Fragments 誕生初衷

? ? ?自從Android 3.0中引入fragments 的概念,根據詞海的翻譯可以譯為:碎片、片段。其上的是為了解決不同屏幕分辯率的動態和靈活UI設計。大屏幕如平板小屏幕如手機，平板電腦的設計使得其有更多的空間來放更多的UI組件，而多出來的空間存放UI使其會產生更多的交互，從而誕生了fragments 。fragments 的設計不需要你來親自管理view hierarchy 的復雜變化，通過將Activity 的布局分散到frament 中，可以在運行時修改activity 的外觀，并且由activity 管理的back stack 中保存些變化。

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? ? ? Fragments 設計理念

? ? ? 在設計應用時特別是Android 應用 ，有眾多的分辨率要去適應，而fragments 可以讓你在屏幕不同的屏幕上動態管理UI。例如：通訊應用程序（QQ），用戶列表可以在左邊，消息窗口在右邊的設計。而在手機屏幕用戶列表填充屏幕當點擊某一用戶時，則彈出對話窗口的設計，如下圖：

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Fragments的生命周期?

? ? 每一個fragments 都有自己的一套生命周期回調方法和處理自己的用戶輸入事件。 對應生命周期可參考下圖：

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?其中大多數程序必須使用Fragments 必須實現的三個回調方法分別為：

onCreate

? ?系統創建Fragments 時調用，可做執行初始化工作或者當程序被暫停或停止時用來恢復狀態，跟Activity 中的onCreate相當。?

onCreateView

? ?用于首次繪制用戶界面的回調方法，必須返回要創建的Fragments 視圖UI。假如你不希望提供Fragments 用戶界面則可以返回NULL。?

onPause?

? ? 當用戶離開這個Fragments 的時候調用，這時你要提交任何應該持久的變化，因為用戶可能不會回來。更多的事件可以參考上圖的生命周期關系圖。

Fragments 的類別

? ? 系統內置了三種Fragments ，這三種Fragments 分別有不同的應用場景分別為：

DialogFragment

?對話框式的Fragments，可以將一個fragments 對話框并到activity 管理的fragments back stack 中，允許用戶回到一個前曾摒棄fragments.

ListFragments

? ?類似于ListActivity 的效果，并且還提供了ListActivity 類似的onListItemCLick和setListAdapter等功能。

PreferenceFragments

? ?類似于PreferenceActivity .可以創建類似IPAD的設置界面。?

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Fragments 的詳細使用?

? ? 首先先來看一張DEMO 效果圖：

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? ? 左邊點擊時，右邊的字符會與左邊選中的項的字符相同。與IPAD上的設置界面很相似，這一點是否借鑒了ipad 上的UI呢？

相就的XML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="horizontal"?>

???<fragment?class="com.xuzhi.fragment.FragmentDemoActivity$TitlesFragment"?android:id="@+id/titles"?android:layout_weight="1"
???????android:layout_width="0px"?android:layout_height="match_parent"
???????/>
???
???<FrameLayout?android:id="@+id/details"?android:layout_weight="1"?android:layout_width="0px"?android:layout_height="match_parent"
???????android:background="?android:attr/detailsElementBackground"
???????></FrameLayout>
</LinearLayout> 復制代碼

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主界面代碼（己做注釋）：

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package?com.xuzhi.fragment;
import?android.app.Activity;
import?android.app.AlertDialog;
import?android.app.Fragment;
import?android.app.FragmentTransaction;
import?android.app.ListFragment;
import?android.os.Bundle;
import?android.util.TypedValue;
import?android.view.LayoutInflater;
import?android.view.View;
import?android.view.ViewGroup;
import?android.widget.ArrayAdapter;
import?android.widget.ListView;
import?android.widget.ScrollView;
import?android.widget.TextView;

public?class?FragmentDemoActivity?extends?Activity?{

????public?static?String[]?array?=?{?"text1,",?"text2",?"text3",?"text4",
????????????"text5,",?"text6",?"text7",?"text8"?};

????/**?Called?when?the?activity?is?first?created.?*/
????@Override
????public?void?onCreate(Bundle?savedInstanceState)?{
????????super.onCreate(savedInstanceState);?
????????setContentView(R.layout.main);
????}

????????
????public?static?class?TitlesFragment?extends?ListFragment?{

????????boolean?mDualPane;
????????int?mCurCheckPosition?=?0;
????????
????????@Override
????????public?void?onCreate(Bundle?savedInstanceState)?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onCreate(savedInstanceState);
????????????System.out.println("Fragment-->onCreate");
????????}
????????
????????@Override
????????public?View?onCreateView(LayoutInflater?inflater,?ViewGroup?container,
????????????????Bundle?savedInstanceState)?{
????????????//?TODO?Auto-generated?method?stub
????????????System.out.println("Fragment-->onCreateView");
????????????return?super.onCreateView(inflater,?container,?savedInstanceState);
????????}
????????
????????@Override
????????public?void?onPause()?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onPause();
????????????System.out.println("Fragment-->onPause");
????????}
????????
????????
????????@Override
????????public?void?onStop()?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onStop();
????????????
????????????System.out.println("Fragment-->onStop");
????????}
????????
????????@Override
????????public?void?onAttach(Activity?activity)?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onAttach(activity);
????????????System.out.println("Fragment-->onAttach");
????????}
????????
????????@Override
????????public?void?onStart()?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onStart();
????????????System.out.println("Fragment-->onStart");
????????}
????????
????????@Override
????????public?void?onResume()?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onResume();
????????????System.out.println("Fragment-->onResume");
????????}
????????
????????@Override
????????public?void?onDestroy()?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onDestroy();
????????????System.out.println("Fragment-->onDestroy");
????????}
????????
????????

