实现沉浸式状态栏，意思是可以activity状态栏的内容可以显示在状态栏。
相关控件都来自于Design support library；是属于Material Design的思想，包括CoordinatorLayout、AppBarLayout、CollapsingToolbarLayout、Toolbar，通过这几个就可以完美的实现。

注意要点：

1.新建values-19、values-21文件夹及styles.xml文件

• values/styles

<!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

    <style name="AppTheme.No" parent="AppTheme" />

• values-19、values-21/styles:

<style name="AppTheme.No" >
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
        <item name="android:windowTranslucentStatus">true</item>
    </style>

接下来就是activity的布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical">

    <android.support.design.widget.CoordinatorLayout
        android:id="@+id/coordinator_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.AppBarLayout
            android:id="@+id/appbar_layout"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

            <android.support.design.widget.CollapsingToolbarLayout
                android:id="@+id/collapsing_toolbar_layout"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:fitsSystemWindows="true"
                android:minHeight="?attr/actionBarSize"
                app:layout_scrollFlags="scroll|exitUntilCollapsed">

                <ImageView
                    android:id="@+id/img_collapsed"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:scaleType="centerCrop"
                    android:src="@drawable/time"
                    app:layout_collapseMode="parallax"
                    app:layout_collapseParallaxMultiplier="0.5" />

                <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.v7.widget.Toolbar>
            </android.support.design.widget.CollapsingToolbarLayout>

        </android.support.design.widget.AppBarLayout>

        <android.support.v4.widget.NestedScrollView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">

            <TextView
                android:id="@+id/tv_scroll_content"
                android:layout_width="match_parent"
                android:layout_height="match_parent" />

        </android.support.v4.widget.NestedScrollView>
    </android.support.design.widget.CoordinatorLayout>

</LinearLayout>

activity.java相关代码：

private void initView() {
        toolbar = findViewById(R.id.toolbar);
        collapsingToolbarLayout = findViewById(R.id.collapsing_toolbar_layout);
        imgCollapsed = findViewById(R.id.img_collapsed);

        toolbar.setTitle("AppBarLayout");
        toolbar.setNavigationIcon(R.drawable.btn_24_back_b_nor);

        collapsingToolbarLayout.setTitle("CollapsingToolbar");
        collapsingToolbarLayout.setContentScrimColor(ContextCompat.getColor(this, R.color.colorAccent));
        collapsingToolbarLayout.setStatusBarScrimColor(ContextCompat.getColor(this, R.color.colorAccent));

        setSupportActionBar(toolbar);
//        setImmerseLayout(toolbar);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });

        tvScrollContent = findViewById(R.id.tv_scroll_content);

//获取StatusBar高度，并设置给标题栏（Toolbar）
protected void setImmerseLayout(View view) {// view为标题栏
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
            Window window = getWindow();
            window.addFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
            int statusBarHeight = getStatusBarHeight(this.getBaseContext());
            view.setPadding(0, statusBarHeight, 0, 0);
        }
    }

    public int getStatusBarHeight(Context context) {
        int result = 0;
        int resourceId = context.getResources().getIdentifier("status_bar_height", "dimen",
                "android");
        if (resourceId > 0) {
            result = context.getResources().getDimensionPixelSize(resourceId);
        }
        return result;
    }

看了几篇相关的博文，然后自己亲自试着写了一下，遇到了一些问题，所以还是要实践一下。但还是有些模糊。有时间再理解一下。