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Fragment英文翻译为碎片，可以在一个Activity中可以嵌套多个Fragment，相当于多个页面。但是它们都在同一 个Activity中，fragment的生命周期和Activity类似，如果当前Activity没有注销（onDestory）其中的众多的fragment也不会被销毁，这点不利于资源的回收。所以有时候你要考虑是使用多个fragment还是使用多个Activity。

[java] view plaincopy在CODE上查看代码片派生到我的代码片

1.可以在XML中编写，也可以在代码中编写，写一个类继承android.support.v4.app.Fragment，记住：是V4包中的Fragment.（考虑到版本的兼容性问题:fragment是Android3.0才引入的） 

2.重写父类Fragment的onCreate()，和onCreateView（）方法，onCreateView方法会返回一个VIew,这个View将被填充到Activity的界面中。所以一般我们重点就是把onCreateView()覆写好。 

3.在Acticvty中产生一个fragment的实例，调用fragmentManager 和 fragmentTransaction;实现fragment的添加，移除，替换（add，remove,replace),记住，当这些事务写完以后要Commit(),保证事务被提交，这样才会生效。 

[java] view plaincopy在CODE上查看代码片派生到我的代码片

[java] view plaincopy在CODE上查看代码片派生到我的代码片下面是一个DEMO：  import android.util.Log;  import android.view.LayoutInflater;  import android.view.View;  import android.view.ViewGroup;  import android.widget.Button;  import android.support.v4.app.FragmentManager;      /**    Fragment的生命周期:  * 第一次启动该fragment:   onCreate --> onCreateView -->onStart --> onResume  *  变得不处于前台的时候：onPause  -->onDestroyView  *  重新回到前台时候：OnCreateView -->onStart --> onResume  * @author yesong  *  */  public class ContentFragment extends Fragment {        private Button mStartButton;        @Override      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          Log.i("yesongyesong", "ContentFragment : onCreate ");      }                             @Override      public View onCreateView(LayoutInflater inflater, ViewGroup container,              Bundle savedInstanceState) {            View view = inflater.inflate(R.layout.content_fragment_layout, null);          mStartButton = (Button) view.findViewById(R.id.start_button);          mStartButton.setOnClickListener(new View.OnClickListener() {              @Override              public void onClick(View v) {                  MainActivity activity = (MainActivity) getActivity();                  activity.enterContentFrament01(mStartButton.getText().toString());                }          });            return view;      }    }  第二个fragment[java] view plaincopy在CODE上查看代码片派生到我的代码片package cn.mmb.fragment.product;    import android.annotation.SuppressLint;  import android.os.Bundle;  import android.support.v4.app.Fragment;  import android.util.Log;  import android.view.LayoutInflater;  import android.view.View;  import android.view.ViewGroup;  import android.widget.Button;  import cn.mmb.fragment.MainActivity;  import cn.mmb.fragment.R;  import cn.mmb.fragment.inter.ViewClickListener;    @SuppressLint("ValidFragment")  public class Content01_Fragment extends Fragment {        private Button mStartButton;        /*      * private ViewClickListener viewClickListener; public      * Content01_Fragment(ViewClickListener clickListener){      * this.viewClickListener = clickListener; }      */        @Override      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);      }      }        @Override      public View onCreateView(LayoutInflater inflater, ViewGroup container,              Bundle savedInstanceState) {            View view = inflater.inflate(R.layout.content_01_fragment_layout, null);          mStartButton = (Button) view.findViewById(R.id.content01_button);          mStartButton.setOnClickListener(new View.OnClickListener() {              @Override              public void onClick(View v) {                  MainActivity activity = (MainActivity) getActivity();                  activity.enterContentFrament02(mStartButton.getText().toString());              }          });  [java] view plaincopy在CODE上查看代码片派生到我的代码片     return view;  [java] view plaincopy在CODE上查看代码片派生到我的代码片}  第三个fragment[java] view plaincopy在CODE上查看代码片派生到我的代码片package cn.mmb.fragment.product;    import android.annotation.SuppressLint;  import android.os.Bundle;  import android.support.v4.app.Fragment;  import android.util.Log;  import android.view.LayoutInflater;  import android.view.View;  import android.view.ViewGroup;  import android.widget.Button;  import cn.mmb.fragment.MainActivity;  import cn.mmb.fragment.R;  import cn.mmb.fragment.inter.ViewClickListener;    @SuppressLint("ValidFragment")  public class Content02_Fragment extends Fragment {        private Button mStartButton;        @Override      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);      }        @Override      public View onCreateView(LayoutInflater inflater, ViewGroup container,              Bundle savedInstanceState) {            View view = inflater.inflate(R.layout.content_02_fragment_layout, null);          mStartButton = (Button) view.findViewById(R.id.no_more_button);          mStartButton.setOnClickListener(new View.OnClickListener() {              @Override              public void onClick(View v) {                                  }          });                    return view;      }    }  Activity使用我们已经写好的fragment[java] view plaincopy在CODE上查看代码片派生到我的代码片package cn.mmb.fragment;    import cn.mmb.fragment.product.ButtomFragment;  import cn.mmb.fragment.product.Content01_Fragment;  import cn.mmb.fragment.product.Content02_Fragment;  import cn.mmb.fragment.product.ContentFragment;  import cn.mmb.fragment.product.TitleBarFragment;  import android.os.Bundle;  import android.support.v4.app.FragmentActivity;  import