Android Fragment使用

通常地 fragment做为宿主activity UI的一部分, 被作为activity整个view hierarchy的一部分被嵌入.<wbr>有2种方法你可以添加一个fragment到activity layout：</wbr>

一、在activity的layout文件中声明fragment

你可以像为View一样, 为fragment指定layout属性（sdk3.0以后）.

例子是一个有2个fragment的activity:

<?xml version="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

<wbr><span></span><wbr><span></span>android:orientation=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"horizontal"</span></wbr></wbr>

<wbr><span></span><wbr><span></span>android:layout_width=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"match_parent"</span></wbr></wbr>

<wbr><span></span><wbr><span></span>android:layout_height=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"match_parent"</span>&gt;</wbr></wbr>

<wbr><wbr><span></span><wbr><span></span>&lt;fragment android:name=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"com.example.news.ArticleListFragment"</span></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:id=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"@+id/list"</span></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:layout_weight=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"1"</span></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:layout_width=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"0dp"</span></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:layout_height=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"match_parent"</span><span></span>/&gt;</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><span></span><wbr><span></span>&lt;fragment android:name=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"com.example.news.ArticleReaderFragment"</span></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:id=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"@+id/viewer"</span></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:layout_weight=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"2"</span></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:layout_width=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"0dp"</span></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span><wbr><span></span>android:layout_height=<span style="color:#0910;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">"match_parent"</span><span></span>/&gt;</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><span></span><span style="color:#0091;line-height: 19px; word-break: normal; word-wrap: normal; background-color: inherit;">&lt;/LinearLayout&gt;</span></wbr>

<fragment> 中的 android:name 属性指定了在layout中实例化的Fragment类.<wbr></wbr>

当系统创建这个activity layout时, 它实例化每一个在layout中指定的fragment,并调用每一个上的onCreateView()方法,来获取每一个fragment的layout. 系统将从fragment返回的 View 直接插入到<fragment>元素所在的地方.<wbr></wbr>

注意: 每一个fragment都需要一个唯一的标识, 如果activity重启,系统可以用来恢复fragment(并且你也可以用来捕获fragment来处理事务,例如移除它.)<wbr></wbr>

有3种方法来为一个fragment提供一个标识:

• 为 android:id 属性提供一个唯一ID.
• 为 android:tag 属性提供一个唯一字符串.
• 如果以上2个你都没有提供, 系统使用容器view的ID.

二、使用FragmentManager将fragment添加到一个已存在的ViewGroup.

当activity运行的任何时候, 都可以将fragment添加到activity layout.只需简单的指定一个需要放置fragment的ViewGroup.为了在你的activity中操作fragment事务(例如添加,移除,或代替一个fragment),必须使用来自 FragmentTransaction 的API.

可以按如下方法,从你的Activity取得一个 FragmentTransaction 的实例:

FragmentManager fragmentManager = getFragmentManager();<wbr></wbr>
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

然后你可以使用 add() 方法添加一个fragment, 指定要添加的fragment, 和要插入的view.

ExampleFragment fragment =newExampleFragment();
 fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.commit();

add()的第一个参数是fragment要放入的ViewGroup, 由resource ID指定, 第二个参数是需要添加的fragment.一旦用FragmentTransaction做了改变,为了使改变生效,必须调用commit().

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* @author 张兴业
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