Android 滑动Toolbar透明度变化

一、这是效果

二、实现过程

       自定义ScrollView获取滑动量，然后转换为0--1的透明度，并改变Toolbar的setAlpha

三、实现代码

    MyScrollView.java

package com.xiaofan.test.view;import android.content.Context;import android.util.AttributeSet;import android.widget.ScrollView;public class MyScrollView extends ScrollView {    private TranslucentListener listener;    public void setListener(TranslucentListener listener) {        this.listener = listener;    }    public MyScrollView(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    protected void onScrollChanged(int l, int t, int oldl, int oldt) {        super.onScrollChanged(l, t, oldl, oldt);        if (listener != null) {            int scrollY = getScrollY();            int screen_height = getContext().getResources().getDisplayMetrics().heightPixels;            if (scrollY <= screen_height / 3f) {                //0~1f,透明度应该是1~0f                listener.onTranlucent(1 - scrollY / (screen_height / 3f));//划出去的高度/屏幕 高度/3f            }        }    }}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?><RelativeLayout 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">    <com.xiaofan.test.view.MyScrollView        android:id="@+id/scrollView"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:clipToPadding="false"        android:clipChildren="false"        android:paddingTop="?attr/actionBarSize">        <LinearLayout            android:layout_width="match_parent"            android:layout_height="match_parent"            android:orientation="vertical">            <Button                android:layout_width="match_parent"                android:layout_height="150dp"                android:text="哈哈哈1" />            <Button                android:layout_width="match_parent"                android:layout_height="150dp"                android:text="哈哈哈2" />            <Button                android:layout_width="match_parent"                android:layout_height="150dp"                android:text="哈哈哈3" />            <Button                android:layout_width="match_parent"                android:layout_height="150dp"                android:text="哈哈哈4" />            <Button                android:layout_width="match_parent"                android:layout_height="150dp"                android:text="哈哈哈5" />            <Button                android:layout_width="match_parent"                android:layout_height="150dp"                android:text="哈哈哈6" />        </LinearLayout>    </com.xiaofan.test.view.MyScrollView>    <android.support.v7.widget.Toolbar        android:id="@+id/toolbar"        android:layout_width="match_parent"        android:layout_height="?attr/actionBarSize"        android:background="?attr/colorPrimary"        app:title="哈哈哈哈哈哈哈" /></RelativeLayout>

MainActivity

package com.xiaofan.test;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.support.v7.widget.Toolbar;import android.util.Log;import com.xiaofan.test.view.MyScrollView;import com.xiaofan.test.view.TranslucentListener;public class MainActivity extends AppCompatActivity implements TranslucentListener {    private Toolbar toolbar;    private MyScrollView scrollView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        toolbar = (Toolbar) findViewById(R.id.toolbar);        scrollView = (MyScrollView) findViewById(R.id.scrollView);        scrollView.setListener(this);        setSupportActionBar(toolbar);    }    @Override    public void onTranlucent(float alpha) {        toolbar.setAlpha(alpha);    }}

TranslucentListener

public interface TranslucentListener {
     void onTranlucent(float alpha);
}

注意：想实现内容不考虑padding需添加

           android:clipToPadding="false"    该绘制的时候考不考虑padding  false考虑padding
       android:clipChildren="false   子控件是否不超出padding的区域