如何在 Android 中使用 Fragments答案

【问题标题】：How to use Fragments in Android如何在 Android 中使用 Fragments
【发布时间】：2013-04-16 09:39:38
【问题描述】：

编辑 ::: 请参考下面我的回答...

问题:::

我对在 Android 中使用 Fragments 非常陌生，我完全搞砸了。

我只是想构建一个使用片段的简单示例应用程序。我的情况是，我的主要活动中有两个片段。第一个片段有一个编辑文本和一个按钮。第二个片段有一个文本视图。当我在edittext中输入名称并单击按钮时，第二个片段中的textview应该显示在第一个片段的edittext中输入的名称。

我正在使用片段的静态分配（在 XML 中分配片段）。

请参考下面的 XML 文件和代码...

activity_main.XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <fragment
        android:id="@+id/fragment_content_1"
        android:name="com.example.fragmentexample.fragment_fragment_1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >
    </fragment>

    <fragment
        android:id="@+id/fragment_content_2"
        android:name="com.example.fragmentexample.fragment_fragment_2"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >

        <!-- Preview: layout=@layout/fragment_basic -->
    </fragment>

</LinearLayout>

fragment_fragment_1.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" >

    <EditText
        android:id="@+id/edtxtPersonName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/btnSayHi"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Say Hi" />

</LinearLayout>

fragment_fragment_2.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/txtViewResult"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="I will say Hi" />

</LinearLayout>

Java 文件 :::

MainActivity.Java

    public class MainActivity extends Activity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.activity_main, menu);
            return true;
        }

    }

Fragment_1.Java

public class Fragment_1 extends Fragment{

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub      

        View view = inflater.inflate(R.layout.fragment_fragment_1, container, false);

        final EditText edtxtPersonName_Fragment = (EditText) view.findViewById(R.id.edtxtPersonName);
        Button btnSayHi_Fragment = (Button) view.findViewById(R.id.btnSayHi);

        btnSayHi_Fragment.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                String name = edtxtPersonName_Fragment.getText().toString();

                FragmentManager fm = getFragmentManager();
                Fragment_2 f2 = (Fragment_2) fm.findFragmentById(R.id.fragment_content_2);

                if(f2 != null && f2.isInLayout())
                {
                    f2.setName(name);
                }

                Activity activity = getActivity();

                if(activity != null)
                {
                    Toast.makeText(activity, "Say&ing Hi in Progress...", Toast.LENGTH_LONG).show();
                }
            }
        });

        return view;


    }

}

Fragment_2.Java

public class Fragment_2 extends Fragment{

    View view;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub

        view = inflater.inflate(R.layout.fragment_fragment_2, container, false);        
        return view;
    }

    public void setName(String name)
    {
        TextView txtName = (TextView) view.findViewById(R.id.txtViewResult);
        txtName.setText("Hi " + name);
    }

}

当我运行应用程序时，有很多异常.. 这是 logcat 跟踪..

