仿qq底部Tab导航

柔光的暖阳◎ 2022-07-16 10:49 185阅读 0赞

## 本篇博客主要实现以下效果： ##

*  使用FragmentTabHost实现qq底部Tab切换
 *  使用RadioGroup和RadioButton实现仿qq底部切换
 *  使用RadioGroup和ViewPager 实现可以滑动切换的仿qq底部Tab切换
 *  解决Fragment多次实例化的几种方案
 *  Fragemnt的懒加载（网上很多人称之为Fragemnt的最优加载）

## 效果图 ##

老规矩，废话 不多说，先看效果图

### FragmentTabHost实现qq底部Tab实践的效果图 ###

![9fe4afa0jw1f8szzo4g0rg209c0gdq4i.gif][]

### RadioGroup和ViewPager 实现可以滑动切换的仿qq底部Tab效果图 ###

![9fe4afa0gw1f8t00ub0hng208l0ekabn.gif][]

## 使用FragmentTabHost实现qq底部Tab切换 ##

### 第一步先看布局文件 ###

<?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="match_parent"
                  android:orientation="vertical">
        
        <FrameLayout
            android:id="@+id/main_layout_content"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1">
        </FrameLayout>
        
        <android.support.v4.app.FragmentTabHost
            android:id="@android:id/tabhost"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="#F6F6F6"
            android:paddingBottom="5dp"
            android:paddingTop="5dp">
    
            <FrameLayout
                android:id="@android:id/tabcontent"
                android:layout_width="0dp"
                android:layout_height="0dp"/>
        </android.support.v4.app.FragmentTabHost>
    
    </LinearLayout>

其实很简单，没什么好说的 ，就是一个vertical的LinearLayout中放置着一个FrameLayout和FragmentTabHost

### 接下来我们来看一下代码 ###

public class FirstStyleActivity extends AppCompatActivity { 
        FragmentTabHost mTabHost;
        private TabWidget mTabWidget;
        private List<FragmentInfo> mFragmentEntities;
        private static final String TAG = "xujun";
        private static final String tag = "tag";
        public static final String[] mTiltles = new String[]{
                "首页", "课程", "直播", "个人"
        };
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_first_style);
            mTabHost = (FragmentTabHost) findViewById(android.R.id.tabhost);
    
            mTabHost.setup(this, getSupportFragmentManager(), R.id.main_layout_content);
            mTabWidget = mTabHost.getTabWidget();
            // 去掉分割线
            mTabWidget.setDividerDrawable(null);
            mFragmentEntities = MainFragmentFactory.getInstance().getList();
            initListener();
            initData();
    
    
        }
    
        private void initData() {
            int size = mFragmentEntities.size();
            for (int i = 0; i < size; i++) {
                Log.i(TAG, "size:=" + size);
                FragmentInfo fragmentInfo = mFragmentEntities.get(i);
                String title = fragmentInfo.getTitle();
                TabHost.TabSpec tabSpec = mTabHost.newTabSpec(title).setIndicator(getTabView
                        (i));
                Bundle bundle = new Bundle();
                bundle.putString(tag, mTiltles[i]);
    
                mTabHost.addTab(tabSpec, fragmentInfo.getClz(), bundle);
            }
            updateTab(0);
        }
    
        private void initListener() {
            mTabHost.setOnTabChangedListener(new TabHost.OnTabChangeListener() {
                @Override
                public void onTabChanged(String tabId) {
                    int currentTab = mTabHost.getCurrentTab();
                    Log.i(TAG, "onTabChanged：currentTab:=" + currentTab);
                    updateTab(currentTab);
                }
            });
        }
    
        private View getTabView(int i) {
            View view = View.inflate(this, R.layout.tab_layout, null);
            int currentTab = mTabHost.getCurrentTab();
            Log.i(TAG, "currentTab:=" + currentTab);
            setSingleView(view, currentTab, i);
            return view;
        }
    
