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优雅的让Fragment监听返回键
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轉(zhuǎn)載請(qǐng)注明出處：http://write.blog.csdn.net/postedit/40507387
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Activity可以很容易的得到物理返回鍵的監(jiān)聽(tīng)事件，而Fragment卻不能。假設(shè)FragmentActivity有三個(gè)Fragment，一般安卓用戶期望點(diǎn)擊返回鍵會(huì)一層層返回到FragmentActivity。當(dāng)然，我們可以將每個(gè)Fragment對(duì)應(yīng)的Transaction放到BackStack中，但是如果每個(gè)Fragment有對(duì)返回事件的特殊消費(fèi)，那么在FragmentActivity的onBackPressed()中的代碼就會(huì)比較混亂，例如：
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@Override??public?void?onBackPressed()?{??????if(selectedFragment.equals(fragmentA)?&&?fragmentA.hasExpandedRow())?{??????????fragmentA.collapseRow();??????}?else?if(selectedFragment.equals(fragmentA)?&&?fragmentA.isShowingLoginView())?{??????????fragmentA.hideLoginView();??????}?else?if(selectedFragment.equals(fragmentA))?{??????????popBackStack();??????}?else?if(selectedFragment.equals(fragmentB)?&&?fragmentB.hasCondition1())?{??????????fragmentB.reverseCondition1();??????}?else?if(selectedFragment.equals(fragmentB)?&&?fragmentB.hasCondition2())?{??????????fragmentB.reverseCondition2();??????}?else?if(selectedFragment.equals(fragmentB))?{??????????popBackStack();??????}?else?{??????????????????super.onBackPressed();??????}??}?? 這對(duì)于有代碼潔癖的程序猿顯然是不能容忍的，后來(lái)發(fā)現(xiàn)了一種優(yōu)雅的解決方案。
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首先創(chuàng)建一個(gè)抽象類BackHandledFragment，該類有一個(gè)抽象方法onBackPressed()，所有BackHandledFragment的子類在onBackPressed方法中處理各自對(duì)Back事件的消費(fèi)邏輯。onBackPressed返回布爾值，宿主FragmentActivity將會(huì)根據(jù)該方法的返回值判斷子Fragment是否有消費(fèi)Back事件。此外，宿主FragmentActivity還會(huì)保持一份當(dāng)前Fragment的引用，當(dāng)用戶按下Back鍵時(shí)，宿主Activity會(huì)判斷當(dāng)前Fragment是否需要消費(fèi)該事件，如果沒(méi)有Fragment消費(fèi)才會(huì)自己消費(fèi)。
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public?abstract?class?BackHandledFragment?extends?Fragment?{????????protected?BackHandledInterface?mBackHandledInterface;????????????????protected?abstract?boolean?onBackPressed();????????????@Override??????public?void?onCreate(Bundle?savedInstanceState)?{??????????super.onCreate(savedInstanceState);??????????if(!(getActivity()?instanceof?BackHandledInterface)){??????????????throw?new?ClassCastException("Hosting?Activity?must?implement?BackHandledInterface");??????????}else{??????????????this.mBackHandledInterface?=?(BackHandledInterface)getActivity();??????????}??????}????????????@Override??????public?void?onStart()?{??????????super.onStart();??????????????????mBackHandledInterface.setSelectedFragment(this);??????}????????}?? 宿主FragmentActivity需要繼承BackHandledIntegerface，子Fragment會(huì)通過(guò)該接口告訴宿主FragmentActivity自己是當(dāng)前屏幕可見(jiàn)的Fragment。
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public?interface?BackHandledInterface?{????????public?abstract?void?setSelectedFragment(BackHandledFragment?selectedFragment);??}?? 所以在Fragment的onCreate中會(huì)判斷宿主FragmentActivity是否已繼承了該接口。在Fragment的onStart()方法中就會(huì)調(diào)用該接口告訴宿主FragmentActivity自己是當(dāng)前屏幕可見(jiàn)的Fragment。
宿主FragmentActivity就可以在onBackPressed()方法中對(duì)Back事件進(jìn)行判斷處理了。
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public?class?MainActivity?extends?FragmentActivity?implements?BackHandledInterface{????????private?BackHandledFragment?mBackHandedFragment;??????private?boolean?hadIntercept;????????@Override??????public?void?setSelectedFragment(BackHandledFragment?selectedFragment)?{??????????this.mBackHandedFragment?=?selectedFragment;??????}????????????@Override??????public?void?onBackPressed()?{??????????if(mBackHandedFragment?==?null?||?!mBackHandedFragment.onBackPressed()){??????????????if(getSupportFragmentManager().getBackStackEntryCount()?==?0){??????????????????super.onBackPressed();??????????????}else{??????????????????getSupportFragmentManager().popBackStack();??????????????}??????????}??????}??}?? ?
轉(zhuǎn)載于:https://www.cnblogs.com/xiaorenwu702/p/4561393.html
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