【Android】ViewPager探索

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在layout.xml中只放一个ViewPager

<?xml version="1.0" encoding="utf-8"?><LinearLayout    android:orientation="vertical"    >    <android.support.v4.view.ViewPager        android:layout_width="match_parent"        android:layout_height="0dp"        android:layout_weight="1"        android:id="@+id/id_view_pager"/></LinearLayout>

尽量不要复制，手打好一点，快一点
onCreate中总共做了三件事，初始化View，初始化适配器和初始化ViewPager

Activity extends FragmentActivity {    private ViewPager mViewPager;    private List<Fragment> mListFragment;    private FragmentPagerAdapter mFragmentPagerAdapter;    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.layout);        initView();        initAdapter();        initViewPager();    }}

其中初始化View，初始化适配器函数如下，适配器特别简单，只需要两个返回函数。Ctrl键+F关注mListFragment的操作

Activity extends FragmentActivity {    private void initView(){        mViewPager =findViewById(R.id.id_view_pager);    }    private void initAdapter(){        mListFragment=new ArrayList<>();        mListFragment.add(new FirstFragment());        mListFragment.add(new SecondFragment());        //getSupportFragmentManager方法来自FragmentActivity        mFragmentPagerAdapter=new FragmentPagerAdapter(getSupportFragmentManager()) {            @Override            public Fragment getItem(int position) {                return mListFragment.get(position);            }            @Override            public int getCount() {                return mListFragment.size();            }        };    }}

其中的FirstFragment.java如下
可以把onCreateView当成活动的onCreate，inflate当成setContentView，只不过inflate是加载，setContentView是显示。

public class FirstFragment extends Fragment{    @Nullable    @Override    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {        return inflater.inflate(R.layout.first_layout,container,false);    }}

first_layout.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout    xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="match_parent">    <ImageView        android:layout_width="match_parent"        android:layout_height="match_parent"        android:src="@drawable/dreamcatcher"/></LinearLayout>

很简单，就一张图

第二个SecondFragment.java如下

public class SecondFragment extends Fragment{    @Nullable    @Override    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {        return inflater.inflate(R.layout.second_layout,container,false);    }}

second_layout.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical" android:layout_width="match_parent"    android:layout_height="match_parent">    <ImageView        android:layout_width="match_parent"        android:layout_height="match_parent"        android:src="@drawable/axes"/></LinearLayout>

两个Fragment是为了做List< Fragment >，而做List< Fragment >是为了给FragmentPagerAdapter配逻辑，能通过mListFragment找到相关的Fragment显示出来。

最后一个函数初始化viewpager，设置了适配器以后就可以选择显示哪一项了

Activity extends FragmentActivity {    private void initViewPager(){        mViewPager.setAdapter(mFragmentPagerAdapter);        mViewPager.setCurrentItem(0);        mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {            @Override            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {            }            @Override            public void onPageSelected(int position) {                mViewPager.setCurrentItem(position);                //一般在此选择改变按钮的颜色            }            @Override            public void onPageScrollStateChanged(int state) {            }        });    }}

一般我们为了做出滑动时按键同时变色的效果，可以用一个函数设置所有的按钮变为未选中状态，然后设定相关的按钮为选中状态，（起setButtonImageToSelectAndSelectItem这个长名是为了好辨认）

Activity extends FragmentActivity {    //三个Tab对应的Button    private Button mTabLeftButton;    private Button mTabCenterButton;    private Button mTabRightButton;    private void setButtonImageToSelectAndSelectItem(int i){        //设置全部为默认        mTabCenterButton.setBackgroundResource(R.drawable.center_normal_img);        mTabCenterButton.setTextColor(Color.parseColor("#000000"));        mTabLeftButton.setBackgroundResource(R.drawable.left_normal_img);        mTabLeftButton.setTextColor(Color.parseColor("#000000"));        mTabRightButton.setBackgroundResource(R.drawable.right_normal_img);        mTabRightButton.setTextColor(Color.parseColor("#000000"));        //根据传入参数选则选中按钮        switch (i){            case 0:                mTabLeftButton.setBackgroundResource(R.drawable.left_selected_img);                mTabLeftButton.setTextColor(Color.parseColor("#ffffff"));                break;            case 1:                mTabCenterButton.setBackgroundResource(R.drawable.center_selected_img);                mTabCenterButton.setTextColor(Color.parseColor("#ffffff"));                break;            case 2:                mTabRightButton.setBackgroundResource(R.drawable.right_selected_img);                mTabRightButton.setTextColor(Color.parseColor("#ffffff"));        }        mViewPager.setCurrentItem(i);    }}

然后在点击事件和页面选中事件中设置它

    @Override    public void onClick(View view) {        switch (view.getId()){            case R.id.id_left_button:                setButtonImageToSelectAndSelectItem(0);                break;            case R.id.id_center_button:                setButtonImageToSelectAndSelectItem(1);                break;            case R.id.id_right_button:                setButtonImageToSelectAndSelectItem(2);                break;        }    }    private void initEvents(){        mTabCenterButton.setOnClickListener(this);        mTabLeftButton.setOnClickListener(this);        mTabRightButton.setOnClickListener(this);        mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {            @Override            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {            }            @Override            public void onPageSelected(int position) {                setButtonImageToSelectAndSelectItem(position);            }            @Override            public void onPageScrollStateChanged(int state) {            }        });    }

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