Android之Fragment(碎片)

Fragment简介

碎片（Fragment）是一种可以嵌入到活动当中的UI片段，它能让程序更加合理和充分的利用大屏幕的空间。

Fragment的生命周期

它与Activity生命周期的关系：







可以看到Fragment比Activity多了几个额外的生命周期回调方法：

onAttach(Activity)

当Fragment与Activity发生关联时调用。

onCreateView(LayoutInflater, ViewGroup,Bundle)

创建该Fragment的视图

onActivityCreated(Bundle)

当Activity的onCreate方法返回时调用

onDestoryView()

与onCreateView想对应，当该Fragment的视图被移除时调用

onDetach()

与onAttach相对应，当Fragment与Activity关联被取消时调用

注意：除了onCreateView，其他的所有方法如果你重写了，必须调用父类对于该方法的实现，

Fragment的简单用法

步骤：

1、写一个layout,只放一个Button

[code]<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <Button
        android:id="@+id/fragment_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="FragmentTest" />
</LinearLayout>

2,新建一个Fragment类，继承自supportV4 的Fragment

[code]public class FragmentTest extends Fragment {
    private Button mButtonTest;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
         View view=inflater.inflate(R.layout.activity_fragmenttest,null);
        mButtonTest= (Button) view.findViewById(R.id.button);
        mButtonTest.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //点击按钮时会弹出一个Toast
                Toast.makeText(getActivity(), "我点击了这个按钮", Toast.LENGTH_SHORT).show();
            }
        });
        return view;
    }
}

3,然后在activity_main中使用标签在布局中添加碎片

[code]<fragment        class="com.example.administrator.myfragment.fragment.MyFirstFragment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        </fragment>

动态添加Fragment

例子：

状态图

步骤：

1,关于layout。

这个例子里我要添加了3个碎片，所以我写了三个不同layout。以及放fragment的activity_main。

第一个layout(fragmenttest)

[code]<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
   <Button
       android:id="@+id/button"
       android:text="测试按钮"
       android:layout_width="match_parent"
       android:layout_height="wrap_content" />
</LinearLayout>

第二个layout(fragment_second)

[code]<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:background="@mipmap/two"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
   <TextView
       android:id="@+id/textview"
       android:text="我是第二个布局"
       android:layout_width="match_parent"
       android:layout_height="wrap_content" />
</LinearLayout>

第三个layout(fragment_third)

[code]<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
  <ImageView
      android:id="@+id/imageview"
      android:layout_gravity="center"
      android:src="@mipmap/youtou"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" />
</LinearLayout>

activity_mian

[code]<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
  <FrameLayout
      android:id="@+id/frame_container"
      android:layout_width="match_parent"
      android:layout_height="match_parent">
  </FrameLayout>
   <LinearLayout
       android:orientation="horizontal"
       android:gravity="bottom|center"
       android:layout_width="match_parent"
       android:layout_height="match_parent">
       <Button
           android:id="@+id/button1"
           android:text="fragment1"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content" />
       <Button
           android:id="@+id/button2"
           android:text="fragment2"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content" />
       <Button
           android:id="@+id/button3"
           android:text="fragment3"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content" />
   </LinearLayout>
</RelativeLayout>

2,新建三个class继承 Fragment重写onCreateView决定Fragemnt的布局

fragmentTest

[code]public class FragmentTest extends Fragment {
    private Button mButtonTest;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
         View view=inflater.inflate(R.layout.activity_fragmenttest,null);
        mButtonTest= (Button) view.findViewById(R.id.button);
        mButtonTest.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //点击按钮时会弹出一个Toast
                Toast.makeText(getActivity(), "我点击了这个按钮", Toast.LENGTH_SHORT).show();
            }
        });
        return view;
    }
}

fragmentSecond

[code]public class FragmentSecond extends Fragment {

    private TextView mTextView;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view=inflater.inflate(R.layout.fragment_second,null);
        mTextView= (TextView) view.findViewById(R.id.textview);
        return view;
    }
    //修改文本框的内容
    public void setText(String text){
        if(mTextView!=null){
            mTextView.setText(text);
        }
    }
}

fragmentThird

[code]public class FragmentThird extends Fragment {
    private EditText mEditText;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view=inflater.inflate(R.layout.fragment_third,null);
        mEditText= (EditText) view.findViewById(R.id.editText);
        return view;
    }
    //得到输入框文本的内容
    public String getText(){
        String s=null;
        if(mEditText!=null){
            s=mEditText.getText().toString();
        }
        return s;

    }
}

3、在MainActivity中修改代码实现三个按钮的点击事件，通过按钮的点击事件来加载碎片

[code]public class MainActivity extends FragmentActivity implements View.OnClickListener {
    private Button mButton1;
    private Button mButton2;
    private Button mButton3;
    private FragmentTest mFragmentTest;
    private FragmentSecond mFragmentSecond;
    private FragmentThird   mFragmentThird;
    private FragmentManager mFragmentManager;
    private android.support.v4.app.FragmentTransaction transaction;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mButton1= (Button) findViewById(R.id.button1);
        mButton2= (Button) findViewById(R.id.button2);
        mButton3= (Button) findViewById(R.id.button3);
        mButton1.setOnClickListener(this);
        mButton2.setOnClickListener(this);
        mButton3.setOnClickListener(this);

        mFragmentTest=new FragmentTest();
        mFragmentSecond=new FragmentSecond();
        mFragmentThird=new FragmentThird();
        mFragmentManager=getSupportFragmentManager();
        transaction=mFragmentManager.beginTransaction();
        transaction.add(R.id.frame_container,mFragmentTest);
        transaction.add(R.id.frame_container,mFragmentSecond);
        transaction.add(R.id.frame_container,mFragmentThird);
        transaction.hide(mFragmentTest);//隐藏界面
        transaction.hide(mFragmentSecond);
        transaction.commit();
    }

    @Override
    public void onClick(View v) {
      switch (v.getId()){
          case R.id.button1:
              transaction=mFragmentManager.beginTransaction();
              // transaction.replace()把之前的页面删掉重新加载new FragmentTest()在FrameLayout上
             // transaction.replace(R.id.frame_container,new FragmentTest());//frame_container是FrameLayout的id
              transaction.hide(mFragmentSecond);
              transaction.hide(mFragmentThird);
              transaction.show(mFragmentTest);
              transaction.commit();
          break;
          case R.id.button2:
              transaction=mFragmentManager.beginTransaction();
             // transaction.replace(R.id.frame_container,new FragmentSecond());
              String text=mFragmentThird.getText();
              mFragmentSecond.setText(text);
              transaction.hide(mFragmentTest);
              transaction.hide(mFragmentThird);
              transaction.show(mFragmentSecond);
              transaction.commit();

              break;
          case R.id.button3:
              transaction=mFragmentManager.beginTransaction();
              //transaction.replace(R.id.frame_container,new FragmentThird());
              transaction.hide(mFragmentSecond);
              transaction.hide(mFragmentTest);
              transaction.show(mFragmentThird);
              transaction.commit();
              break;
          default:
              break;
      }
    }
}