在项目中，我们常常需要实现界面滑动切换的效果。例如，微信界面的左右滑动切换效果。那这种效果是怎么实现的？今天我就带大家简单了解ViewPager，并通过实例来实现该效果。
一. ViewPager 官方API
首先我们来看一下ViewPager官方给出的解释，如图：
具体意思如下：
Layout 管理器允许用户可以在页面上，左右滑动来翻动页面。你可以考虑实现PagerAdapter接口来显示该效果。
ViewPager很多时候会结合Fragment一块使用，这种方法使得管理每个页面的生命周期变得很方便。其中，有一些adapter的具体实现，可以适合于这种ViewPager结合Fragment使用的情况。这些adapter包括：FragmentPagerAdapter,和 FragmentStatePagerAdapter。
而本文就是通过ViewPager结合Fragment利用FragmentpagerAdapter适配器来实现左右滑动的效果。
二.效果如下：
三.代码实现：
1.xml布局文件
1>主布局activity_main.xml
<span style="font-family:Microsoft YaHei;font-size:18px;"><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<include layout="@layout/activity_main_top_tab" />
<android.support.v4.view.ViewPager
android:id="@+id/id_page_vp"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" >
</android.support.v4.view.ViewPager>
</LinearLayout></span>注意：布局中加载android.support.v4.view.ViewPager,所有需要引入android-support-v4.jar(正常情况系统会自动引入)
2>顶部导航activity_main_top_tab.xml
<span style="font-family:Microsoft YaHei;font-size:18px;"><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<LinearLayout
android:id="@+id/id_switch_tab_ll"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:baselineAligned="false"
>
<LinearLayout
android:id="@+id/id_tab_chat_ll"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:background="@drawable/guide_round_selector"
android:gravity="center"
android:orientation="horizontal"
android:padding="10dip" >
<TextView
android:id="@+id/id_chat_tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="聊天"
android:textColor="#0000FF"
android:textSize="15dip" />
</LinearLayout>
<LinearLayout
android:id="@+id/id_tab_friend_ll"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:background="@drawable/guide_round_selector"
android:clickable="true"
android:gravity="center"
android:orientation="horizontal"
android:padding="10dip"
android:saveEnabled="false" >
<TextView
android:id="@+id/id_friend_tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="好友"
android:textColor="#000000"
android:textSize="15dip" />
</LinearLayout>
<LinearLayout
android:id="@+id/id_tab_contacts_ll"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:background="@drawable/guide_round_selector"
android:focusable="false"
android:gravity="center"
android:orientation="horizontal"
android:padding="10dip" >
<TextView
android:id="@+id/id_contacts_tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="通讯录"
android:textColor="#000000"
android:textSize="15dip" />
</LinearLayout>
</LinearLayout>
<ImageView
android:id="@+id/id_tab_line_iv"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:contentDescription="tab"
android:background="@drawable/tab_selected_pressed_holo" >
</ImageView>
<View
android:layout_width="match_parent"
android:layout_height="1dp"
android:background="#000000" />
</LinearLayout></span><span style="font-family:Microsoft YaHei;font-size:18px;"><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="聊天界面"
android:textColor="#FF0000"
android:textSize="20sp"
android:gravity="center"
></TextView>
</LinearLayout></span>4>主函数MainActivity.java
<span style="font-family:Microsoft YaHei;font-size:18px;">package com.example.viewpagerdemo;
import java.util.ArrayList;
import java.util.List;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.DisplayMetrics;
import android.util.Log;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
public class MainActivity extends FragmentActivity {
private List<Fragment> mFragmentList = new ArrayList<Fragment>();
private FragmentAdapter mFragmentAdapter;
private ViewPager mPageVp;
/**
* Tab显示内容TextView
*/
private TextView mTabChatTv, mTabContactsTv, mTabFriendTv;
/**
* Tab的那个引导线
*/
private ImageView mTabLineIv;
/**
* Fragment
*/
private ChatFragment mChatFg;
private FriendFragment mFriendFg;
private ContactsFragment mContactsFg;
/**
* ViewPager的当前选中页
*/
private int currentIndex;
/**
* 屏幕的宽度
*/
private int screenWidth;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findById();
init();
initTabLineWidth();
}
private void findById() {
mTabContactsTv = (TextView) this.findViewById(R.id.id_contacts_tv);
mTabChatTv = (TextView) this.findViewById(R.id.id_chat_tv);
