Fragment介绍和运用

为了在Android上为用户提供动态的、多窗口的交互体验，我们需要将UI组件和Activity操作封装成模块进行使用，使得我们可以在activity中对这些模块进行切入切出操作。可以用Fragment来创建这些模块，Fragment就像一个嵌套的activity，拥有自己的布局（layout）并管理自己的生命周期。

我们可以把fragment想象成activity中一个模块化的部分，它拥有自己的生命周期，接收自己的输入事件，可以在acvitity运行过程中添加或者移除（有点像”子activity”，可以在不同的activity里面重复使用）

对Fragment还不了解的同学可以参考博客Android Fragment完全解析介绍了Fragment的创建、静态添加、动态添加、生命周期和相互通信。

这里我们介绍如何用Fragment实现Tab切换的方法，假设大家已经撑握RadioGroup,RadioButton实现Tab选项卡.在学习FragmentTabHost之前可以参看TabHost主界面实现

FragmentTabHost实现

首先定义布局activity_raido_tab_fragment_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.app.FragmentTabHost xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/tabhost"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <TabWidget
            android:id="@android:id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:background="@color/gray_bg"
            android:divider="@null"
            android:visibility="gone" >
        </TabWidget>

        <RadioGroup
            android:id="@+id/raidoGroupTab"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:background="@drawable/button_color_confirm_selector"
            android:orientation="horizontal" >

            <RadioButton
                android:id="@+id/raidoTab1"
                style="@style/main_tab_bottom"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:drawableTop="@drawable/btn_tab_main"
                android:text="首页" />

            <RadioButton
                android:id="@+id/raidoTab2"
                style="@style/main_tab_bottom"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:drawableTop="@drawable/btn_tab_meishi"
                android:text="美食" />

            <RadioButton
                android:id="@+id/raidoTab3"
                style="@style/main_tab_bottom"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:drawableTop="@drawable/btn_tab_yule"
                android:text="娱乐" />
        </RadioGroup>

        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_above="@id/raidoGroupTab" >
        </FrameLayout>
    </RelativeLayout>

</android.support.v4.app.FragmentTabHost>

样式main_tab_bottom.xml

 <style name="main_tab_bottom">
        <item name="android:textSize">@dimen/bottom_tab_font_size</item>
        <item name="android:gravity">center_horizontal|bottom</item>
        <item name="android:paddingTop">@dimen/bottom_tab_padding_up</item>
        <item name="android:background">@drawable/home_btn_bg</item>
        <item name="android:paddingBottom">2.0dip</item>
        <item name="android:layout_width">fill_parent</item>
        <item name="android:layout_height">wrap_content</item>
        <item name="android:button">@null</item>
        <item name="android:drawablePadding">@dimen/bottom_tab_padding_drawable</item>
        <item name="android:layout_weight">1.0</item>
    </style>

代码

@Override
protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_raido_tab_fragment_layout);
	mRadioGroup = (RadioGroup) findViewById(R.id.raidoGroupTab);

	mTabHost = (FragmentTabHost) findViewById(android.R.id.tabhost);
	mTabHost.setup(this, getSupportFragmentManager(),android.R.id.tabcontent);

	mTabHost.addTab(mTabHost.newTabSpec("tab1").setIndicator("首页"),FragmentMain.class, null);
	mTabHost.addTab(mTabHost.newTabSpec("tab2").setIndicator("搜索"),FragmentSearch.class, null);
	mTabHost.addTab(mTabHost.newTabSpec("tab3").setIndicator("设置"),FragmentSetting.class, null);

	mRadioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {

		@Override
		public void onCheckedChanged(RadioGroup group, int checkedId) {
			switch (checkedId) {
			case R.id.raidoTab1:
				mTabHost.setCurrentTabByTag("tab1");
				break;
			case R.id.raidoTab2:
				mTabHost.setCurrentTabByTag("tab2");
				break;
			case R.id.raidoTab3:
				mTabHost.setCurrentTabByTag("tab3");
				break;
			}

		}
	});
	((RadioButton) mRadioGroup.getChildAt(0)).toggle(); //默认选中第一项
}

Fragment替换方法Replace实现

布局实现 fragment_tabs_replace_act.xml

<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:background="@drawable/bottom_bg"
    android:orientation="vertical" >

    <!-- 上边主页面 -->
    <FrameLayout
        android:id="@+id/fragments_content"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

    <!-- 底部菜单页面 -->
    <RadioGroup
        android:id="@+id/bottomRg"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:background="@drawable/maintab_toolbar_bg"
        android:orientation="horizontal" >

