滑动显示隐藏ToolBar

 <android.support.design.widget.CoordinatorLayout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:sct="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

     <android.support.v4.widget.NestedScrollView
        ……/>

    <LinearLayout
        android:id="@+id/llTitle"
        android:layout_width="match_parent"
        android:layout_height="@dimen/dm_75"
        android:background="@android:color/transparent"
        android:orientation="vertical"
        android:paddingTop="@dimen/dm_25">

        <android.support.v7.widget.Toolbar
            android:id="@+id/alphaToolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@android:color/transparent"
            android:visibility="gone"
            app:popupTheme="@style/AppTheme.PopupOverlay"
            app:titleTextColor="@color/white">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:singleLine="true"
                android:text="@string/home_title"
                android:textColor="@color/white"
                android:textSize="18dp" />
        </android.support.v7.widget.Toolbar>
    </LinearLayout>
  </android.support.design.widget.CoordinatorLayout>

在代码中设置监听事件进行滑动显示隐藏

   mScroll.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
        @Override
        public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
            int toolbarHeight = llTitle.getHeight();
            //当滑动的距离 <= toolbar高度的时候，改变Toolbar背景色的透明度，达到渐变的效果
            if (mScroll.getScrollY() <= toolbarHeight) {
                float scale = (float) mScroll.getScrollY() / toolbarHeight;
                float alpha = scale * 255;
                llTitle.setBackgroundColor(Color.argb((int) alpha, 128, 0, 0));
                alphaToolbar.setVisibility(View.GONE);
            } else {
                //上述虽然判断了滑动距离与toolbar高度相等的情况，但是实际测试时发现，标题栏的背景色
                //很少能达到完全不透明的情况，所以这里又判断了滑动距离大于toolbar高度的情况，
                //将标题栏的颜色设置为完全不透明状态
                llTitle.setBackgroundResource(R.color.colorPrimary);
                alphaToolbar.setVisibility(View.VISIBLE);
            }
        }
    });