关于Fragment的应用

关于Fragment的应用
########这次的作业是实现利用Fragment实现界面跳转的功能。

这是界面布局的代码：

1）activity.xml

2）First fragment.xml的代码：

2）Second fragment.xml的代码：

2）Java的代码：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
FirstFragment firstFragment;
ScondFragment scondFragment;
private boolean a = true;
private boolean b = 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.show, firstFragment);
transaction.commit();
}

@Override
public void onClick(View v) {
if (v.getId() == R.id.btnshow) ;
a = true;
if (b) {
FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
if (scondFragment == null) {
scondFragment = new ScondFragment();
transaction.replace(R.id.show, scondFragment);
transaction.commit();
a = false;
} else {
transaction.replace(R.id.show, scondFragment);
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 && b) {
FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
a = true;
b = false;
transaction.replace(R.id.show, firstFragment);
transaction.commit();
return false;
} else {
finish();
}
return super.onKeyDown(keyCode, event);
}