【学习笔记】Android Fragments
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参考。
一些关键概念，如back stack和action bar，还不太明白。
正如 a portion of user interface in an Activity。
- A fragment must always be embedded in an activity and the fragment's lifecycle is directly affected by the host activity's lifecycle.
- When you add a fragment as a part of your activity layout, it lives in a ViewGroup inside the activity's view hierarchy and the fragment defines its own view layout.
- <fragment> element
- However, a fragment is not required to be a part of the activity layout; you may also use a fragment without its own UI as an invisible worker for the activity.
创建Fragment
从Fragment类派生。有一套和Activity非常接近的callback functions。
需要实现onCreate(), onCreateView(), onPause()等函数。
提供DialogFragmet, ListFragment, 和PreferenceFragmentCompat等常用的Fragment。
用户界面
onCreateView()函数用于绘制Fragmet的图形界面。该函数必须返回一个View对象。该View对象可以利用一个xml文件生成（inflate）。
将Fragment添加到Activity中
可以通过Activity的layout文件。注意<fragment> element的android:name属性为这个Fragment的JAVA类。
可以动态向Activity添加和删除Fragment，需要使用Android提供的FragmentTransaction。
也可以添加无UI的Fragment，此时不需要实现onCreateView()函数。但是需要指定一个Tag作为标志。
管理Fragment
需要使用FragmentManager。需要了解back stack。
通讯
Fragment可以和Activity中的其他View对象进行通讯，利用FragmentActivity获取这些View对象。
Activity可以访问Fragment的函数，通过FragmentManager。
Event
Fragment可以指定Activity实现某些函数，已实现Event的传递。
App Bar
Your fragments can contribute menu items to the activity's Options Menu (and, consequently, the app bar) by implementing onCreateOptionsMenu().
实例
该实例大部分是从复制而来，但是原文中TitlesFragment类的showDetails()函数存在错误，在google上找了一阵子，最终在stackoverflow的一个问题中找到了答案，是一个bug。下面给出的源代码已经修正了该问题。
该实例已经在API22中得到测试，并在ADV中调试成功。所使用的package前缀为com.huyaoyu，project名为TestFragment。
首先是res/layout/fragment_layout.xml
接下来是res/layout-land/fragmet_layout.xml
以下是AndroidManifest.xml
然后是FragmentLayout.java
package com.huyaoyu.testfragment;import android.app.Activity;import android.app.Fragment;import android.app.FragmentTransaction;import android.app.ListFragment;import android.content.Intent;import android.content.res.Configuration;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;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 FragmentLayout extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.fragment_layout); } public static class TitlesFragment extends ListFragment { boolean mDualPane; int mCurCheckPosition = 0; @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); // Populate list with our static array of titles. setListAdapter(new ArrayAdapter (getActivity(), android.R.layout.simple_list_item_activated_1, Shakespeare.TITLES)); // Check to see if we have a frame in which to embed the details // fragment directly in the containing UI. View detailsFrame = getActivity().findViewById(R.id.details); mDualPane = detailsFrame != null && detailsFrame.getVisibility() == View.VISIBLE; if (savedInstanceState != null) { // Restore last state for checked position. mCurCheckPosition = savedInstanceState.getInt("curChoice", 0); } if (mDualPane) { // In dual-pane mode, the list view highlights the selected item. getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE); // Make sure our UI is in the correct state. showDetails(mCurCheckPosition); } } @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); outState.putInt("curChoice", mCurCheckPosition); } @Override public void onListItemClick(ListView l, View v, int position, long id) { showDetails(position); } /** * Helper function to show the details of a selected item, either by * displaying a fragment in-place in the current UI, or starting a * whole new activity in which it is displayed. */ void showDetails(int index) { mCurCheckPosition = index; if (mDualPane) { // We can display everything in-place with fragments, so update // the list to highlight the selected item and show the data. getListView().setItemChecked(index, true); // Check what fragment is currently shown, replace if needed. DetailsFragment details = (DetailsFragment) getFragmentManager().findFragmentById(R.id.details); if (details == null || details.getShownIndex() != index) { // Make new fragment to show this selection. details = DetailsFragment.newInstance(index); // Execute a transaction, replacing any existing fragment // with this one inside the frame. FragmentTransaction ft = getFragmentManager().beginTransaction(); /* The following line is the modified version of the original ApiDemo. The modification is found at the following websites. Thanks to stackoverflow! https://stackoverflow.com/questions/22075775/android-fragment-query-regarding-resource-r-id-a-item-definition https://issuetracker.google.com/issues/36970064 */ ft.replace(R.id.details, details); ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE); ft.commit(); } } else { // Otherwise we need to launch a new activity to display // the dialog fragment with selected text. Intent intent = new Intent(); intent.setClass(getActivity(), DetailsActivity.class); intent.putExtra("index", index); startActivity(intent); } } } public static class DetailsFragment extends Fragment { /** * Create a new instance of DetailsFragment, initialized to * show the text at 'index'. */ public static DetailsFragment newInstance(int index) { DetailsFragment f = new DetailsFragment(); // Supply index input as an argument. Bundle args = new Bundle(); args.putInt("index", index); f.setArguments(args); return f; } public int getShownIndex() { return getArguments().getInt("index", 0); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { if (container == null) { // We have different layouts, and in one of them this // fragment's containing frame doesn't exist. The fragment // may still be created from its saved state, but there is // no reason to try to create its view hierarchy because it // won't be displayed. Note this is not needed -- we could // just run the code below, where we would create and return // the view hierarchy; it would just never be used. 