"Fragment"-Android面试必问"精华技能点"汇总

Fragment技能点汇总总结:
目录:

一.Fragment跟Activity如何传值?

一.getActivity()

• 1.从Fragment获取Ativity的信息
• 2.就可以调用Ativity的方法了

二.setArguments(Bundle)

• 在Ativity获取Fragment的实例和方法

• 过程和代码如下：

  • 1.获取管理者

    FragmentManager fragmentManager = getFragmentManager();

  • 2.找到fragment

    Fragment fragment = fragmentManager.findFragmentByTag(tag);Fragment fragment = fragmentManager.findFragmentById(id);

  • 3.一般直接管理对象.获取事物(替换布局,frgmentXX).提交.

• 可调用fragment的setArguments(bundle)把数据绑定到Fragment中.
• 为什么官方推荐 Fragment.setArguments(Bundle bundle)这种方式来传递参数，而不推荐通过构造方法直接来传递参数呢？ 请看以下两个例子：

案例一：通过fragment构造传给Activity

public class FramentTestActivity extends ActionBarActivity {  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    if (savedInstanceState == null) {      getSupportFragmentManager().beginTransaction()          .add(R.id.container, new TestFragment("param")).commit();    }  }  public static class TestFragment extends Fragment {    private String mArg = "non-param";    public TestFragment() {      Log.i("INFO", "TestFragment non-parameter constructor");    }    public TestFragment(String arg){      mArg = arg;      Log.i("INFO", "TestFragment construct with parameter");    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,        Bundle savedInstanceState) {      View rootView = inflater.inflate(R.layout.fragment_main, container,          false);      TextView tv = (TextView) rootView.findViewById(R.id.tv);      tv.setText(mArg);      return rootView;    }  }}

结果: 能正常显示
当横屏后:得到的值为null

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案例二:换成setArguments(bundle)传递值

public class FramentTest2Activity extends ActionBarActivity {        @Override        protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);             setContentView(R.layout. activity_main);  if (savedInstanceState == null) {        getSupportFragmentManager().beginTransaction()         .add(R.id. container, TestFragment.newInstance("param")).commit();             }       }        public static class TestFragment extends Fragment {  private static final String ARG = "arg";  public TestFragment() {        Log. i("INFO", "TestFragment non-parameter constructor" );             }  public static Fragment newInstance(String arg){        TestFragment fragment = new TestFragment();        Bundle bundle = new Bundle();        bundle.putString( ARG, arg);        fragment.setArguments(bundle);         return fragment;             }  @Override  public View onCreateView(LayoutInflater inflater, ViewGroup container,               Bundle savedInstanceState) {        View rootView = inflater.inflate(R.layout. fragment_main, container,          false);        TextView tv = (TextView) rootView.findViewById(R.id. tv);        tv.setText(getArguments().getString( ARG));         return rootView;             }       }}

不论横屏还是竖屏都会得到值

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二.描述Fragment的生命周期

一.生命周期图:

二.需求

• 1.屏幕分左右边,左边2/5是点击列表,右边是:上输入框,下文本框
• 2.最后一个内容fragment,多了个点击按钮.并能获取Activity里的输入框信息.
• 3.效果图如下图1,2,3
  

三.代码:

布局:
activity_main.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="horizontal"    >    <LinearLayout        android:layout_width="0dp"        android:layout_height="match_parent"        android:layout_weight="2"        android:background="#22ff0000"        android:orientation="vertical">        <Button            android:id="@+id/bt_news"            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:text="新闻"/>        <Button            android:id="@+id/bt_fun"            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:text="娱乐"/>        <TextView            android:id="@+id/tv_sport"            android:layout_width="match_parent"            android:layout_height="40dp"            android:background="#22000000"            android:gravity="center"            android:text="体育"/>    </LinearLayout><LinearLayout    android:orientation="vertical"    android:layout_width="0dp"    android:layout_weight="5"    android:layout_height="match_parent">    <EditText        android:id="@+id/et_info"        android:layout_width="match_parent"        android:hint="请输入内容"        android:layout_height="wrap_content"/>    <FrameLayout        android:id="@+id/fl_content"        android:background="#2200ff00"        android:layout_width="match_parent"        android:layout_height="match_parent">    </FrameLayout></LinearLayout></LinearLayout>

fragment_fun.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:layout_width="match_parent"              android:orientation="vertical"              android:layout_height="match_parent">    <TextView        android:background="#33ff00f7"        android:gravity="center"        android:text="我是娱乐"        android:layout_width="match_parent"        android:layout_height="match_parent"/></LinearLayout>

fragment_news.xml

android:background="#330000ff"android:text="我是新闻"

fragment_sport.xml

<Button    android:onClick="getInfo"    android:id="@+id/bt_getInfo"    android:text="获取输入框内容"    android:layout_width="match_parent"    android:layout_height="wrap_content"/><Button    android:onClick="goFun"    android:id="@+id/bt_goFun"    android:text="跳到Fun板块"    android:layout_width="match_parent"    android:layout_height="wrap_content"/><TextView    android:gravity="center"    android:text="我是运动"    android:layout_width="match_parent"    android:layout_height="match_parent"/>