04-16 15:06:48.781: E/AndroidRuntime(420): FATAL EXCEPTION: main
04-16 15:06:48.781: E/AndroidRuntime(420): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fragmentexample/com.example.fragmentexample.MainActivity}: android.view.InflateException: Binary XML file line #5: Error inflating class fragment
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1815)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.ActivityThread.access$500(ActivityThread.java:122)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.os.Looper.loop(Looper.java:132)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.ActivityThread.main(ActivityThread.java:4123)
04-16 15:06:48.781: E/AndroidRuntime(420):  at java.lang.reflect.Method.invokeNative(Native Method)
04-16 15:06:48.781: E/AndroidRuntime(420):  at java.lang.reflect.Method.invoke(Method.java:491)
04-16 15:06:48.781: E/AndroidRuntime(420):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
04-16 15:06:48.781: E/AndroidRuntime(420):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
04-16 15:06:48.781: E/AndroidRuntime(420):  at dalvik.system.NativeStart.main(Native Method)
04-16 15:06:48.781: E/AndroidRuntime(420): Caused by: android.view.InflateException: Binary XML file line #5: Error inflating class fragment
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:688)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.view.LayoutInflater.rInflate(LayoutInflater.java:724)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.view.LayoutInflater.inflate(LayoutInflater.java:479)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.view.LayoutInflater.inflate(LayoutInflater.java:391)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.view.LayoutInflater.inflate(LayoutInflater.java:347)
04-16 15:06:48.781: E/AndroidRuntime(420):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:223)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.Activity.setContentView(Activity.java:1786)
04-16 15:06:48.781: E/AndroidRuntime(420):  at com.example.fragmentexample.MainActivity.onCreate(MainActivity.java:12)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.Activity.performCreate(Activity.java:4397)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1779)
04-16 15:06:48.781: E/AndroidRuntime(420):  ... 11 more
04-16 15:06:48.781: E/AndroidRuntime(420): Caused by: android.app.Fragment$InstantiationException: Unable to instantiate fragment com.example.fragmentexample.fragment_fragment_1: make sure class name exists, is public, and has an empty constructor that is public
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.Fragment.instantiate(Fragment.java:567)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.Fragment.instantiate(Fragment.java:535)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.Activity.onCreateView(Activity.java:4168)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:664)
04-16 15:06:48.781: E/AndroidRuntime(420):  ... 21 more
04-16 15:06:48.781: E/AndroidRuntime(420): Caused by: java.lang.ClassNotFoundException: com.example.fragmentexample.fragment_fragment_1 in loader dalvik.system.PathClassLoader[/data/app/com.example.fragmentexample-1.apk]
04-16 15:06:48.781: E/AndroidRuntime(420):  at dalvik.system.PathClassLoader.findClass(PathClassLoader.java:251)
04-16 15:06:48.781: E/AndroidRuntime(420):  at java.lang.ClassLoader.loadClass(ClassLoader.java:540)
04-16 15:06:48.781: E/AndroidRuntime(420):  at java.lang.ClassLoader.loadClass(ClassLoader.java:500)
04-16 15:06:48.781: E/AndroidRuntime(420):  at android.app.Fragment.instantiate(Fragment.java:557)
04-16 15:06:48.781: E/AndroidRuntime(420):  ... 24 more

我已经看到了有关如何执行此操作的示例，但无法弄清楚。请指出我做错的地区，也请张贴正确的做法。

非常感谢您的宝贵时间...

编辑 :::

我已更改 MainActivity.java 以扩展 FragmentActivity 而不是 Activity，还更改了 activity_main.xml 中的 android:name 值以指向 Java 文件而不是片段...

我得到以下异常 :::

04-16 15:29:43.821: E/AndroidRuntime(563): FATAL EXCEPTION: main
04-16 15:29:43.821: E/AndroidRuntime(563): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fragmentexample/com.example.fragmentexample.MainActivity}: android.view.InflateException: Binary XML file line #5: Error inflating class fragment
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1815)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.ActivityThread.access$500(ActivityThread.java:122)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.os.Looper.loop(Looper.java:132)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.ActivityThread.main(ActivityThread.java:4123)
04-16 15:29:43.821: E/AndroidRuntime(563):  at java.lang.reflect.Method.invokeNative(Native Method)
04-16 15:29:43.821: E/AndroidRuntime(563):  at java.lang.reflect.Method.invoke(Method.java:491)
04-16 15:29:43.821: E/AndroidRuntime(563):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
04-16 15:29:43.821: E/AndroidRuntime(563):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
04-16 15:29:43.821: E/AndroidRuntime(563):  at dalvik.system.NativeStart.main(Native Method)
04-16 15:29:43.821: E/AndroidRuntime(563): Caused by: android.view.InflateException: Binary XML file line #5: Error inflating class fragment
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:688)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.view.LayoutInflater.rInflate(LayoutInflater.java:724)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.view.LayoutInflater.inflate(LayoutInflater.java:479)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.view.LayoutInflater.inflate(LayoutInflater.java:391)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.view.LayoutInflater.inflate(LayoutInflater.java:347)
04-16 15:29:43.821: E/AndroidRuntime(563):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:223)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.Activity.setContentView(Activity.java:1786)
04-16 15:29:43.821: E/AndroidRuntime(563):  at com.example.fragmentexample.MainActivity.onCreate(MainActivity.java:13)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.Activity.performCreate(Activity.java:4397)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1779)
04-16 15:29:43.821: E/AndroidRuntime(563):  ... 11 more
04-16 15:29:43.821: E/AndroidRuntime(563): Caused by: java.lang.ClassCastException: com.example.fragmentexample.Fragment_1 cannot be cast to android.support.v4.app.Fragment
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.support.v4.app.Fragment.instantiate(Fragment.java:394)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.support.v4.app.Fragment.instantiate(Fragment.java:369)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:272)
04-16 15:29:43.821: E/AndroidRuntime(563):  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:660)
04-16 15:29:43.821: E/AndroidRuntime(563):  ... 21 more

