Fragment的跳转

第一个xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:orientation="vertical"
android:gravity="center"
tools:context="com.example.jzuo2.MainActivity">
<LinearLayout
    android:id="@+id/txt_show"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:orientation="vertical">
</LinearLayout>
<Button
    android:id="@+id/btn_show"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/btn_show"
    android:gravity="center"
    android:layout_gravity="center_horizontal"
    android:onClick="onClick"/>
<LinearLayout
    android:id="@+id/txt_show2"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:orientation="vertical">
</LinearLayout>
</LinearLayout>

第二个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"
tools:context="com.example.jzuo2.FirstFragment">

<!-- TODO: Update blank fragment layout -->
<TextView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:id="@+id/txt_first"
    android:text="@string/fragment_first"/>

</FrameLayout>

第三个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="com.example.jzuo2.SecondFragment">

<!-- TODO: Update blank fragment layout -->
<TextView
    android:id="@+id/txt_second"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:text="@string/fragment_second"/>

</FrameLayout>

主java

public class MainActivity extends AppCompatActivity {
FirstFragment FirstFragment;
SecondFragment SecondFragment;
private boolean qh = true;
private boolean tz = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    FragmentManager manager = getFragmentManager();
    FragmentTransaction transaction = manager.beginTransaction();

    FirstFragment = new FirstFragment();
    transaction.add(R.id.txt_show,FirstFragment);
    transaction.commit();
}
public void onClick(View view){
    if(view.getId() == R.id.btn_show){
        tz = true;
        if(qh) {
            FragmentManager manager = getFragmentManager();
            FragmentTransaction transaction = manager.beginTransaction();
            if (SecondFragment == null) {
                SecondFragment = new SecondFragment();
                transaction.replace(R.id.txt_show2, SecondFragment);
                transaction.commit();
                qh = false;
            } else {
                transaction.replace(R.id.txt_show2, SecondFragment);
                transaction.commit();
                qh = false;
            }
        }else{
    Toast.makeText(this,"This is second fragment",Toast.LENGTH_SHORT).show();
}

}
}

public boolean onKeyDown(int keyCode,KeyEvent event) {

    if(event.getKeyCode()==KeyEvent.KEYCODE_BACK&&tz){

        FragmentManager manager = getFragmentManager();
        FragmentTransaction transaction = manager.beginTransaction();
        qh = true;
        tz = false;
        transaction.replace(R.id.txt_show2,FirstFragment);
        transaction.commit();
        return  false;
    } else {
        finish();
    }
    return super.onKeyDown(keyCode,event);


}

}

第二个java与第三个类似

public class FirstFragment extends Fragment {
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View view = inflater.inflate(R.layout.fragment_first,container,false);
        return view;
    }

}