        private void setSingleView(View view, int currentTab, int index) {
            FragmentInfo fragmentInfo = mFragmentEntities.get(index);
            int[] imagIds = fragmentInfo.getImagIds();
            int[] colors = fragmentInfo.getColors();
            TextView tv = (TextView) view.findViewById(R.id.tab_tv);
            ImageView iv = (ImageView) view.findViewById(R.id.tab_icon);
            tv.setText(fragmentInfo.getTitle());
            Resources resources = getResources();
            if (index == currentTab) {
    
                tv.setTextColor(resources.getColor(colors[1]));
                iv.setImageDrawable(resources.getDrawable(imagIds[1]));
            } else {
                tv.setTextColor(getResources().getColor(colors[0]));
                iv.setImageDrawable(resources.getDrawable(imagIds[0]));
            }
        }
    
        private void updateTab(int currentTab) {
    
            int childCount = mTabWidget.getChildCount();
            for (int i = 0; i < childCount; i++) {
                View view = mTabWidget.getChildTabViewAt(i);
                setSingleView(view, currentTab, i);
    
            }
    
    
        }
    }

其实说起来也很简单，主要分为以下步骤

*  第一步，实例化FragmentTabHost并设置相关样式

mTabHost = (FragmentTabHost) findViewById(android.R.id.tabhost);
    
    mTabHost.setup(this, getSupportFragmentManager(), R.id.main_layout_content);
    mTabWidget = mTabHost.getTabWidget();
    // 去掉分割线
    mTabWidget.setDividerDrawable(null);

*  第二步,添加每一个TabHost

for (int i = 0; i < size; i++) {
        Log.i(TAG, "size:=" + size);
        FragmentInfo fragmentInfo = mFragmentEntities.get(i);
        String title = fragmentInfo.getTitle();
        TabHost.TabSpec tabSpec = mTabHost.newTabSpec(title).setIndicator(getTabView
                (i));
        Bundle bundle = new Bundle();
        bundle.putString(tag, mTiltles[i]);
    
        mTabHost.addTab(tabSpec, fragmentInfo.getClz(), bundle);
    }

*  第三步，通过设置 监听器来实现底部tab颜色和图案样式的转换

mTabHost.setOnTabChangedListener(new TabHost.OnTabChangeListener() {
        @Override
        public void onTabChanged(String tabId) {
            int currentTab = mTabHost.getCurrentTab();
            Log.i(TAG, "onTabChanged：currentTab:=" + currentTab);
            updateTab(currentTab);
        }
    });

### 运行上述代码及可以看到如下效果图 ###

![9fe4afa0jw1f8szzo4g0rg209c0gdq4i.gif][]

--------------------

## 使用RadioGroup和RadioButton实现仿qq底部切换 ##

### 第一步 ，先看布局文件 ###

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout
        android:id="@+id/activity_second_style"
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
    >
        
        <FrameLayout
            android:id="@+id/fl"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1">
    
        </FrameLayout>
        
        <RadioGroup
    
            android:id="@+id/rg"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
        >
            <RadioButton
                android:id="@+id/rb_home"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_home"
                android:text="首页"/>
    
            <RadioButton
                android:id="@+id/rb_course"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_course"
                android:text="课程"/>
    
            <RadioButton
                android:id="@+id/rb_direct_seeding"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_direct_seeding"
                android:text="直播"/>
    
            <RadioButton
                android:id="@+id/rb_me"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_me"
                android:text="我的"/>
    
        </RadioGroup>
    
    </LinearLayout>

其实每一个tab的选中时利用RadioGroup中RadioButton的互相排斥的特性，即每一次只能选中一个 RadioButton

至于bottom\_tab的style，只不过是将相同的arr提取出来，减少布局的代码量和方便统一修改而已，平时我们在写布局代码 的时候也可以这样

### 第二步，我们来看一下Activity的 代码 ###

public class ThreeActivity extends AppCompatActivity { 
    
        FrameLayout mFl;
        RadioGroup mRg;
        private FragmentManager mFragmentManager;
    
        private int position = 0;
    
        public static final String[] mTiltles = new String[]{
                "首页", "课程", "直播", "个人"
        };
        private List<Fragment> mFragments;
        private Fragment mCurFragment;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_three);
            mFl = (FrameLayout) findViewById(R.id.fl);
            mRg = (RadioGroup) findViewById(R.id.rg);
            mFragments = new ArrayList<>();
            for (int i = 0; i < mTiltles.length; i++) {
                ItemFragement itemFragement = ItemFragement.newInstance(mTiltles[i]);
                mFragments.add(itemFragement);
            }
            mCurFragment = mFragments.get(position);
            replaceFragment(mCurFragment);
    