这里是activity_main.xml修改后的XML文件

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <fragment
        android:id="@+id/fragment_content_1"
        android:name="com.example.fragmentexample.Fragment_1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >
    </fragment>

    <fragment
        android:id="@+id/fragment_content_2"
        android:name="com.example.fragmentexample.Fragment_2"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >

        <!-- Preview: layout=@layout/fragment_basic -->
    </fragment>

</LinearLayout>

【问题讨论】：

标签： android android-fragments

【解决方案1】：

Okie...终于找到了解决方案。可能变化不大。

查看下面的代码...

activity_main.XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <fragment
        android:id="@+id/fragment_content_1"
        android:name="com.example.fragmentexample.Fragment_1"
        android:layout_width="0dip"
        android:layout_weight="0.50"
        android:layout_height="fill_parent" >
    </fragment>

    <fragment
        android:id="@+id/fragment_content_2"
        android:name="com.example.fragmentexample.Fragment_2"
        android:layout_width="0dip"
        android:layout_weight="0.50"
        android:layout_height="fill_parent" >

        <!-- Preview: layout=@layout/fragment_basic -->
    </fragment>

</LinearLayout>

fragment_fragment_1 和 fragment_fragment_2 的布局保持不变。

Fragment_1.Java

public class Fragment_1 extends Fragment{

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            // TODO Auto-generated method stub      

            View view = inflater.inflate(R.layout.fragment_fragment_1, container, false);

            final EditText edtxtPersonName_Fragment = (EditText) view.findViewById(R.id.edtxtPersonName);
            Button btnSayHi_Fragment = (Button) view.findViewById(R.id.btnSayHi);

            btnSayHi_Fragment.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub

                    String name = edtxtPersonName_Fragment.getText().toString();

                    FragmentManager fm = getFragmentManager();
                    Fragment_2 f2 = (Fragment_2) fm.findFragmentById(R.id.fragment_content_2);

                    if(f2 != null && f2.isInLayout())
                    {
                        f2.setName(name);
                    }

                    Activity activity = getActivity();

                    if(activity != null)
                    {
                        Toast.makeText(activity, "Say&ing Hi in Progress...", Toast.LENGTH_LONG).show();
                    }
                }
            });

            return view;


        }

    }

Fragment_2.Java

public class Fragment_2 extends Fragment{

    View view;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub

        view = inflater.inflate(R.layout.fragment_fragment_2, container, false);        
        return view;
    }

    public void setName(String name)
    {
        TextView txtName = (TextView) view.findViewById(R.id.txtViewResult);
        txtName.setText("Hi " + name);
    }

}

这是屏幕截图...

