"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

二setArgumentsBundle

二描述Fragment的生命周期
一生命周期图

二需求

三代码

三Fragment的replace和add方法的区别
两者比较和注意点

四Fragment如何实现类似Activity的压栈和出栈效果

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

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

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)



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

@Override
public 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

@Override
public 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;
}
}
}

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.

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