android.support.v4.app.FragmentManager;  import android.support.v4.app.FragmentTransaction;  import android.view.KeyEvent;  import android.view.View;  import android.widget.FrameLayout;  import android.widget.LinearLayout;    public class MainActivity extends FragmentActivity/* implements ViewClickListener */{        private TitleBarFragment mTitleBarFragment;      private ContentFragment mContentFragment;      private Content01_Fragment mContent01Fragment;      private Content02_Fragment mContent02Fragment;      private ButtomFragment mButtomFragment;      //private FrameLayout mContentLayout;      private LinearLayout mTitleBarLayout;      private LinearLayout mButtomLayout;      private FragmentTransaction fragmentTransaction;      private FragmentManager fragmentManager;      /**      *  to remember  current fragment,      *  if mfragmentIndex == 0 that there is currently a  contentFragmemt      */      private int mFragmentIndex = 0;       /**      *  to remember  last time title bar message      */      private String mLastTitleMessage;        @Override      protected void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.activity_main);            mTitleBarLayout = (LinearLayout) findViewById(R.id.titlebar_layout);          //mContentLayout = (FrameLayout) findViewById(R.id.content_layout);          mButtomLayout = (LinearLayout) findViewById(R.id.buttom_layout);          mTitleBarLayout.setVisibility(View.GONE);            fragmentManager = getSupportFragmentManager();          fragmentTransaction = fragmentManager.beginTransaction();            mContentFragment = new ContentFragment();          mButtomFragment = new ButtomFragment();                       fragmentTransaction.add(R.id.content_layout, mContentFragment,null);           fragmentTransaction.add(R.id.buttom_layout, mButtomFragment,null);                    /*fragmentTransaction.replace(R.id.content_layout, mContentFragment);         fragmentTransaction.replace(R.id.buttom_layout, mButtomFragment);*/          fragmentTransaction.commit();        }         /**        * Before using a callback to control other fragment and some view,       * but now find  a better method : Fragment.this.getActivity();       */      /* @Override       public void buttonClick(View v, String msg) {         switch (v.getId()) {        case R.id.start_button: enterContentFrament01(msg);       break;       case R.id.content01_button: enterContentFrament02(msg); break;       default: break;        }        }*/        /**      * enter the  Third content fragment      * @param msg : the  titleBarMessage      */      public void enterContentFrament02(String msg) {            if (mTitleBarFragment != null) {              mLastTitleMessage = mTitleBarFragment.getTitleMessage();              mTitleBarFragment.setTitleMessage(msg);          }          if (mContent02Fragment == null) {              mContent02Fragment = new Content02_Fragment();          }          fragmentTransaction = fragmentManager.beginTransaction();                    fragmentTransaction.replace(R.id.content_layout, mContent02Fragment);                    //fragmentTransaction.add(R.id.content_layout, mContent02Fragment);          fragmentTransaction.addToBackStack(null);          fragmentTransaction.commit();          mFragmentIndex++;        }        /**      * enter the  second content fragment      * @param msg : the  titleBarMessage      */      public void enterContentFrament01(String msg) {            if (mTitleBarFragment == null) {              mTitleBarFragment = new TitleBarFragment(msg);          }          mLastTitleMessage = mTitleBarFragment.getTitleMessage();          mTitleBarFragment.setTitleMessage(msg);  //set TitleBar message            if (mContent01Fragment == null) {              mContent01Fragment = new Content01_Fragment();          }          mTitleBarLayout.setVisibility(View.VISIBLE);             mButtomLayout.setVisibility(View.GONE);          fragmentTransaction = fragmentManager.beginTransaction();          fragmentTransaction.replace(R.id.titlebar_layout, mTitleBarFragment);          fragmentTransaction.replace(R.id.content_layout, mContent01Fragment);                    /*fragmentTransaction.add(R.id.titlebar_layout, mTitleBarFragment);         fragmentTransaction.add(R.id.content_layout, mContent01Fragment);*/                    fragmentTransaction.addToBackStack(null);          fragmentTransaction.commit();          mFragmentIndex++;        }        @Override      public boolean onKeyUp(int keyCode, KeyEvent event) {            if (keyCode == KeyEvent.KEYCODE_BACK) {              mFragmentIndex--;              if (mFragmentIndex == 0) {                   mButtomLayout.setVisibility(View.VISIBLE);                  mTitleBarLayout.setVisibility(View.GONE);              }          }          if (mTitleBarFragment != null) {              mTitleBarFragment.setTitleMessage(mLastTitleMessage);          }          return super.onKeyUp(keyCode, event);      }    }  运行效果图：            第一个fragment  （白色）                   第2个fragment  （黄色）              第3个fragment（红色）  点击button进入第2个fragment           点击button进入第3个fragment                      下面的的menu也是fragment              上面的titleBar也是一个fragment 以上是多个fragment都在同一个Activity中跳转。

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