            ((RadioButton)mRg.getChildAt(position)).setChecked(true);
    
            initListener();
        }
    
        private void initListener() {
            mRg.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
    
                @Override
                public void onCheckedChanged(RadioGroup group, int checkedId) {
    
                    RadioButton radioButton = (RadioButton) group.findViewById(checkedId);
    
                    if (false == radioButton.isChecked()) {
                        return;
                    }
    
    
                    switch (checkedId) {
                        case R.id.rb_home:
                            position = 0;
                            break;
    
                        case R.id.rb_course:
                            position = 1;
                            break;
    
                        case R.id.rb_direct_seeding:
                            position = 2;
                            break;
    
                        case R.id.rb_me:
                            position = 3;
                            break;
                        default:
                            position = 0;
                            break;
    
                    }
                    LUtils.i("position==" + position);
    
                    Fragment to = mFragments.get(position);
                    showFragment(mCurFragment, to);
                    mCurFragment = to;
    
                }
    
            });
        }
    
        private void showFragment(Fragment from, Fragment to) {
            FragmentManager supportFragmentManager = getSupportFragmentManager();
            FragmentTransaction transaction = supportFragmentManager.beginTransaction();
            if (!to.isAdded()) {    // 先判断是否被add过
                transaction.hide(from).add(R.id.fl, to).commit(); // 隐藏当前的fragment，add下一个到Activity中
            } else {
                transaction.hide(from).show(to).commit(); // 隐藏当前的fragment，显示下一个
            }
    
        }
    
        /** * 这个方法用老替换fragment * xujun * 2016/5/3 17:28. */
    
        private void replaceFragment(Fragment fragmeny) {
            FragmentManager supportFragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = supportFragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.fl, fragmeny).commit();
        }
    
    }

思路解析

*  实例化各个控件，这里代码就不贴出来了
 *  初始化 Fragemnt 和选中各个tab

mFragments = new ArrayList<>();
    for (int i = 0; i < mTiltles.length; i++) {
        ItemFragement itemFragement = ItemFragement.newInstance(mTiltles[i]);
        mFragments.add(itemFragement);
    }
    mCurFragment = mFragments.get(position);
    replaceFragment(mCurFragment);
    
    ((RadioButton)mRg.getChildAt(position)).setChecked(true);
    
    private void replaceFragment(Fragment fragmeny) {
        FragmentManager supportFragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = supportFragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.fl, fragmeny).commit();
    }

*  第三步，通过监听RadioGroup的 OnCheckedChangeListener事件，来实现tab和Fragemnt的切换

mRg.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
    
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
    
            RadioButton radioButton = (RadioButton) group.findViewById(checkedId);
    
            if (false == radioButton.isChecked()) {
                return;
            }
    
    
            switch (checkedId) {
                case R.id.rb_home:
                    position = 0;
                    break;
    
                case R.id.rb_course:
                    position = 1;
                    break;
    
                case R.id.rb_direct_seeding:
                    position = 2;
                    break;
    
                case R.id.rb_me:
                    position = 3;
                    break;
                default:
                    position = 0;
                    break;
    
            }
            LUtils.i("position==" + position);
    
            Fragment to = mFragments.get(position);
            showFragment(mCurFragment, to);
            mCurFragment = to;
    
        }
    
    });

--------------------

## 使用RadioGroup和ViewPager 实现可以滑动切换的仿qq底部Tab切换 ##

### 第一步，我们 同样先看布局代码 ###

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout
        android:id="@+id/activity_second_style"
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
    >
        
        <android.support.v4.view.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1">
    
        </android.support.v4.view.ViewPager>
        
        <RadioGroup
    
            android:id="@+id/rg"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
        >
            <RadioButton
                android:id="@+id/rb_home"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_home"
                android:text="首页"/>
    
            <RadioButton
                android:id="@+id/rb_course"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_course"
                android:text="课程"/>
    
