Fragment的跳转

第一个xml

第二个xml

第三个xml

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;
}

}