Java代码:
(分类写)

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Fragment_fun.java

public class Fragment_fun extends Fragment {    //1.固定    @Override    public void onAttach(Context context) {        Log.d("abce", "onAttach");        super.onAttach(context);    }    //2.创建    @Override    public void onCreate(Bundle savedInstanceState) {        Log.d("abce", "onCreate");        super.onCreate(savedInstanceState);    }    //3.创建View    @Nullable    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {        Log.d("abce", "onCreateView");        //填充布局进来        return inflater.inflate(R.layout.fragment_fun,null);    }    //4.创建活动界面    @Override    public void onActivityCreated(Bundle savedInstanceState) {        Log.d("abce", "onActivityCreated");        super.onActivityCreated(savedInstanceState);    }    @Override    public void onDestroyView() {        Log.d("abce", "onDestroyView");        super.onDestroyView();    }    @Override    public void onDestroy() {        Log.d("abce", "onDestroy");        super.onDestroy();    }    @Override    public void onDetach() {        Log.d("abce", "onDetach");        super.onDetach();    }}

Fragment_news.java

@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {    Log.d("abce", "onCreateView");    //填充布局    return inflater.inflate(R.layout.fragment_news,null);}

Fragment_sport.java

@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {    Log.d("abce", "onCreateView");    View view =inflater.inflate(R.layout.fragment_sport,null);    mBt_getInfo = (Button) view.findViewById(R.id.bt_getInfo);    mBt_getInfo.setOnClickListener(new View.OnClickListener() {        @Override        public void onClick(View v) {            //通过getActivity()方法获取到绑定的Activity对象            EditText et = (EditText) getActivity().findViewById(R.id.et_info);            String str = et.getText().toString().trim();            if (TextUtils.isEmpty(str)) {                Toast.makeText(getActivity(), "null", Toast.LENGTH_SHORT).show();                return;            }            Toast.makeText(getActivity(),"获取到的信息是"+str,Toast.LENGTH_SHORT).show();        }    });    Button goA = (Button) view.findViewById(R.id.bt_goFun);    goA.setOnClickListener(new View.OnClickListener() {        @Override        public void onClick(View v) {            getFragmentManager().beginTransaction().replace(R.id.fl_content, new Fragment_fun()).commit();        }    });    return view;}

MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener {    private Button mBt_news;    private Button mBt_fun;    private TextView mTv_sport;    private FragmentTransaction mFt;    private FragmentManager mFm;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        init();        initView();    }    private void init() {        // 获取管理对象        mFm = getFragmentManager();        // 获取事物        mFt = mFm.beginTransaction();        // 开始的时候马上替换,帧布局先放new模块;        mFt.replace(R.id.fl_content, new Fragment_news());        // 提交        mFt.commit();    }    private void initView() {        mBt_news = (Button) findViewById(R.id.bt_news);        mBt_fun = (Button) findViewById(R.id.bt_fun);        mTv_sport = (TextView) findViewById(R.id.tv_sport);        mBt_news.setOnClickListener(this);        mBt_fun.setOnClickListener(this);        mTv_sport.setOnClickListener(this);    }    /**     * 各个板块的点击事件: 每点击一个,创建一个: 1.管理 2.事务 3.事务替换内容 4.提交     */    @Override    public void onClick(View v) {        switch (v.getId()) {        case R.id.bt_news:            getFragmentManager().beginTransaction().replace(R.id.fl_content, new Fragment_news()).commit();            break;        case R.id.bt_fun:            getFragmentManager().beginTransaction().replace(R.id.fl_content, new Fragment_fun()).commit();            break;        case R.id.tv_sport:            getFragmentManager().beginTransaction().replace(R.id.fl_content, new Fragment_sport()).commit();            break;        }    }}

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三.Fragment的replace和add方法的区别

• 严格意义上讲不是fragment的方法,而是管理者的方法
• 常用:比如RadioGroup切换Fragment(每个Fragment都是一个独立的功能模块)

两者比较和注意点:

• 1.add的时候可以把Fragment 一层层添加到FrameLayout上面,而replace是删掉其他并替换
• 2.一个FrameLayout只能添加一个Fragment种类,多次添加会报异常,replace则随便替换
  
  • 替换(上一个fragment会->destroyView和destroy,新的Fragmetnon:三个Create(crete+view+activity)->onStart->onResume)
• 3.因FrameLayout容器对每个Fragment只能添加一次,所以到达到效果可用fragment的hide和show方法结合.
  

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四.Fragment如何实现类似Activity的压栈和出栈效果?

• 内部维持的是双向链表结构
• 该结构可记录我们每次的add和replace我们的Fragment;
• 当我们点击back按钮会自动帮我们实现退栈按钮