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(Shakespeare.DIALOGUE[getShownIndex()]); return scroller; } } public static class DetailsActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); if (getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE) { // If the screen is now in landscape mode, we can show the // dialog in-line with the list so we don't need this activity. finish(); return; } if (savedInstanceState == null) { // During initial setup, plug in the details fragment. DetailsFragment details = new DetailsFragment(); details.setArguments(getIntent().getExtras()); getFragmentManager().beginTransaction().add(android.R.id.content, details).commit(); } } }} 最后是Shakespeare.java
package com.huyaoyu.testfragment;/** * Created by yaoyu on 2/25/18. * * The content is copied directly from * https://github.com/aosp-mirror/platform_development/blob/ef7ff204e2ad4ba1094db8e9dc891a13c1f7ba31/samples/ApiDemos/src/com/example/android/apis/Shakespeare.java * */public final class Shakespeare { /** * Our data, part 1. */ public static final String[] TITLES = { "Henry IV (1)", "Henry V", "Henry VIII", "Richard II", "Richard III", "Merchant of Venice", "Othello", "King Lear" }; /** * Our data, part 2. */ public static final String[] DIALOGUE = { "So shaken as we are, so wan with care," + "Find we a time for frighted peace to pant," + "And breathe short-winded accents of new broils" + "To be commenced in strands afar remote." + "No more the thirsty entrance of this soil" + "Shall daub her lips with her own children's blood;" + "Nor more shall trenching war channel her fields," + "Nor bruise her flowerets with the armed hoofs" + "Of hostile paces: those opposed eyes," + "Which, like the meteors of a troubled heaven," + "All of one nature, of one substance bred," + "Did lately meet in the intestine shock" + "And furious close of civil butchery" + "Shall now, in mutual well-beseeming ranks," + "March all one way and be no more opposed" + "Against acquaintance, kindred and allies:" + "The edge of war, like an ill-sheathed knife," + "No more shall cut his master. Therefore, friends," + "As far as to the sepulchre of Christ," + "Whose soldier now, under whose blessed cross" + "We are impressed and engaged to fight," + "Forthwith a power of English shall we levy;" + "Whose arms were moulded in their mothers' womb" + "To chase these pagans in those holy fields" + "Over whose acres walk'd those blessed feet" + "Which fourteen hundred years ago were nail'd" + "For our advantage on the bitter cross." + "But this our purpose now is twelve month old," + "And bootless 'tis to tell you we will go:" + "Therefore we meet not now. Then let me hear" + "Of you, my gentle cousin Westmoreland," + "What yesternight our council did decree" + "In forwarding this dear expedience.", "Hear him but reason in divinity," + "And all-admiring with an inward wish" + "You would desire the king were made a prelate:" + "Hear him debate of commonwealth affairs," + "You would say it hath been all in all his study:" + "List his discourse of war, and you shall hear" + "A fearful battle render'd you in music:" + "Turn him to any cause of policy," + "The Gordian knot of it he will unloose," + "Familiar as his garter: that, when he speaks," + "The air, a charter'd libertine, is still," + "And the mute wonder lurketh in men's ears," + "To steal his sweet and honey'd sentences;" + "So that the art and practic part of life" + "Must be the mistress to this theoric:" + "Which is a wonder how his grace should glean it," + "Since his addiction was to courses vain," + "His companies unletter'd, rude and shallow," + "His hours fill'd up with riots, banquets, sports," + "And never noted in him any study," + "Any retirement, any sequestration" + "From open haunts and popularity.", "I come no more to make you laugh: things now," + "That bear a weighty and a serious brow," + "Sad, high, and working, full of state and woe," + "Such noble scenes as draw the eye to flow," + "We now present. Those that can pity, here" + "May, if they think it well, let fall a tear;" + "The subject will deserve it. Such as give" + "Their money out of hope they may believe," + "May here find truth too. Those that come to see" + "Only a show or two, and so agree" + "The play may pass, if they be still and willing," + "I'll undertake may see away their shilling" + "Richly in two short hours. Only they" + "That come to hear a merry bawdy play," + "A noise of targets, or to see a fellow" + "In a long motley coat guarded with yellow," + "Will be deceived; for, gentle hearers, know," + "To rank our chosen truth with such a show" + "As fool and fight is, beside forfeiting" + "Our own brains, and the opinion that we bring," + "To make that only true we now intend," + "Will leave us never an understanding friend." + "Therefore, for goodness' sake, and as you are known" + "The first and happiest hearers of the town," + "Be sad, as we would make ye: