Navigation简单使用

Google 2018 I/O大会上,谷歌隆重推出一个新的架构组件:Navigation，它提供了多Fragment之间的转场，栈管理，帮助你更轻松的使用Fragment；

简单使用：

下面的例子采用androidx+java的形式书写：

build.gradle

dependencies {
    implementation "androidx.navigation:navigation-fragment:2.0.0"
    implementation "androidx.navigation:navigation-ui:2.0.0"
}

2.新建两个fragment
fragment_first.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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=".FirstFragment">
 
    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_marginTop="100dp"
        android:layout_gravity="center_horizontal"
        android:text="我是第一个Fragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
 
    <Button
        android:textAllCaps="false"
        android:id="@+id/btn_next"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="跳转到第二个Fragment" /> 
</FrameLayout>

fragment_second.xml

<FrameLayout 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"
    android:orientation="vertical"
    tools:context=".SecondFragment">
 
    <!-- TODO: Update blank fragment layout -->
 
    <TextView
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="100dp"
        android:text="我是第二个Fragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
 
    <Button
        android:layout_gravity="center"
        android:id="@+id/btn_back"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="返回" />
</FrameLayout>

创建导航视图文件
在res目录下新建navigation文件夹，然后新建一个navigation资源文件nav_fragment.xml,

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    app:startDestination="@id/firstFragment">
 
    <fragment
        android:id="@+id/firstFragment"
        android:name="com.example.jatpack.navigation.FirstFragment"
        android:label="fragment_first"
        tools:layout="@layout/fragment_first" >
        <action
            android:id="@+id/action_firstFragment_to_secondFragment"
            app:destination="@id/secondFragment" />
    </fragment>
    <fragment
        android:id="@+id/secondFragment"
        android:name="com.example.jatpack.navigation.SecondFragment"
        android:label="fragment_second"
        tools:layout="@layout/fragment_second" >
    </fragment>
</navigation>

app:startDestination：默认的起始位置

在activity布局中添加fragment组件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
 
   <fragment
       android:name="androidx.navigation.fragment.NavHostFragment"
       android:id="@+id/fragment"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       app:defaultNavHost="true"
       app:navGraph="@navigation/nav_fragment" />
 
</RelativeLayout>

android:name：值必须是androidx.navigation.fragment.NavHostFragment，声明这是一个NavHostFragment
app:navGraph：存放的是第3步建好导航的资源文件
app:defaultNavHost="true"：与系统的返回按钮相关联

MainActivity.java

public class MainActivity extends AppCompatActivity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
 
    @Override
    public boolean onSupportNavigateUp() {
        Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.fragment);
        return NavHostFragment.findNavController(fragment).navigateUp();
    }
}

重写onSupportNavigateUp（）方法，目的是将back事件委托出去。若栈中有两个以上Fragment，点击back键就会返回到上一个Fragment。

在Fragment中设置相应的跳转事件

public class FirstFragment extends Fragment {
 
    public FirstFragment() {
        // Required empty public constructor
    }
 
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_first, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Button btnNext = view.findViewById(R.id.btn_next);
        btnNext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Navigation.findNavController(v).navigate(R.id.action_firstFragment_to_secondFragment);
            }
        });
    }
}

public class SecondFragment extends Fragment {
 
    public SecondFragment() {
        // Required empty public constructor
    }
 
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_second, container, false);
    }
 
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Button btnBack = view.findViewById(R.id.btn_back);
        btnBack.setOnClickListener(new View.OnClickListener(){
 
            @Override
            public void onClick(View v) {
                Navigation.findNavController(v).navigateUp();
            }
        });
    }
}

跳转到activity

修改nav_fragment.xml

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    app:startDestination="@id/firstFragment">
 
    <fragment
        android:id="@+id/firstFragment"
        android:name="com.example.jatpack.navigation.FirstFragment"
        android:label="fragment_first"
        tools:layout="@layout/fragment_first" >
        <action
            android:id="@+id/action_firstFragment_to_secondFragment"
            app:destination="@id/secondFragment" />
       <action
            android:id="@+id/action_firstFragment_to_activity"
            app:destination="@id/activity" />
    </fragment>
    <fragment
        android:id="@+id/secondFragment"
        android:name="com.example.jatpack.navigation.SecondFragment"
        android:label="fragment_second"
        tools:layout="@layout/fragment_second" >
    </fragment>
   <activity
        android:id="@+id/activity"
        android:name="com.example.jatpack.navigation.NavigationActivity"
        android:label="activity_second"
        tools:layout="@layout/activity_navigation" >
    </activity>
</navigation>

FirstFragment.xml
增加跳转到activity的操作，并在跳转到fragment的操作中传值

public class FirstFragment extends Fragment {
 
    public FirstFragment() {
        // Required empty public constructor
    }
 
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_first, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        //跳转到下一个fragment, 并传值
        Button btnNext = view.findViewById(R.id.btn_next);
        btnNext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                  Bundle bundle = new Bundle();
                  bundle.putString("name","from firstFragment");
                Navigation.findNavController(v).navigate(R.id.action_firstFragment_to_secondFragment,bundle);
            }
        });
       //跳转到activity
       Button btnJumpA = view.findViewById(R.id.btn_jumpA);
        btnJumpA .setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Navigation.findNavController(v).navigate(R.id.action_firstFragment_to_activity);
            }
        });
    }
}

SecondFragment接收传来的值

public class SecondFragment extends Fragment {
 
    public SecondFragment() {
        // Required empty public constructor
    }
 
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_second, container, false);
    }
 
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Button btnBack = view.findViewById(R.id.btn_back);
        btnBack.setOnClickListener(new View.OnClickListener(){
 
            @Override
            public void onClick(View v) {
                Navigation.findNavController(v).navigateUp();
            }
        });
        TextView tv_tip = view.findViewById(R.id.tv_tip);
        Bundle bundle = getArguments();
        if(bundle.getString("name") != null) {
            String name = bundle.getString("name");
            tv_tip.setText("This is secondFragment, "+name);
        }
    }
}