1.佈局

<?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">

    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            <ImageView
                android:id="@+id/header"
                android:layout_width="match_parent"
                android:layout_height="@dimen/header_height" //圖片高度為200dp
                android:scaleType="centerCrop"
                android:src="@mipmap/header_img"/>

            <TextView
                style="@style/TextAppearance.AppCompat.Display2"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="Android支付寶支付整合\nAndroid支付寶支付整合Android支付寶\n支付整合Android支付寶支付整合"/>
        </LinearLayout>
    </android.support.v4.widget.NestedScrollView>


    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar_behavior"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:layout_behavior="liuwp.com.attendance.activity.ToolbarAlphaBehavior"
        />


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

2.實現自定義的ToolbarAlphaBehavior

public class ToolbarAlphaBehavior extends CoordinatorLayout.Behavior<Toolbar> {
    private static final String TAG = "ToolbarAlphaBehavior";
    private int offset = 0;
    private int startOffset = 0;
    private int endOffset = 0;
    private Context context;

    public ToolbarAlphaBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
    }

    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, Toolbar child, View directTargetChild, View target, int nestedScrollAxes) {
        return true;
    }


    @Override
    public void onNestedScroll(CoordinatorLayout coordinatorLayout, Toolbar toolbar, View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) {
        startOffset = 0;
        endOffset = context.getResources().getDimensionPixelOffset(R.dimen.header_height) - toolbar.getHeight();
        offset += dyConsumed;
        if (offset <= startOffset) {  //alpha為0
            toolbar.getBackground().setAlpha(0);
        } else if (offset > startOffset && offset < endOffset) { //alpha為0到255
            float precent = (float) (offset - startOffset) / endOffset;
            int alpha = Math.round(precent * 255);
            toolbar.getBackground().setAlpha(alpha);
        } else if (offset >= endOffset) {  //alpha為255
            toolbar.getBackground().setAlpha(255);
        }
    }

}
 

3. 給Toolbar配置behavior

 app:layout_behavior="com.xxx.activity.ToolbarAlphaBehavior" //新增配置

4.toolbar的透明初始化 在oncreate方法中

toolbar.getBackground().setAlpha(0);//toolbar透明度初始化為0