mTabFriendTv = (TextView) this.findViewById(R.id.id_friend_tv);
mTabLineIv = (ImageView) this.findViewById(R.id.id_tab_line_iv);
mPageVp = (ViewPager) this.findViewById(R.id.id_page_vp);
}
private void init() {
mFriendFg = new FriendFragment();
mContactsFg = new ContactsFragment();
mChatFg = new ChatFragment();
mFragmentList.add(mChatFg);
mFragmentList.add(mFriendFg);
mFragmentList.add(mContactsFg);
mFragmentAdapter = new FragmentAdapter(
this.getSupportFragmentManager(), mFragmentList);
mPageVp.setAdapter(mFragmentAdapter);
mPageVp.setCurrentItem(0);
mPageVp.setOnPageChangeListener(new OnPageChangeListener() {
/**
* state滑动中的状态 有三种状态（0，1，2） 1：正在滑动 2：滑动完毕 0：什么都没做。
*/
@Override
public void onPageScrollStateChanged(int state) {
}
/**
* position :当前页面，及你点击滑动的页面 offset:当前页面偏移的百分比
* offsetPixels:当前页面偏移的像素位置
*/
@Override
public void onPageScrolled(int position, float offset,
int offsetPixels) {
LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) mTabLineIv
.getLayoutParams();
Log.e("offset:", offset + "");
/**
* 利用currentIndex(当前所在页面)和position(下一个页面)以及offset来
* 设置mTabLineIv的左边距 滑动场景：
* 记3个页面,
* 从左到右分别为0,1,2
* 0->1; 1->2; 2->1; 1->0
*/
if (currentIndex == 0 && position == 0)// 0->1
{
lp.leftMargin = (int) (offset * (screenWidth * 1.0 / 3) + currentIndex
* (screenWidth / 3));
} else if (currentIndex == 1 && position == 0) // 1->0
{
lp.leftMargin = (int) (-(1 - offset)
* (screenWidth * 1.0 / 3) + currentIndex
* (screenWidth / 3));
} else if (currentIndex == 1 && position == 1) // 1->2
{
lp.leftMargin = (int) (offset * (screenWidth * 1.0 / 3) + currentIndex
* (screenWidth / 3));
} else if (currentIndex == 2 && position == 1) // 2->1
{
lp.leftMargin = (int) (-(1 - offset)
* (screenWidth * 1.0 / 3) + currentIndex
* (screenWidth / 3));
}
mTabLineIv.setLayoutParams(lp);
}
@Override
public void onPageSelected(int position) {
resetTextView();
switch (position) {
case 0:
mTabChatTv.setTextColor(Color.BLUE);
break;
case 1:
mTabFriendTv.setTextColor(Color.BLUE);
break;
case 2:
mTabContactsTv.setTextColor(Color.BLUE);
break;
}
currentIndex = position;
}
});
}
/**
* 设置滑动条的宽度为屏幕的1/3(根据Tab的个数而定)
*/
private void initTabLineWidth() {
DisplayMetrics dpMetrics = new DisplayMetrics();
getWindow().getWindowManager().getDefaultDisplay()
.getMetrics(dpMetrics);
screenWidth = dpMetrics.widthPixels;
LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) mTabLineIv
.getLayoutParams();
lp.width = screenWidth / 3;
mTabLineIv.setLayoutParams(lp);
}
/**
* 重置颜色
*/
private void resetTextView() {
mTabChatTv.setTextColor(Color.BLACK);
mTabFriendTv.setTextColor(Color.BLACK);
mTabContactsTv.setTextColor(Color.BLACK);
}
}
</span>
注意：
1.MainActivity继承于FragmentActivity;
2.初始化导航条的宽度：initTabLineWidth()，由于本例给出的是3个界面切换，固长度为整个屏幕宽度的1/3;
3.监听事件OnPageChangeListener的onPageScrolled方法主要捕捉滑动事件;
其中给出了3个参数所表示的意义。根据滑动的4中变化(左-中-右-中-左)，给出导航条距离左边的边距，显示导航条滑动的效果。
<span style="font-family:Microsoft YaHei;font-size:18px;">package com.example.viewpagerdemo;
import java.util.ArrayList;
import java.util.List;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
public class FragmentAdapter extends FragmentPagerAdapter {
List<Fragment> fragmentList = new ArrayList<Fragment>();
public FragmentAdapter(FragmentManager fm,List<Fragment> fragmentList) {
super(fm);
this.fragmentList = fragmentList;
}
@Override
public Fragment getItem(int position) {
return fragmentList.get(position);
}
@Override
public int getCount() {
return fragmentList.size();
}
}
</span><span style="font-family:Microsoft YaHei;font-size:18px;">package com.example.viewpagerdemo;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class ChatFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState){
super.onCreateView(inflater, container, savedInstanceState);
View chatView = inflater.inflate(R.layout.activity_tab_chat, container,false);
return chatView;
}
@Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
}
}
</span>上面就是本文的所有内容。
源码下载地址：http://download.csdn.net/detail/a123demi/7943901
Android ViewPager和Fragment实现顶部导航界面滑动效果
原文：http://blog.csdn.net/a123demi/article/details/39480385