Fragment界面跳转

这个Fragment界面跳转我觉得是比较难的，因为班上好多人都没有做好，我也不太会做，参考了做好了的同学的作业，马马虎虎做好了。
这是主界面xml的代码：

运行的结果： 

JAVA代码：
package com.example.jkq.myapplication;

import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
Jkq1Fragment jkq1Fragment;
Jkq2Fragment jkq2Fragment;
private boolean a=true;
boolean e=false;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
jkq1Fragment = new Jkq1Fragment();
transaction.add(R.id.show,jkq1Fragment);
transaction.commit();
}

@Override
public void onClick(View view) {
if(view.getId()==R.id.bt_show){
e=true;
if(a){
FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
if (jkq2Fragment == null){
jkq2Fragment = new Jkq2Fragment();
transaction.replace(R.id.show,jkq2Fragment);
transaction.commit();
a=false;
} else{
transaction.replace(R.id.show,jkq2Fragment);
transaction.commit();
a=false;
}
}else{
Toast.makeText(this,"This is second fragment",Toast.LENGTH_SHORT).show();
}
}
}

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if(event.getKeyCode()==KeyEvent.KEYCODE_BACK&&e){
FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
a=true;
e=false;
transaction.replace(R.id.show,jkq1Fragment);
transaction.commit();
return false;
} else {
finish();
}
return super.onKeyDown(keyCode, event);
}

以及Fragment的相关代码：
（1）

（2）

（1.1）java package com.example.jkq.myapplication;

import android.app.Fragment;
import android.os.Bundle;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**

• A simple {@link Fragment} subclass.
  */
  public class Jkq2Fragment extends Fragment {

  public Jkq2Fragment() {
  // 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_jkq2, container, false);
  }

}
(2.2)java:
package com.example.jkq.myapplication;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**

• A simple {@link Fragment} subclass.
  */
  public class Jkq1Fragment extends Fragment {

  public Jkq1Fragment() {
  // 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_jkq1, container, false);
  }

}
运行的结果：

真的不会做啊 感觉跟不上