【讨论】：

但是元素fragment不是empty tag吗？另外我想知道它在您的情况下是如何工作的，我只是复制粘贴了您的整个代码，但仍然出现这些错误。
我对 Fragment 的定义有点困惑？即使从主站点developer.android.com/guide/components/fragments.htmlreading阅读，我对 Fragment 也一无所知，您能否以非常简单的方式定义 Fragment 是什么？

【解决方案2】：

您需要向 Fragments 添加一个空的公共构造函数，就像堆栈跟踪中所说的那样：

public class Fragment_2 extends Fragment{

    public Frament_2() {
        //BLAH!
    }

    // The rest of your code

}

【讨论】：

我添加了构造函数。异常没有变化...我得到相同的异常来添加构造函数
我明白了。。我刚刚注意到一个问题，你不需要扩展 FragmentActivity 来显示片段吗？
改成FragmentActivity，更新问题，请看
FragmentActivity 只有在我们使用片段支持库时才会被扩展。否则，扩展活动就可以了。刚学会这个！！
嗯...这是有道理的。我一直使用支持库，所以这就是我不知道的原因，我猜！不过，很高兴知道您找到了解决方案。

【解决方案3】：

这是两个 Fragment 之间通信的经典案例。
但让我们先介绍一些更基本的东西。

碎片骨架

第一个片段

编辑文本
按钮

public class FirstFragment extends Fragment{

      private EditText editext;
      private Button button;

      public static FirstFragment getInstance(){  
           return new FirstFragment();
      }

      public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle bundle){
           View view = inflater.inflate(R.Layout.fragment1,parent,false);
           editext = (EditText)view.findViewById(R.id.editText)
           button = (Button)view.findViewById(R.id.button)
           return view;               

      }

}

第二个片段

文本视图

public class SecondFragment extends Fragment{

      private TextView textView;

      public static SecondFragment getInstance(){  
           return new SecondFragment();
      }

      public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle bundle){
           View view = inflater.inflate(R.Layout.fragment2,parent,false);
           textView = (TextView)view.findViewById(R.id.editText)
           return view;               

      }

      public void showMessage(String msg)
      {
           textView.setText(msg)
      }

}

如何创建片段实例

FirstFragment fragmne1 = FirstFragment.getInstance();
SecondFragment fragmne1 = SecondFragment.getInstance();

如何在 Activity 中添加它们？

getSupportFragmentManager()
         .beginTransaction()
         .add(R.id.placeholder1,fragment1,"TAG1")
         .add(R.id.placeholder2,fragment2,"TAG2")
         .commit();

现在是交流部分

创建界面

public interface FragmentListener{
     public void buttonClicked();
}

在Activity中实现这个接口并覆盖方法

public MyActivity extends AppcompatActivity implements MyFragmentListener{

     @Override
     public void buttonClicked(){
          fragment2.showMessage(String msg);
     }

}

从 Fragment 发送数据

在 FirstFragment 中初始化监听器
按钮点击时调用接口方法。

FirstFragment的最终结构

public class FirstFragment extends Fragment{

      private EditText editext;
      private Button button;
      private MyFragmentListener listener;

      public static FirstFragment getInstance(){  
           return new FirstFragment();
      }

      public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle bundle){
           View view = inflater.inflate(R.Layout.fragment1,parent,false);
           editext = (EditText)view.findViewById(R.id.editText)
           button = (Button)view.findViewById(R.id.button)

           // button click method 
           listener.buttonClicked(editText.getText().toString());

           return view;               

      }

      @Override 
      public void onAttach(Context context){
           listener = (MyFragmentListener)context;
      }

}

【讨论】：

【解决方案4】：

请按如下方式编辑您的activity_main.XML。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent" >

<fragment
    android:id="@+id/fragment_content_1"
    android:name="com.example.fragmentexample.fragment_fragment_1"
    class="com.example.fragmentexample.fragment_fragment_1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >
</fragment>

<fragment
    android:id="@+id/fragment_content_2"
    android:name="com.example.fragmentexample.fragment_fragment_2"
    class="com.example.fragmentexample.fragment_fragment_2"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <!-- Preview: layout=@layout/fragment_basic -->
</fragment>
</LinearLayout>

【讨论】：