            <RadioButton
                android:id="@+id/rb_direct_seeding"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_direct_seeding"
                android:text="直播"/>
    
            <RadioButton
                android:id="@+id/rb_me"
                style="@style/bottom_tab"
                android:drawableTop="@drawable/sel_me"
                android:text="我的"/>
    
        </RadioGroup>
    
    </LinearLayout>

### 第二步，我们一起来看一下Activity代码 ###

public class SecondStyleActivity extends AppCompatActivity { 
    
        public static final String[] mTiltles = new String[]{
                "首页", "课程", "直播", "个人"
        };
        private List<Fragment> mFragments;
        ViewPager mViewPager;
        RadioGroup mRg;
        private int position = 0;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_second_style);
            mViewPager = (ViewPager) findViewById(R.id.viewPager);
            mRg = (RadioGroup) findViewById(R.id.rg);
            initListener();
            initData();
    
    
        }
    
        private void initData() {
            mFragments = new ArrayList<>();
            for (int i = 0; i < mTiltles.length; i++) {
                ItemFragement itemFragement = ItemFragement.newInstance(mTiltles[i]);
                mFragments.add(itemFragement);
            }
            BaseFragmentAdapter fragmentAdapter = new BaseFragmentAdapter
                    (getSupportFragmentManager(), mFragments, mTiltles);
            mViewPager.setAdapter(fragmentAdapter);
            mViewPager.setCurrentItem(position);
            ((RadioButton) mRg.getChildAt(position)).setChecked(true);
        }
    
        private void initListener() {
            mViewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
                @Override
                public void onPageSelected(int position) {
                    RadioButton radioButton = (RadioButton) mRg.getChildAt(position);
                    radioButton.setChecked(true);
                }
            });
    
            mRg.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
    
                @Override
                public void onCheckedChanged(RadioGroup group, int checkedId) {
                    RadioButton rb = (RadioButton) group.findViewById(checkedId);
                    if (!rb.isChecked()) {
                        return;
                    }
                    switch (checkedId) {
                        case R.id.rb_home:
                            position = 0;
                            break;
    
                        case R.id.rb_course:
                            position = 1;
                            break;
    
                        case R.id.rb_direct_seeding:
                            position = 2;
                            break;
    
                        case R.id.rb_me:
                            position = 3;
                            break;
                        default:
                            position = 0;
                            break;
    
                    }
                    mViewPager.setCurrentItem(position);
                }
            });
        }
    }

*思路解析如下*

*  实例化ViewPager和RadioGroup

mViewPager = (ViewPager) findViewById(R.id.viewPager);
     mRg = (RadioGroup) findViewById(R.id.rg);

*  第二步，初始化ViewPager的适配器和选中 那个tab

mFragments = new ArrayList<>();
    for (int i = 0; i < mTiltles.length; i++) {
        ItemFragement itemFragement = ItemFragement.newInstance(mTiltles[i]);
        mFragments.add(itemFragement);
    }
    BaseFragmentAdapter fragmentAdapter = new BaseFragmentAdapter
            (getSupportFragmentManager(), mFragments, mTiltles);
    mViewPager.setAdapter(fragmentAdapter);
    mViewPager.setCurrentItem(position);
    ((RadioButton) mRg.getChildAt(position)).setChecked(true);

*  第三步，监听ViewPager 的滑动事件和RadioGroup的OnCheckedChangeListener事件，分别切换到相应的 Fragemnt 和同步ViewPager中 position 与RadioGroup之间的联系

mViewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            RadioButton radioButton = (RadioButton) mRg.getChildAt(position);
            radioButton.setChecked(true);
        }
    });
    
    mRg.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
    
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
            RadioButton rb = (RadioButton) group.findViewById(checkedId);
            if (!rb.isChecked()) {
                return;
            }
            switch (checkedId) {
                case R.id.rb_home:
                    position = 0;
                    break;
    
                case R.id.rb_course:
                    position = 1;
                    break;
    
                case R.id.rb_direct_seeding:
                    position = 2;
                    break;
    
                case R.id.rb_me:
                    position = 3;
                    break;
                default:
                    position = 0;
                    break;
    
