Question

我用以下（和工作！）代码切换我的片段：

Fragment fragment = new DashboardFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.main_fragment, fragment);
fragmentTransaction.commit();

但是，当我调用此代码时（通常是因为它在导航栏中），会调用onCreateView函数。

由于new DashboardFragment();，我可以想象它，但我不知道我能改变什么。

是否可以一次创建片段并在下次访问它？

谢谢！

Answer 1

您可以使用Fragment找到之前添加的FragmentManager 当您第一次添加Fragment时，请为其添加标记，以便日后检索。这是这样做的：

fragmentTransaction.replace(R.id.main_fragment, fragment, "my_fragment_tag");

然后，只要您想获得fragment，只需使用以下代码：

FragmentManager fragmentManager = getSupportFragmentManager();
DashboardFragment dashboard = fragmentManager.findFragmentByTag("my_fragment_tag");
if(dashboard) {
    //Do whatever you want with the fragment
} else {

    dashboard = new DashboardFragment();
}

Answer 2

无论您如何尝试，在替换onCreateView后始终会调用Fragment方法，此方法会自动调用，因为它是lifecycle’s Fragment

的一部分

也就是说，您可以保存Fragment变量值来保存静态实例并通过静态初始化方法调用它：

private static SameInstanceFragment sameInstanceFragment;

public static SameInstanceFragment getInstance() {
    sameInstanceFragment = sameInstanceFragment == null ? new SameInstanceFragment() : sameInstanceFragment;
    return sameInstanceFragment;
}

在下一个示例中，您将看到每次实例化的Fragment如何无法保存其值，而已保存为唯一实例的那个可以执行此操作：

// SameInstanceFragment

public class SameInstanceFragment extends Fragment {

private static SameInstanceFragment sameInstanceFragment;
private int mCounter;

public static SameInstanceFragment getInstance() {
    sameInstanceFragment = sameInstanceFragment == null ? new SameInstanceFragment() : sameInstanceFragment;
    return sameInstanceFragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    mCounter++;
    return inflater.inflate(R.layout.test_fragment, null);
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    String feedback = " Member counter: " + mCounter;
    Toast.makeText(getActivity(), feedback, Toast.LENGTH_SHORT).show();
    //member variables preserve its value after replace 
}
}

// NewInstanceFragment

public class NewInstanceFragment extends Fragment {

private int mCounter;

public static NewInstanceFragment getInstance() {
    return new NewInstanceFragment();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    mCounter++;
    return inflater.inflate(R.layout.test_fragment, null);
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    String feedback = " Member counter: " + mCounter;
    Toast.makeText(getActivity(), feedback, Toast.LENGTH_SHORT).show();
    //member variables don’t preserve its value after replace 
}

}

// TestFragmentActivity

public class TestFragmentActivity extends FragmentActivity {

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

    switchFragment();
    setListener();
}

private void setListener() {
    findViewById(R.id.tb_switch_fragment).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            switchFragment();
        }
    });
}

private void switchFragment() {
    Fragment fragmentDisplayed = getCurrentFragmentDisplayed();
    Fragment fragmentToSwitch = null;
    if (fragmentDisplayed == null)
        fragmentToSwitch = SameInstanceFragment.getInstance();
    else if(fragmentDisplayed instanceof SameInstanceFragment)
        fragmentToSwitch = NewInstanceFragment.getInstance();
    else
        fragmentToSwitch = SameInstanceFragment.getInstance();
    setFragment(fragmentToSwitch);
}

private void setFragment(Fragment fragment) {
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.fl_container, fragment);
    fragmentTransaction.commit();
}

public Fragment getCurrentFragmentDisplayed(){
    List<Fragment> fragments = getSupportFragmentManager().getFragments();
    if(fragments == null) return null;
    for (Fragment fragment : fragments) {
        if(fragment.isVisible()) return fragment;
    }
    return null;
}
}

Answer 3

当然，创建一个成员变量和一个检索它的方法，如下所示：

private DashboardFragment fragment;

private DashboardFragment getFragment() {
  if (fragment == null)
    fragment = new DashboardFragment();

  return fragment;
}

然后，当您想要访问该片段时，请使用new DashboardFragment()而不是getFragment()。

更改Android片段而不创建新片段

3 个答案: