两个简单实例，学会使用fragment

实例一，简单Fragment

MainActivity

package com.example.demo;import android.content.Intent;import android.os.Bundle;import android.support.v4.app.FragmentActivity;import android.support.v4.app.FragmentTransaction;import android.view.View;public class MainActivity extends FragmentActivity {public static String temp="weesdf";public static String getTemp() {return temp;}public static void setTemp(String temp) {MainActivity.temp = temp;}public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//Intent intent=new Intent(MainActivity.this,);FragmentTransaction ft = getSupportFragmentManager().beginTransaction();FirstFragment first = new FirstFragment();                //如果用add()的话会出现不完全覆盖效果ft.replace(R.id.container, first);ft.commit();}//切换到第二个fragmentpublic void onClick_btn(View v){FragmentTransaction ft = getSupportFragmentManager().beginTransaction();SecondFragment second = new SecondFragment();ft.replace(R.id.container, second);ft.commit();}}

Activity_Second

package com.example.demo;import android.os.Bundle;import android.support.v4.app.FragmentActivity;import android.support.v4.app.FragmentTransaction;public class Activity_Second extends FragmentActivity {public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_second);}}

FirstFragment

package com.example.demo;import android.content.Intent;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.Button;public class FirstFragment extends Fragment {public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {View view = inflater.inflate(R.layout.fragment_first, container, false);Button bt_first = (Button) view.findViewById(R.id.bt_first);bt_first.setText(MainActivity.temp);bt_first.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent intent=new Intent(getActivity(),Activity_Second.class);startActivity(intent);}});return view;}}

SecondFragment

package com.example.demo;import android.os.Bundle;import android.support.v4.app.Fragment;import android.support.v4.app.FragmentTransaction;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.view.View.OnClickListener;import android.widget.Button;public class SecondFragment extends Fragment {public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {View view = inflater.inflate(R.layout.fragment_second, container, false);Button bt_second = (Button) view.findViewById(R.id.bt_second);bt_second.setOnClickListener(new OnClickListener() {public void onClick(View v) {FragmentTransaction ft = getFragmentManager().beginTransaction();ft.setCustomAnimations(R.animator.move_in, R.animator.move_out);FirstFragment first = new FirstFragment();ft.replace(R.id.container, first);ft.commit();}});return view;}}

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="fill_parent"    android:layout_height="match_parent"    android:orientation="vertical" >     <Button        android:id="@+id/btn"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:onClick="onClick_btn"        android:text="@string/app_name" />     <RelativeLayout        android:id="@+id/container"        android:layout_width="fill_parent"        android:layout_height="200dp" /></LinearLayout>

fragmentfirst.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="match_parent"    android:orientation="vertical"    android:background="#cba" >    <TextView        android:id="@+id/tv_first"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_horizontal"        android:text="这是第一个Fragment"        android:textAppearance="?android:attr/textAppearanceLarge" />    <Button        android:id="@+id/bt_first"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_horizontal"        android:text="点我进入下一个" /></LinearLayout>

fragmentsecond.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="match_parent"    android:background="#abc"    android:orientation="vertical" >    <TextView        android:id="@+id/tv_second"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_horizontal"        android:text="这是第二个Fragment"        android:textAppearance="?android:attr/textAppearanceLarge" />    <Button        android:id="@+id/bt_second"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_horizontal"        android:text="点我回到第一个" /></LinearLayout>

实例二， Fragment与activity通信

首先,如果你想在android3.0及以下版本使用fragment,你必须引用android-support-v4.jar这个包

然后你写的activity不能再继承自Activity类了,而是要继承android.support.v4.app.FragmentActivity,一些其他的父类也有相应的变化.

由于在android的实现机制中fragment和activity会被分别实例化为两个不相干的对象,他们之间的联系由activity的一个成员对象fragmentmanager来维护.fragment实例化后会到activity中的fragmentmanager去注册一下,这个动作封装在fragment对象的onAttach中,所以你可以在fragment中声明一些回调接口,当fragment调用onAttach时,将这些回调接口实例化,这样fragment就能调用各个activity的成员函数了,当然activity必须implements这些接口,否则会包classcasterror

fragment和activity的回调机制又是OOP的一次完美演绎!

下面通过一个例子来说明：

 

我把Activity的UI分为两个部分，左边和右边，左边用来放置点击的按钮(LeftFragment),右边用来放置对应点击后显示的信息(RightFragment).

