newInstance() 模式

儘管可以使用引數建立片段建構函式，但 Android 在重新建立片段時會在內部呼叫零引數建構函式（例如，如果因為 Android 自身原因而被殺死後它們正在被恢復）。因此，不建議依賴具有引數的建構函式。

為了確保始終存在你期望的片段引數，你可以使用靜態 newInstance() 方法建立片段，並將你想要的任何引數放入建立新例項時可用的包中。

import android.os.Bundle;
import android.support.v4.app.Fragment;

public class MyFragment extends Fragment
{
  // Our identifier for obtaining the name from arguments
  private static final String NAME_ARG = "name";

  private String mName;

  // Required
  public MyFragment(){}

  // The static constructor.  This is the only way that you should instantiate
  // the fragment yourself
  public static MyFragment newInstance(final String name) {
    final MyFragment myFragment = new MyFragment();
    // The 1 below is an optimization, being the number of arguments that will
    // be added to this bundle.  If you know the number of arguments you will add
    // to the bundle it stops additional allocations of the backing map.  If
    // unsure, you can construct Bundle without any arguments
    final Bundle args = new Bundle(1);

    // This stores the argument as an argument in the bundle.  Note that even if
    // the 'name' parameter is NULL then this will work, so you should consider
    // at this point if the parameter is mandatory and if so check for NULL and
    // throw an appropriate error if so
    args.putString(NAME_ARG, name);

    myFragment.setArguments(args);
    return myFragment;
  }

  @Override
  public void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    final Bundle arguments = getArguments();
    if (arguments == null || !arguments.containsKey(NAME_ARG)) {
      // Set a default or error as you see fit
    } else {
      mName = arguments.getString(NAME_ARG);
    }
  }
}

現在，在活動中：

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
MyFragment mFragment = MyFragment.newInstance("my name");
ft.replace(R.id.placeholder, mFragment);
//R.id.placeholder is where we want to load our fragment
ft.commit();

此模式是確保在建立時將所有必需引數傳遞給片段的最佳實踐。請注意，當系統銷燬片段並稍後重新建立它時，它將自動恢復其狀態 - 但你必須為其提供 onSaveInstanceState(Bundle) 實現。