            }
            mViewPager.setCurrentItem(position);
        }
    });

### 注意事项 ###

我们可以通过以下方法设置ViewPager左右页面 能缓存的fragment 数量

// 设置左右页面 能缓存的fragment 数量
    mViewPager.setOffscreenPageLimit(fragmentAdapter.getCount() - 1);

--------------------

到此仿qq底部tab切换的集中方法已经讲解完毕，之所以讲解了 三种方法，是想让大家了解多种实现方式，因为每一个人的习惯都不一样，有些人习惯使用与第一种方式，有人习惯使用第二种方式 。。。。。。了解多种 实现方式以后，我们要读懂别人的代码也容易得多了，其实我们还可以使用自定义控件来实现，方法也比较简单，这里就不讲解了，有兴趣的话，可以自行搜索

下面我将为大家讲解Fragment的 一些优化

--------------------

## 解决Fragment多次实例化的几种方案 ##

目前本人了解到的解决方案 ，无非是利用一下两种思想

### 第一种解决方法 ###

在onCreateView中避免多次实例化View，可通过判断View是否为空，来实现相应的 逻辑操作,核心代码如下

public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable
                Bundle savedInstanceState) {
            LUtils.i(getClass().getSimpleName()+">>>>>>>>>>>　　onCreateView");
            if(mView==null){
                mContext = getContext();
                mView=View.inflate(mContext,getLayoutId(),null);
                initView(mView);
                LUtils.i(getClass().getSimpleName()+">>>>>>>>>>>　　initView");
            }else{
                // 缓存的rootView需要判断是否已经被加过parent，如果有parent需要从parent删除，
                // 要不然会发生这个rootview已经有parent的错误。
                ViewGroup parent =(ViewGroup) mView.getParent();
                if(parent!=null){
                    parent.removeView(mView);
                }
                LUtils.i(getClass().getSimpleName()+">>>>>>>>>>>　　removeView");
            }
            return mView;
        }

### 第二种解决方案 ###

在项目中需要进行Fragment的切换，用hide（）和show（）方法结合起来来替代replace()方法来实现Fragment的切换：

private void showFragment(Fragment from, Fragment to) {
        FragmentManager supportFragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = supportFragmentManager.beginTransaction();
        if (!to.isAdded()) {    // 先判断是否被add过
            transaction.hide(from).add(R.id.fl, to).commit(); // 隐藏当前的fragment，add下一个到Activity中
        } else {
            transaction.hide(from).show(to).commit(); // 隐藏当前的fragment，显示下一个
        }
    
    }
    
    /** * 这个方法用老替换fragment * xujun * 2016/5/3 17:28. */
    
    private void replaceFragment(Fragment fragmeny) {
        FragmentManager supportFragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = supportFragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.fl, fragmeny).commit();
    }

关于 避免Fragment的多次实例化的分析与优化到此为止，下面我们一起来看一下 则那样实现Fragemnt 的 懒加载

--------------------

## Fragemnt的懒加载（网上很多人称之为Fragemnt的最优加载） ##

关于懒加载的这部分，代码是参考这篇 博客的 [ViewPager+Fragment LazyLoad最优解][ViewPager_Fragment LazyLoad]

我们知道 ViewPager通常 会有预加载机制，默认情况下会先加载左右一页的数据，有时候我们想等待页面可见的时候在去加载网络 数据 ，解决方案如下

下面 先贴出代码

public abstract class BasePageFragment extends Fragment { 
    
        protected View mView;
    
        /** * 表示View是否被初始化 */
        protected boolean isViewInitiated;
        /** * 表示对用户是否可见 */
        protected boolean isVisibleToUser;
        /** * 表示数据是否初始化 */
        protected boolean isDataInitiated;
        private Context mContext;
    
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            LUtils.i(getClass().getSimpleName() + ">>>>>>>>>>>　　onCreate");
        }
    
