools:layout="#layout/fragment_discount_feed"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</FrameLayout>
</android.support.design.widget.CoordinatorLayout>
And a simple fragment contains RecyclerView
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.moskart.mosfake.fragment.DiscountFeedFragment"
>
<com.moskart.mosfake.widget.GridRecyclerView
android:id="#+id/recycler_view_discount_feed"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
By the way, I found some following issues, but these answers doesn't solve my problem. I've also tried approaches described here and here, but it has no effect, or I doing something wrong.
Thanks for your help!