今天整理我之前寫的程式碼，發現之前監聽CollapsingToolbarLayout的狀態的時候是通過監聽包裹CollapsingToolbarLayout著的AppBarLayout的OnOffsetChangedListener的方法來實現的。當時也是借鑑其他程式設計師的方法實現的，現在也不知道是哪個網址，沒辦法貼出來。下面是我實現的方法：

public abstract class AppBarLayoutStateChangeListener implements AppBarLayout.OnOffsetChangedListener{

    enum State{
        EXPANDED
 
,//展開
COLLAPSED,//摺疊
INTERMEDIATE//中間狀態
}
    private State mCurrentState = State.INTERMEDIATE;

    @Override
public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
        if (verticalOffset == 0) {
            if (mCurrentState != State.EXPANDED) {
                onStateChanged(appBarLayout, State.EXPANDED
 
);
            }
            mCurrentState = State.EXPANDED;
        } else if (Math.abs(verticalOffset) >= appBarLayout.getTotalScrollRange()) {
            if (mCurrentState != State.COLLAPSED) {
                onStateChanged(appBarLayout, State.COLLAPSED);
            }
            mCurrentState 
 
= State.COLLAPSED;
        } else {
            if (mCurrentState != State.INTERMEDIATE) {
                onStateChanged(appBarLayout, State.INTERMEDIATE);
            }
            mCurrentState = State.INTERMEDIATE;
        }
    }

    public abstract void onStateChanged(AppBarLayout appBarLayout, State state);
}

然後只要在程式碼中監聽即可

abl.addOnOffsetChangedListener(new AppBarLayoutStateChangeListener() {
    @Override
public void onStateChanged(AppBarLayout appBarLayout, State state) {
        switch (state){
            case EXPANDED:
                Log.v("CoordinatorLayout","EXPANDED");
                break;
            case COLLAPSED:
                Log.v("CoordinatorLayout","COLLAPSED");
                toolbar.setVisibility(View.VISIBLE);
                break;
            case INTERMEDIATE:
                Log.v("CoordinatorLayout","INTERMEDIATE");
                toolbar.setVisibility(View.INVISIBLE);
                break;
        }
    }
});

我的使用場景是做圖片摺疊然後狀態列的隱藏，背景展開狀態列顯示，並且不在圖片中顯示title，我們在使用CollapsingToolbarLayout的使用的時候有一個屬性app:titleEnabled="false"設定為false的時候就不會在圖片上顯示title，然後我通過上面監聽的方法AppBarLayout來控制toolbar的隱藏顯示，以下是我的部分佈局程式碼

<android.support.design.widget.AppBarLayout
android:id="@+id/abl"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">

    <android.support.design.widget.CollapsingToolbarLayout
android:id="@+id/ctl"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_scrollFlags="scroll|exitUntilCollapsed"
app:expandedTitleMarginStart="48dp"
app:expandedTitleMarginEnd="64dp"
app:titleEnabled="false"
app:statusBarScrim="@color/colorPrimaryDark"
app:contentScrim="@color/colorPrimaryDark">

        <ImageView
android:layout_width="match_parent"
android:layout_height="180dp"
android:src="@drawable/pic_1"
android:scaleType="centerCrop"
app:layout_collapseMode="parallax"/>

        <android.support.v7.widget.Toolbar
android:id="@+id/toolbar_four"
android:visibility="invisible"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_scrollFlags="scroll|enterAlways"
app:layout_collapseMode="pin">

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

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

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