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写的是简易版的Fragment应用，在一个主layout（activty_main.layout）中添加一个fragment。因为
需要继承 android.support.v4.app.Fragment ，Fragment类 需要实现的方法：
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
通过下列语句实现创建一个View实例并返回，
View v = (View) inflater.inflate(R.layout.crime_fragment,container,false);
参数分别是：布局文件，父组件，是否关联
1 package com.example.fragmentpractise; 2 3 import java.util.UUID; 4 5 import android.os.Bundle; 6 import android.support.v4.app.Fragment; 7 import android.util.Log; 8 import android.view.LayoutInflater; 9 import android.view.View; 10 import android.view.ViewGroup; 11 import android.widget.Button; 12 13 public class CrimeFragment extends Fragment{ 14 15 private Crime mCrime; 16 17 public static CrimeFragment newInstance(int id){ 18 CrimeFragment c = new CrimeFragment(); 19 return c; 20 } 21 22 @Override 23 public void onCreate(Bundle savedInstanceState){ 24 super.onCreate(savedInstanceState); 25 mCrime = new Crime(); 26 } 27 28 @Override 29 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){ 30 31 View v = (View) inflater.inflate(R.layout.crime_fragment,container,false); 32 Button date = (Button) v.findViewById(R.id.date); 33 date.setText(mCrime.getDate().toString()); 34 return v; 35 36 } 37 38 }
1 <?xml version="1.0" encoding="utf-8"?> 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 3 android:layout_width="match_parent" 4 android:layout_height="match_parent" 5 android:orientation="vertical" > 6 <TextView 7 android:layout_width="match_parent" 8 android:layout_height="wrap_content" 9 android:textSize="20dp" 10 android:text="@string/title_label"/> 11 <EditText 12 android:id="@+id/title" 13 android:layout_width="match_parent" 14 android:layout_height="wrap_content" 15 android:textSize="16dp" 16 /> 17 <TextView 18 android:layout_width="match_parent" 19 android:layout_height="wrap_content" 20 android:textSize="20dp" 21 android:text="@string/detail_label"/> 22 <Button 23 android:id="@+id/date" 24 android:layout_width="match_parent" 25 android:layout_height="wrap_content" 26 /> 27 <CheckBox 28 android:id="@+id/isSolved" 29 android:layout_width="match_parent" 30 android:layout_height="wrap_content" 31 android:text="@string/isSolved"/> 32 33 </LinearLayout>
在启动类中实现通过FragmentManager调用 findFragmentById(id) 查找是否存在，最后通过事务提交Fragment
1 @Override 2 protected void onCreate(Bundle savedInstanceState) { 3 super.onCreate(savedInstanceState); 4 setContentView(R.layout.activity_crime); 5 FragmentManager fm = getSupportFragmentManager() ; 6 Fragment fragment = fm.findFragmentById(R.id.fragment_container); 7 if(fragment == null){ 8 FragmentTransaction tran = fm.beginTransaction (); 9 tran.add(R.id.fragment_container,new CrimeFragment()); 10 tran.commit(); 11 }
Finds a fragment that was identified by the given id either when inflated from XML or as the container ID when added in a transaction. This first searches through fragments that are currently added to the manager‘s activity; if no such fragment is found, then all fragments currently on the back stack associated with this ID are searched.
The fragment if found or null otherwise.
这个方法实现了从FragmentManager实例中去寻找一个符合条件的Fragment,这里的条件受id制约，但API提到id究竟是什么呢？尝试使用了传入提交事务时的id，或者是生成布局时的给设置的id,最后在生成视图去检测都依旧不行；
为了验证这一方法，以下代码分别验证了通过Fragmentd XML的id来搜索：
1 @Override 2 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){ 3 4 View v = (View) inflater.inflate(R.layout.crime_fragment,container,false); 5 Button date = (Button) v.findViewById(R.id.date); 6 date.setText(mCrime.getDate().toString()); 7 v.setId(R.id.test); 8 return v; 9 10 }
1 fragment = fm.findFragmentById(R.id.test); 2 if(fragment != null){ 3 Log.i("information", "true"); 4 } else{ 5 Log.i("information","false"); 6 }
结果是：10-13 23:10:16.267: I/information(2997): false
直到后来求助了高手和查阅资料后，终于发现了问题所在：这个提交的动作并不是同步的，由事务提交请求，再由系统自己去处理，为了验证这个问题，使用了以下代码来验证：
1 FragmentManager fm = getSupportFragmentManager() ; 2 Fragment fragment = fm.findFragmentById(R.id.fragment_container); 3 if(fragment == null){ 4 FragmentTransaction tran = fm.beginTransaction (); 5 tran.add(R.id.fragment_container,new CrimeFragment()); 6 tran.commit(); 7 }
1 Timer timer= new Timer(); 2 timer.schedule(new TimerTask() { 3 4 @Override 5 public void run() { 6 // TODO Auto-generated method stub 7 FragmentManager fm = getSupportFragmentManager() ; 8 Fragment fragment = fm.findFragmentById(R.id.fragment_container); 9 if(fragment != null){ 10 Log.i("information", "true"); 11 } else{ 12 Log.i("information","false"); 13 } 14 } 15 }, 2000);
结果是：10-14 22:18:47.436: I/information(1672): true
思路是使用线程，延迟2秒去检测。
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原文地址：http://www.cnblogs.com/lhppom/p/4876220.html
