【Android策略决】Fragment实例化及通过setArguments解决 android.support.v4.app.Fragment$InstantiationException

Caused by: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.storm.durian.f.c: make sure class name exists, is public, and has an empty constructor that is public

翻译一下就是：不能够实例化Fragment，请确定类名存在且是公共类，并且有一个公共的构造函数

首先这个问题不必现，出现了有可能导致应用页面崩溃

先看一下导致这个问题的代码

 public static FavoriteAndFansFragment newInstance(String uid, boolean isSelfUser, int type) {FavoriteAndFansFragment f = new FavoriteAndFansFragment(uid, isSelfUser, type);return f;} public FavoriteAndFansFragment (String uid, boolean isSelfUser, int type) {super();    this.uid = uid;this.isSelfUser = isSelfUser;this.type = type;if (type == 0) {    url = UrlContainer.USER_FOLLOWER_URL;}else{    url = UrlContainer.USER_FANS_URL;}}/** * When creating, retrieve this instance's number from its arguments. */@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);}

再看一下优化后的代码

  /** * Create a new instance of Fragment, providing para as an * argument. */ public static FavoriteAndFansFragment newInstance(String uid, boolean isSelfUser, int type) {FavoriteAndFansFragment f = new FavoriteAndFansFragment();        Bundle args = new Bundle();        args.putString("uid", uid);        args.putBoolean("isSelfUser", isSelfUser);        args.putInt("type", type);        f.setArguments(args);        return f;}/** * When creating, retrieve this instance's para from its arguments. */@Override public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        Bundle bundle = getArguments();        if (bundle != null) {            uid = bundle.getString("uid");            isSelfUser = bundle.getBoolean("isSelfUser");            type = bundle.getInt("type");            if (type == 0) {                url = UrlContainer.USER_FOLLOWER_URL;            } else {                url = UrlContainer.USER_FANS_URL;            }        }    }

分析：

1、官方推荐Fragment.setArguments(Bundle bundle)这种方式来传递参数，而不推荐通过构造方法直接来传递参数，why？

2、当一个fragment重新创建的时候，系统会再次调用 Fragment中的默认构造函数

3、什么时候会重新创建fragment，when设备配置参数发生变化（如：横竖屏切换），

4、既然是调用默认构造函数，那么通过重载传递的参数将全部丢失

5、而使用系统推荐的 Fragment.setArguments（Bundle）来传递参数。就可以有效的避免这一个问题，当你的Fragment销毁的时候，其中的Bundle会保存下来，当要重新创建的时候会检查Bundle是否为null，如果不为null，就会使用bundle作为参数来重新创建fragment.

6、setArguments can only be called before the Fragment is attached to the Activity.

setArguments方法的调用必须要在Fragment与Activity关联之前，即setArgument方法的使用必须要在FragmentTransaction 的commit之前使用

public class FavAndFansActivity extends BaseActivity {private static final String TAG = "FavAndFansActivity";@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_other_user_info);String uid = getIntent().getStringExtra("uid");boolean isSelf = getIntent().getBooleanExtra("isSelf", false);int type = getIntent().getIntExtra("type", 0);FragmentManager fm = getSupportFragmentManager();if (fm.findFragmentByTag(TAG) == null) {FragmentTransaction ft = fm.beginTransaction();ft.add(R.id.other_user_layout, FavoriteAndFansFragment.newInstance(uid, isSelf, type), TAG).commit();}}}

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