用戶要求一個特效，做了一個Demo，分享一下。

1.羅列代碼

• ListView headView布局文件

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><View android:id="@+id/placeholder_top"android:layout_width="match_parent"android:layout_height="200dp"android:background="@android:color/transparent" /><View android:id="@+id/placeholder_sticky"android:layout_width="match_parent"android:layout_height="50dp" /> </LinearLayout>

• 主布局文件

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent" ><View android:id="@+id/top"android:layout_width="match_parent"android:layout_height="200dp"android:background="@drawable/ic_launcher" /><ListView android:id="@+id/listView"android:layout_width="match_parent"android:layout_height="wrap_content" ></ListView><TextView android:id="@+id/sticky"android:layout_width="match_parent"android:layout_height="50dp"android:background="#00ffff"android:gravity="center"android:textColor="#ff0000"android:text="Sticky"android:textSize="20sp" /> </FrameLayout>

• 主代碼

package com.example.android.listviewscrolltrick;import java.util.ArrayList; import java.util.List;import android.annotation.SuppressLint; import android.app.Activity; import android.content.Context; import android.os.Build; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewTreeObserver; import android.view.Window; import android.widget.AbsListView; import android.widget.ArrayAdapter; import android.widget.ListView; import android.widget.TextView;import com.example.listviewscrolltrick.R;public class MainActivity extends Activity {private TextView mStickyView;private View mPlaceHolderSticky;private ListView mListView;private View mTopView;@SuppressWarnings("deprecation")@Overrideprotected void onCreate(Bundle savedInstanceState) {requestWindowFeature(Window.FEATURE_NO_TITLE);super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mStickyView = (TextView) findViewById(R.id.sticky);mListView = (ListView) findViewById(R.id.listView);mTopView = findViewById(R.id.top);LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);View headView = inflater.inflate(R.layout.layout_headview, null);mPlaceHolderSticky = headView.findViewById(R.id.placeholder_sticky);mListView.addHeaderView(headView);mListView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {@SuppressLint("NewApi")@SuppressWarnings("deprecation")@Overridepublic void onGlobalLayout() {onScrollChanged();ViewTreeObserver obs = mListView.getViewTreeObserver();if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {obs.removeOnGlobalLayoutListener(this);} else {obs.removeGlobalOnLayoutListener(this);}}});mListView.setOnScrollListener(new AbsListView.OnScrollListener() {@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {}@Overridepublic void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {onScrollChanged();}});List<String> dataSource = new ArrayList<String>();for (int j = 0; j < 20; j++) {dataSource.add("item-----" + j);}ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, dataSource);mListView.setAdapter(arrayAdapter);}private void onScrollChanged() {View v = mListView.getChildAt(0);int top = (v == null) ? 0 : v.getTop();if (mListView.getFirstVisiblePosition() == 0) {mStickyView.setTranslationY(Math.max(mPlaceHolderSticky.getTop()+ top, 0));mTopView.setTranslationY(top);}} }

2.大致原理講解

• ListView headView存在兩塊區域：R.id.placeholder_top /R.id.placeholder_sticky
  這兩者是“地下工作者”，他們分別與mTopView/mStickView對應——高度相同，顏色透明

• ListView加載完成后，調整mTopView/mStickView組件的位置

• ListView滑動時，調整mTopView&&mStickyView的位置

3.結合源代碼對原理進行深入講解

• 初始階段位置的調整
  對ListView加載完成進行監聽
  注意：要取消監聽

mListView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {@SuppressLint("NewApi")@SuppressWarnings("deprecation")@Overridepublic void onGlobalLayout() {onScrollChanged();ViewTreeObserver obs = mListView.getViewTreeObserver();if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {obs.removeOnGlobalLayoutListener(this);} else {obs.removeGlobalOnLayoutListener(this);}}});

• 根據ListView中headView中的對應部分 ，設置mTopView/mStickView位置

private void onScrollChanged() {View v = mListView.getChildAt(0);int top = (v == null) ? 0 : v.getTop();if (mListView.getFirstVisiblePosition() == 0) {mStickyView.setTranslationY(Math.max(mPlaceHolderSticky.getTop()+ top, 0));mTopView.setTranslationY(top);}}

由于mStickyView要一直顯示在可見范圍內，所以mStickyView.setTranslationY一定不能為負數.

• ListView滑動

監聽ListView滑動，調整mTopView/mStickView的位置（同上）

mListView.setOnScrollListener(new AbsListView.OnScrollListener() {@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {}@Overridepublic void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {onScrollChanged();}});

3.Demo下載

http://download.csdn.net/detail/guchuanhang/9515429

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