        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable
                Bundle savedInstanceState) {
            LUtils.i(getClass().getSimpleName() + ">>>>>>>>>>>　　onCreateView");
            if (mView == null) {
                mContext = getContext();
                mView = View.inflate(mContext, getLayoutId(), null);
                initView(mView);
                LUtils.i(getClass().getSimpleName() + ">>>>>>>>>>>　　initView");
            } else {
                // 缓存的rootView需要判断是否已经被加过parent，如果有parent需要从parent删除，
                // 要不然会发生这个rootview已经有parent的错误。
                ViewGroup parent = (ViewGroup) mView.getParent();
                if (parent != null) {
                    parent.removeView(mView);
                }
                LUtils.i(getClass().getSimpleName() + ">>>>>>>>>>>　　removeView");
            }
            return mView;
        }
    
        protected abstract void initView(View view);
    
        protected abstract int getLayoutId();
    
        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            LUtils.i(getClass().getSimpleName() + ">>>>>>>>>>>　　onActivityCreated");
            isViewInitiated = true;
            initData();
            prepareFetchData();
        }
    
        @Override
        public void setUserVisibleHint(boolean isVisibleToUser) {
            super.setUserVisibleHint(isVisibleToUser);
            this.isVisibleToUser = isVisibleToUser;
            prepareFetchData();
        }
    
        public abstract void fetchData();
    
        public boolean prepareFetchData() {
            return prepareFetchData(false);
        }
    
        /*** * * @param forceUpdate 表示是否在界面可见的时候是否强制刷新数据 * @return */
        public boolean prepareFetchData(boolean forceUpdate) {
            if (isVisibleToUser && isViewInitiated && (!isDataInitiated || forceUpdate)) {
                // 界面可见的时候再去加载数据
                fetchData();
                isDataInitiated = true;
                return true;
            }
            return false;
        }
    
        @Override
        public void onDestroyView() {
            super.onDestroyView();
            LUtils.i(getClass().getSimpleName() + ">>>>>>>>>>>　　onDestroyView");
        }
    
        protected void initData() {
        }
    
    }

思路解析：  
其实核心思想主要在setUserVisibleHint(boolean isVisibleToUser)方法中，这个方法在Fragemnt界面切换到可见或者 不可见的时候调用，isVisibleToUser表示当前界面可见 或者不可见

> setUserVisibleHint(boolean isVisibleToUser)
> 
> Set a hint to the system about whether this fragment’s UI is currently visible to the user.

于是我们在prepareFetchData进行判断只有当界面可见的情况下才会尝试判断是否调用fetchData() 方法，于是我们就可以实现等到界面可见的 时候才加载网络数据，将我们加载网络数据的 逻辑的实现放在fetchData()  
里面即可

/*** * * @param forceUpdate 表示是否在界面可见的时候是否强制刷新数据 * @return */
    public boolean prepareFetchData(boolean forceUpdate) {
        if (isVisibleToUser && isViewInitiated && (!isDataInitiated || forceUpdate)) {
            // 界面可见的时候再去加载数据
            fetchData();
            isDataInitiated = true;
            return true;
        }
        return false;
    }

## 题外话 ##

转眼间校招季已经过去了一个多月了，虽然没能进入到bat，网易之类的公司，不过也找到了相对比较喜欢的公司，接下来的日子就专心做毕业设计了，计划在十一月的时候出省旅游一次，明年春节回来的时候再去公司实习，悄悄地告诉你一件事哦，本人 还没有 出过广东省 ，哈哈，是不是很low呢？

**[转载请注明博客地址：][Link 1][http://blog.csdn.net/gdutxiaoxu/article/details/52826810][Link 1]**

**[源码下载地址：][Link 2][https://github.com/gdutxiaoxu/QQBottomTab.git][Link 2]**

[9fe4afa0jw1f8szzo4g0rg209c0gdq4i.gif]: /images/20220716/db33600e19b14f90b1ec5db16c5243b0.png
[9fe4afa0gw1f8t00ub0hng208l0ekabn.gif]: /images/20220716/69d2f6bdcff543dd9c09246f4cb10ffe.png
[ViewPager_Fragment LazyLoad]: http://www.jianshu.com/p/c5d29a0c3f4c
[Link 1]: http://blog.csdn.net/gdutxiaoxu/article/details/52826810
[Link 2]: https://github.com/gdutxiaoxu/QQBottomTab.git