Activity的布局layout文件：main.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="horizontal" >        <LinearLayout         android:id="@+id/left_layout"        android:layout_width="wrap_content"        android:layout_height="fill_parent"        android:layout_weight="1"        android:orientation="vertical" >     </LinearLayout>        <LinearLayout         android:id="@+id/right_layout"        android:layout_width="wrap_content"        android:layout_height="fill_parent"        android:layout_weight="10"        android:orientation="vertical" >     </LinearLayout>    </LinearLayout>

LeftFragment的布局layout：leftfragment.xml

<?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="vertical" >        <Button         android:id="@+id/first_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/first_button" />        <Button         android:id="@+id/second_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/second_button" />        <Button         android:id="@+id/third_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/third_button" />    </LinearLayout>

RightFragment的布局layout:rightfragment.xml

<?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="vertical" >        <TextView         android:id="@+id/right_show_message"        android:layout_width="fill_parent"        android:layout_height="fill_parent"        android:background="@android:color/holo_orange_dark"        android:textColor="@android:color/white" />    </LinearLayout>

以上是两个fragment和一个Activity的布局文件，下面来看他们的java文件

Activity:

public class FirstActivity extends Activity implements MyListener {     /**      * 实现MyListener,当LeftFragment中点击第一页的时候，让RightFragment显示第一页信息,同理当点击第二页的时候，RightFragment显示第二页信息      *       * @param index      *            显示的页数      */    public void showMessage(int index)     {         if (1 == index)             showMessageView.setText(R.string.first_page);         if (2 == index)             showMessageView.setText(R.string.second_page);         if (3 == index)             showMessageView.setText(R.string.third_page);     }        /** 得到RightFragment中显示信息的控件 */    private TextView showMessageView;        /** Called when the activity is first created. */    @Override     public void onCreate(Bundle savedInstanceState)     {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);         System.out.println("Activity--->onCreate");            FragmentManager manager = getFragmentManager();         FragmentTransaction transaction = manager.beginTransaction();         // 动态增加Fragment         RightFragment rightFragment = new RightFragment();         LeftFragment leftFragment = new LeftFragment();         transaction.add(R.id.left_layout, leftFragment, "leftfragment");         transaction.add(R.id.right_layout, rightFragment, "rightfragment");         transaction.commit();        }        @Override     protected void onResume()     {         super.onResume();         System.out.println("Activity--->onResume"); //注意：findview放到这里        showMessageView = (TextView) findViewById(R.id.right_show_message);     } }

LeftFragment:

public class LeftFragment extends Fragment {     /** Acitivity要实现这个接口，这样Fragment和Activity就可以共享事件触发的资源了 */    public interface MyListener     {         public void showMessage(int index);     }        private MyListener myListener;     private Button firstButton;     private Button secondButton;     private Button thirdButton;        /** Fragment第一次附属于Activity时调用,在onCreate之前调用 */    @Override     public void onAttach(Activity activity)     {         super.onAttach(activity);         System.out.println("LeftFragment--->onAttach");            myListener = (MyListener) activity;     }        @Override     public void onCreate(Bundle savedInstanceState)     {         super.onCreate(savedInstanceState);         System.out.println("LeftFragment--->onCreate");     }        @Override     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)     {         System.out.println("LeftFragment--->onCreateView");         return inflater.inflate(R.layout.leftfragment, container, false);     }        @Override     public void onResume()     {         super.onResume();         System.out.println("LeftFragment--->onResume");            firstButton = (Button) getActivity().findViewById(R.id.first_button);         secondButton = (Button) getActivity().findViewById(R.id.second_button);         thirdButton = (Button) getActivity().findViewById(R.id.third_button);            MyButtonClickListener clickListener = new MyButtonClickListener();         firstButton.setOnClickListener(clickListener);         secondButton.setOnClickListener(clickListener);         thirdButton.setOnClickListener(clickListener);     }        /** 按钮的监听器 */    class MyButtonClickListener implements OnClickListener     {         public void onClick(View v)         {             Button button = (Button) v;             if (button == firstButton)                 myListener.showMessage(1);             if (button == secondButton)                 myListener.showMessage(2);             if (button == thirdButton)                 myListener.showMessage(3);         }     } }

RightFragment

public class RightFragment extends Fragment {     @Override     public void onCreate(Bundle savedInstanceState)     {         System.out.println("RightFragment--->onCreate");         super.onCreate(savedInstanceState);     }        @Override     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)     {         System.out.println("RightFragment--->onCreateView");         return inflater.inflate(R.layout.rightfragment, container, false);     } }

注意，Fragment的生命周期和Activity生命周期之间的关系。在Activity里动态生成Fragment，首先是Activity调用onCreate()方法，但是这时候还没有加载到Fragment里的组件，当Fragment调用其onCreateView()方法后，Activity才能得到Fragment中的组件

这里最关键的就是Fragment要有一个接口和这个接口的引用，而这个接口需要Activity去实现它。当Fragment调用onAttach(Activity acitivity)方法的时候，将这个activity传递给这个接口引用，这样，就可以和Activity进行交互了.