Android ListView滑动改变标题栏背景渐变效果

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <ListView  android:id="@+id/listvew"  android:layout_width="match_parent"  android:layout_height="match_parent"/> <!--标题栏，这里简单写个textview--> <TextView  android:id="@+id/title_tv"  android:layout_width="match_parent"  android:layout_height="wrap_content"  android:background="#00000000"  android:gravity="center"  android:orientation="vertical"  android:padding="5dp"  android:textSize="30sp"/></RelativeLayout>

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:orientation="vertical"> <ImageView  android:id="@+id/head_iv"  android:layout_width="match_parent"  android:layout_height="150dp"  android:background="@mipmap/ch"/></LinearLayout>

<?xml version="1.0" encoding="utf-8"?><FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="50dp"> <TextView  android:id="@+id/item_tv"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:gravity="center"  android:textSize="15sp"> </TextView></FrameLayout>

import android.app.Activity;import android.content.Context;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.AbsListView;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.ListView;import android.widget.TextView;import java.util.ArrayList;public class MainActivity10 extends Activity { private TextView title_tv; private ListView listvew; //listView的头 private View headView; //listView头中包含的布局。这里仅仅是一个ImageView private ImageView head_iv; private ArrayList<String> dataList; private MyAdapter myAdapter; //listview的头部（这里是ImageView）顶部距离屏幕顶部（包含状态栏）的距离 //注：这个高度，是头布局在屏幕里才会计算的，出了屏幕，就不会变了 private int height; //listView的头部的真实高度。头布局的整体高度，因为这个demo只简单写了个ImageView作为头部，所以ImageView的高度，就是头部的高度 private int headViewHeight; private Context context; @Override protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.activity_main_10);  context = this;  title_tv = (TextView) findViewById(R.id.title_tv);  listvew = (ListView) findViewById(R.id.listvew);  headView = LayoutInflater.from(this).inflate(R.layout.head_layout, null);  head_iv = (ImageView) headView.findViewById(R.id.head_iv);  //添加listView的头布局  listvew.addHeaderView(headView);  dataList = new ArrayList<>();  for (int i = 0; i < 50; i++) {   dataList.add("==" + i + "==");  }  myAdapter = new MyAdapter();  listvew.setAdapter(myAdapter);  listvew.setOnScrollListener(new AbsListView.OnScrollListener() {   @Override   public void onScrollStateChanged(AbsListView view, int scrollState) {   }   @Override   public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {    int location[] = new int[2];    /**     * public void getLocationInWindow(@Size(2) int[] location)     *     * <p>Computes 计算 the coordinates 坐标 of this view in its window. The argument 参数     * must be an array of two integers. After the method returns, the array     * contains 包含 the x and y location in that order.</p>     *     * @param location an array of two integers in which to hold the coordinates     */    head_iv.getLocationInWindow(location);    //listview的头部（这里是ImageView）顶部距离屏幕顶部（包含状态栏）的距离    height = location[1];    headViewHeight = head_iv.getHeight();    Utils.printLogData("==location==0==" + location[0]);    Utils.printLogData("==location==1==" + location[1]);    Utils.printLogData("==height==" + height);    Utils.printLogData("==headViewHeight==" + headViewHeight);    //在head_layout.xml中，固定设置了150dp的高度，用于和上面测量的对比    Utils.printLogData("==setHeigth==" + dip2px(150));    handleTitleBarColorEvaluate();   }  }); } // 处理标题栏颜色渐变 private void handleTitleBarColorEvaluate() {  //比例  float fraction;  if (height > 0) {   fraction = 1f - height * 1f / 60;   if (fraction < 0f) {    fraction = 0f;   }   title_tv.setAlpha(fraction);   return;  }  //高度值是负数，但是负号仅仅是表示方向，取绝对值  float space = Math.abs(height) * 1f;  // 标题栏的高度  fraction = space / headViewHeight;  if (fraction < 0f)   fraction = 0f;  if (fraction > 1f)   fraction = 1f;  title_tv.setAlpha(1f);  if (fraction >= 1f) {   title_tv.setBackgroundColor(0xffec434b);  } else {   //根据比例，生成一个按比例的颜色值   title_tv.setBackgroundColor(ChenColorUtils.getNewColorByStartEndColor(context, fraction, R.color.transparent, R.color.red));  }  if (fraction >= 0.8f) {   title_tv.setTextColor(ChenColorUtils.getNewColorByStartEndColor(context, fraction, R.color.transparent, R.color.black));   title_tv.setText("标题栏");  } else {   title_tv.setText("");  } } private class MyAdapter extends BaseAdapter {  @Override  public int getCount() {   return dataList.size();  }  @Override  public Object getItem(int position) {   return null;  }  @Override  public long getItemId(int position) {   return 0;  }  @Override  public View getView(int position, View convertView, ViewGroup parent) {   ViewHolder holder;   if (convertView == null) {    convertView = LayoutInflater.from(context).inflate(R.layout.listview_item_layout, null);    holder = new ViewHolder();    holder.item_tv = (TextView) convertView.findViewById(R.id.item_tv);    convertView.setTag(holder);   } else {    holder = (ViewHolder) convertView.getTag();   }   holder.item_tv.setText(dataList.get(position));   return convertView;  }  private class ViewHolder {   private TextView item_tv;  } } /**  * dip转换px  */ public int dip2px(int dip) {  final float scale = context.getResources().getDisplayMetrics().density;  return (int) (dip * scale + 0.5f); }}

<color name="red">#ec434b</color><color name="transparent">#00000000</color><color name="black">#FF000000</color>

import android.util.Log;public class Utils { public static void printLogData(String data) {  Log.e("chen", data); }}

import android.content.Context;public class ChenColorUtils { // 成新的颜色值 public static int getNewColorByStartEndColor(Context context, float fraction, int startValue, int endValue) {  return evaluate(fraction, context.getResources().getColor(startValue), context.getResources().getColor(endValue)); } /**  * 成新的颜色值  * @param fraction 颜色取值的级别 (0.0f ~ 1.0f)  * @param startValue 开始显示的颜色  * @param endValue 结束显示的颜色  * @return 返回生成新的颜色值  */ public static int evaluate(float fraction, int startValue, int endValue) {  int startA = (startValue >> 24) & 0xff;  int startR = (startValue >> 16) & 0xff;  int startG = (startValue >> 8) & 0xff;  int startB = startValue & 0xff;  int endA = (endValue >> 24) & 0xff;  int endR = (endValue >> 16) & 0xff;  int endG = (endValue >> 8) & 0xff;  int endB = endValue & 0xff;  return ((startA + (int) (fraction * (endA - startA))) << 24) |    ((startR + (int) (fraction * (endR - startR))) << 16) |    ((startG + (int) (fraction * (endG - startG))) << 8) |    ((startB + (int) (fraction * (endB - startB)))); }}