think ye see" + "The very persons of our noble story" + "As they were living; think you see them great," + "And follow'd with the general throng and sweat" + "Of thousand friends; then in a moment, see" + "How soon this mightiness meets misery:" + "And, if you can be merry then, I'll say" + "A man may weep upon his wedding-day.", "First, heaven be the record to my speech!" + "In the devotion of a subject's love," + "Tendering the precious safety of my prince," + "And free from other misbegotten hate," + "Come I appellant to this princely presence." + "Now, Thomas Mowbray, do I turn to thee," + "And mark my greeting well; for what I speak" + "My body shall make good upon this earth," + "Or my divine soul answer it in heaven." + "Thou art a traitor and a miscreant," + "Too good to be so and too bad to live," + "Since the more fair and crystal is the sky," + "The uglier seem the clouds that in it fly." + "Once more, the more to aggravate the note," + "With a foul traitor's name stuff I thy throat;" + "And wish, so please my sovereign, ere I move," + "What my tongue speaks my right drawn sword may prove.", "Now is the winter of our discontent" + "Made glorious summer by this sun of York;" + "And all the clouds that lour'd upon our house" + "In the deep bosom of the ocean buried." + "Now are our brows bound with victorious wreaths;" + "Our bruised arms hung up for monuments;" + "Our stern alarums changed to merry meetings," + "Our dreadful marches to delightful measures." + "Grim-visaged war hath smooth'd his wrinkled front;" + "And now, instead of mounting barded steeds" + "To fright the souls of fearful adversaries," + "He capers nimbly in a lady's chamber" + "To the lascivious pleasing of a lute." + "But I, that am not shaped for sportive tricks," + "Nor made to court an amorous looking-glass;" + "I, that am rudely stamp'd, and want love's majesty" + "To strut before a wanton ambling nymph;" + "I, that am curtail'd of this fair proportion," + "Cheated of feature by dissembling nature," + "Deformed, unfinish'd, sent before my time" + "Into this breathing world, scarce half made up," + "And that so lamely and unfashionable" + "That dogs bark at me as I halt by them;" + "Why, I, in this weak piping time of peace," + "Have no delight to pass away the time," + "Unless to spy my shadow in the sun" + "And descant on mine own deformity:" + "And therefore, since I cannot prove a lover," + "To entertain these fair well-spoken days," + "I am determined to prove a villain" + "And hate the idle pleasures of these days." + "Plots have I laid, inductions dangerous," + "By drunken prophecies, libels and dreams," + "To set my brother Clarence and the king" + "In deadly hate the one against the other:" + "And if King Edward be as true and just" + "As I am subtle, false and treacherous," + "This day should Clarence closely be mew'd up," + "About a prophecy, which says that 'G'" + "Of Edward's heirs the murderer shall be." + "Dive, thoughts, down to my soul: here" + "Clarence comes.", "To bait fish withal: if it will feed nothing else," + "it will feed my revenge. He hath disgraced me, and" + "hindered me half a million; laughed at my losses," + "mocked at my gains, scorned my nation, thwarted my" + "bargains, cooled my friends, heated mine" + "enemies; and what's his reason? I am a Jew. Hath" + "not a Jew eyes? hath not a Jew hands, organs," + "dimensions, senses, affections, passions? fed with" + "the same food, hurt with the same weapons, subject" + "to the same diseases, healed by the same means," + "warmed and cooled by the same winter and summer, as" + "a Christian is? If you prick us, do we not bleed?" + "if you tickle us, do we not laugh? if you poison" + "us, do we not die? and if you wrong us, shall we not" + "revenge? If we are like you in the rest, we will" + "resemble you in that. If a Jew wrong a Christian," + "what is his humility? Revenge. If a Christian" + "wrong a Jew, what should his sufferance be by" + "Christian example? Why, revenge. The villany you" + "teach me, I will execute, and it shall go hard but I" + "will better the instruction.", "Virtue! a fig! 'tis in ourselves that we are thus" + "or thus. Our bodies are our gardens, to the which" + "our wills are gardeners: so that if we will plant" + "nettles, or sow lettuce, set hyssop and weed up" + "thyme, supply it with one gender of herbs, or" + "distract it with many, either to have it sterile" + "with idleness, or manured with industry, why, the" + "power and corrigible authority of this lies in our" + "wills. If the balance of our lives had not one" + "scale of reason to poise another of sensuality, the" + "blood and baseness of our natures would conduct us" + "to most preposterous conclusions: but we have" + "reason to cool our raging motions, our carnal" + "stings, our unbitted lusts, whereof I take this that" + "you call love to be a sect or scion.", "Blow, winds, and crack your cheeks! rage! blow!" + "You cataracts and hurricanoes, spout" + "Till you have drench'd our steeples, drown'd the cocks!" + "You sulphurous and thought-executing fires," + "Vaunt-couriers to oak-cleaving thunderbolts," + "Singe my white head! And thou, all-shaking thunder," + "Smite flat the thick rotundity o' the world!" + "Crack nature's moulds, an germens spill at once," + "That make ingrateful man!" };} 目前使用的是Android Studio 3.0.1。ADV调试结果如下
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