        <RadioButton
            android:id="@+id/rbOne"
            style="@style/main_tab_bottom"
            android:layout_marginTop="2.0dip"
            android:drawableTop="@drawable/icon_pinglun"
            android:text="首页" />

        <RadioButton
            android:id="@+id/rbTwo"
            style="@style/main_tab_bottom"
            android:layout_marginTop="2.0dip"
            android:drawableTop="@drawable/icon_xianshi"
            android:text="搜索" />

        <RadioButton
            android:id="@+id/rbThree"
            style="@style/main_tab_bottom"
            android:layout_marginTop="2.0dip"
            android:drawableTop="@drawable/icon_nongjiale"
            android:text="设置" />
    </RadioGroup>

</LinearLayout>

实现代码:

@Override
protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	requestWindowFeature(Window.FEATURE_NO_TITLE);
	setContentView(R.layout.fragment_tabs_replace_act);
	mRadioGroup = (RadioGroup) findViewById(R.id.bottomRg);

	mainFragment = (FragmentMain) FragmentMain.newInstance();
	searchFragment = (FragmentSearch) FragmentSearch.newInstance();
	settingFragment = (FragmentSetting) FragmentSetting.newInstance();

	mRadioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {

		@Override
		public void onCheckedChanged(RadioGroup group, int checkedId) {
			FragmentTransaction  fragmentTransaction = getSupportFragmentManager().beginTransaction();
			switch (checkedId) {
			case R.id.rbOne:
				if(mainFragment == null){
					mainFragment = (FragmentMain) FragmentMain.newInstance();
				}
				fragmentTransaction.replace(R.id.fragments_content, mainFragment);
				break;
			case R.id.rbTwo:
				if(searchFragment == null){
					searchFragment = (FragmentSearch) FragmentSearch.newInstance();
				}
				fragmentTransaction.replace(R.id.fragments_content, searchFragment);
				break;
			case R.id.rbThree:
				if(settingFragment == null){
					settingFragment = (FragmentSetting) FragmentSetting.newInstance();
				}
				fragmentTransaction.replace(R.id.fragments_content, settingFragment);
				break;
			}
			fragmentTransaction.commit();
		}
	});
	((RadioButton) mRadioGroup.getChildAt(0)).toggle(); // 默认选中第一项
}

Fragment替换方法每次切换Tab的时候实际是先移除(remove)再添加(add)Fragment,Fragment生命周期会从onAttach到onDetach

由上可知切换时，Fragment状态是不能保存的。FragmentSearch中EditText输入的值切换后便消失.

Fragment显示隐藏show和hide方法实现(解决状态存问题)
布局文件和上面一样

@Override
protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	requestWindowFeature(Window.FEATURE_NO_TITLE);
	setContentView(R.layout.fragment_tabs_replace_act);
	mRadioGroup = (RadioGroup) findViewById(R.id.bottomRg);

	mRadioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {

		@Override
		public void onCheckedChanged(RadioGroup group, int checkedId) {
			FragmentTransaction  fragmentTransaction = getSupportFragmentManager().beginTransaction();

			hideFragments(fragmentTransaction);

			switch (checkedId) {
			case R.id.rbOne:
				if(mainFragment == null){
					mainFragment = new FragmentMain();
					fragmentTransaction.add(R.id.fragments_content, mainFragment);
				}else{
					fragmentTransaction.show(mainFragment);
				}

				break;
			case R.id.rbTwo:
				if(searchFragment == null){
					searchFragment = new FragmentSearch();
					fragmentTransaction.add(R.id.fragments_content, searchFragment);
				}else{
					fragmentTransaction.show(searchFragment);
				}

				break;
			case R.id.rbThree:
				if(settingFragment == null){
					settingFragment = new FragmentSetting();
					fragmentTransaction.add(R.id.fragments_content, settingFragment);
				}else{
					fragmentTransaction.show(settingFragment);
				}

				break;
			}
			fragmentTransaction.commit();
		}
	});
	((RadioButton) mRadioGroup.getChildAt(0)).toggle(); // 默认选中第一项
	}

    /**
 * 将所有的Fragment都置为隐藏状态。
 *
 * @param transaction
 *            用于对Fragment执行操作的事务
 */
private void hideFragments(FragmentTransaction transaction) {
    if (mainFragment != null) {
        transaction.hide(mainFragment);
    }
    if (searchFragment != null) {
        transaction.hide(searchFragment);
    }
    if (settingFragment != null) {
        transaction.hide(settingFragment);
    }
}  

转载请注明来源：Fragment介绍和运用

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