????????@Override
????????public?void?onActivityCreated(Bundle?savedInstanceState)?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onActivityCreated(savedInstanceState);
????????????System.out.println("Fragment-->onActivityCreted");
????????????setListAdapter(new?ArrayAdapter<String>(getActivity(),
????????????????????android.R.layout.simple_list_item_1,?array));

????????????View?detailsFrame?=?getActivity().findViewById(R.id.details);

????????????mDualPane?=?detailsFrame?!=?null
????????????????????&&?detailsFrame.getVisibility()?==?View.VISIBLE;

????????????if?(savedInstanceState?!=?null)?{
????????????????mCurCheckPosition?=?savedInstanceState.getInt("curChoice",?0);?//從保存的狀態中取出數據
????????????}

????????????if?(mDualPane)?{
????????????????getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);

????????????????showDetails(mCurCheckPosition);
????????????}
????????}

????????@Override
????????public?void?onSaveInstanceState(Bundle?outState)?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onSaveInstanceState(outState);

????????????outState.putInt("curChoice",?mCurCheckPosition);//保存當前的下標
????????}

????????@Override
????????public?void?onListItemClick(ListView?l,?View?v,?int?position,?long?id)?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onListItemClick(l,?v,?position,?id);
????????????showDetails(position);
????????}

????????void?showDetails(int?index)?{
????????????mCurCheckPosition?=?index;?
????????????if?(mDualPane)?{
????????????????getListView().setItemChecked(index,?true);
????????????????DetailsFragment?details?=?(DetailsFragment)?getFragmentManager()
????????????????????????.findFragmentById(R.id.details);?
????????????????if?(details?==?null?||?details.getShownIndex()?!=?index)?{
????????????????????details?=?DetailsFragment.newInstance(mCurCheckPosition);?

????????????????????//得到一個fragment?事務（類似sqlite的操作）
????????????????????FragmentTransaction?ft?=?getFragmentManager()
????????????????????????????.beginTransaction();
????????????????????ft.replace(R.id.details,?details);//將得到的fragment?替換當前的viewGroup內容，add則不替換會依次累加
????????????????????ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);//設置動畫效果
????????????????????ft.commit();//提交
????????????????}
????????????}?else?{
????????????????new?AlertDialog.Builder(getActivity()).setTitle(
????????????????????????android.R.string.dialog_alert_title).setMessage(
????????????????????????array[index]).setPositiveButton(android.R.string.ok,
????????????????????????null).show();
????????????}
????????}
????}

????/**
?????*?作為界面的一部分，為fragment?提供一個layout
?????*?@author?terry
?????*
?????*/
????public?static?class?DetailsFragment?extends?Fragment?{

????????public?static?DetailsFragment?newInstance(int?index)?{?
????????????DetailsFragment?details?=?new?DetailsFragment();
????????????Bundle?args?=?new?Bundle();
????????????args.putInt("index",?index);
????????????details.setArguments(args);
????????????return?details;
????????}

????????public?int?getShownIndex()?{
????????????return?getArguments().getInt("index",?0);
????????}

????????@Override
????????public?View?onCreateView(LayoutInflater?inflater,?ViewGroup?container,
????????????????Bundle?savedInstanceState)?{
????????????//?TODO?Auto-generated?method?stub
????????????if?(container?==?null)
????????????????return?null;

????????????ScrollView?scroller?=?new?ScrollView(getActivity());
????????????TextView?text?=?new?TextView(getActivity());

????????????int?padding?=?(int)?TypedValue.applyDimension(
????????????????????TypedValue.COMPLEX_UNIT_DIP,?4,?getActivity()
????????????????????????????.getResources().getDisplayMetrics());
????????????text.setPadding(padding,?padding,?padding,?padding);
????????????scroller.addView(text);

????????????text.setText(array[getShownIndex()]);
????????????return?scroller;
????????}
????}
} 復制代碼

?注意：

?

如果你想在Fragment 里面創建menu，則必須在onCreate的時候設置讓它可以存在optionMenu才可以創建，代碼為：
public?static?class?DetailsFragment?extends?Fragment?{

????????@Override
????????public?void?onCreate(Bundle?savedInstanceState)?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onCreate(savedInstanceState);
????????????setHasOptionsMenu(true);
????????}
} 復制代碼 之后的操作即可以像平常Android的menu用法一樣,代碼為：
@Override
????????public?void?onCreateOptionsMenu(Menu?menu,?MenuInflater?inflater)?{
????????????//?TODO?Auto-generated?method?stub
????????????super.onCreateOptionsMenu(menu,?inflater);
?????????????menu.add("Menu?1a").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
????????????????menu.add("Menu?1b").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);
????????}
????????
????????@Override
????????public?boolean?onOptionsItemSelected(MenuItem?item)?{
????????????//?TODO?Auto-generated?method?stub
????????????Toast.makeText(getActivity(),?"index?is"+getShownIndex()+"?&&?menu?text?is?"+item.getTitle(),?1000).show();
????????????return?super.onOptionsItemSelected(item);
????????} 復制代碼

?更多詳細的使用方法，請參考SDK和APIDEMO中相關的例子和解釋。

DEMO下載：

Android FramentDEMO?

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本文出自 “Terry_龍” 博客，請務必保留此出處http://terryblog.blog.51cto.com/1764499/793310

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