android scrollview上滑显示标题

一，common_change_color - 渐变背景色

<?xml version="1.0" encoding="utf-8"?>

android:angle="0"

android:centerX="0.5"

android:centerY="0.5"

android:endColor="#FF6461"

android:startColor="#ff9b78"

android:type="linear" />

</shape>

二，MyScrollView - 主要获取y轴的滑动距离

package com.example.thinkpad.demo2.ui;

import android.content.Context;

import android.util.AttributeSet;

import android.widget.ScrollView;

public class MyScrollViewextends ScrollView {

private OnScrollListenerlistener;

public void setOnScrollListener(OnScrollListener listener) {

this.listener = listener;

}

public MyScrollView(Context context) {

super(context);

}

public MyScrollView(Context context, AttributeSet attrs) {

super(context, attrs);

}

public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {

super(context, attrs, defStyleAttr);

}

//设置接口

public interface OnScrollListener{

void onScroll(int scrollY);

}

//重写原生onScrollChanged方法，将参数传递给接口，由接口传递出去

@Override

protected void onScrollChanged(int l, int t, int oldl, int oldt) {

super.onScrollChanged(l, t, oldl, oldt);

if(listener !=null){

//这里我只传了垂直滑动的距离

listener.onScroll(t);

}

MainActivity - 逻辑

package com.example.thinkpad.demo2.activity;

import android.os.Bundle;

import android.support.annotation.Nullable;

import android.support.v7.app.AppCompatActivity;

import android.view.View;

import android.widget.RelativeLayout;

import android.widget.TextView;

import com.example.thinkpad.demo2.R;

import com.example.thinkpad.demo2.ui.MyScrollView;

public class MainActivityextends AppCompatActivity {

private RelativeLayoutlayoutTitle;

private TextViewtvTitle;

private MyScrollViewscrollView;

@Override

protected void onCreate(@Nullable Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

initView();

}

private void initView() {

scrollView = findViewById(R.id.scrollView);

layoutTitle = findViewById(R.id.rl_title);

tvTitle = findViewById(R.id.tv_title);

//初始化的时候先行隐藏

tvTitle.setVisibility(View.GONE);

layoutTitle.getBackground().setAlpha(0);

//通过上下滑动的距离，动态设置title背景色的透明度与 title的显示状态

scrollView.setOnScrollListener(new MyScrollView.OnScrollListener() {

@Override

public void onScroll(int scrollY) {

if (0 < scrollY && scrollY <=255) {

tvTitle.setVisibility(scrollY >50 ? View.VISIBLE : View.GONE);

layoutTitle.getBackground().setAlpha(scrollY);

}else if (scrollY >255) {

tvTitle.setVisibility(View.VISIBLE);

layoutTitle.getBackground().setAlpha(255);

}else {

tvTitle.setVisibility(View.GONE);

layoutTitle.getBackground().setAlpha(0);

}

});

}