出现FC

[dodola]

Device：Google Nexus 7
Android Version：4.2.2

重现方法：点进文章后查看，后退，重复几次后可重现,View包里的几个Fragment均有此现象

Exception：

05-04 15:08:37.827: E/AndroidRuntime(10973): FATAL EXCEPTION: main
05-04 15:08:37.827: E/AndroidRuntime(10973): java.lang.RuntimeException: Unable to start activity ComponentInfo{cn.eoe.app/cn.eoe.app.ui.MainActivity}: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment cn.eoe.app.view.WikiFragment: make sure class name exists, is public, and has an empty constructor that is public
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3692)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.ActivityThread.access$700(ActivityThread.java:141)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1240)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.os.Looper.loop(Looper.java:137)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.ActivityThread.main(ActivityThread.java:5041)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at java.lang.reflect.Method.invokeNative(Native Method)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at java.lang.reflect.Method.invoke(Method.java:511)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at dalvik.system.NativeStart.main(Native Method)
05-04 15:08:37.827: E/AndroidRuntime(10973): Caused by: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment cn.eoe.app.view.WikiFragment: make sure class name exists, is public, and has an empty constructor that is public
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.support.v4.app.Fragment.instantiate(Fragment.java:405)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.support.v4.app.FragmentState.instantiate(Fragment.java:97)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.support.v4.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1767)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:208)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at cn.eoe.app.ui.base.BaseFragmentActivity.onCreate(BaseFragmentActivity.java:15)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at cn.eoe.app.ui.base.BaseSlidingFragmentActivity.onCreate(BaseSlidingFragmentActivity.java:21)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at cn.eoe.app.ui.MainActivity.onCreate(MainActivity.java:132)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.Activity.performCreate(Activity.java:5104)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
05-04 15:08:37.827: E/AndroidRuntime(10973):    ... 12 more
05-04 15:08:37.827: E/AndroidRuntime(10973): Caused by: java.lang.InstantiationException: can't instantiate class cn.eoe.app.view.WikiFragment; no empty constructor
05-04 15:08:37.827: E/AndroidRuntime(10973):    at java.lang.Class.newInstanceImpl(Native Method)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at java.lang.Class.newInstance(Class.java:1319)
05-04 15:08:37.827: E/AndroidRuntime(10973):    at android.support.v4.app.Fragment.instantiate(Fragment.java:394)
05-04 15:08:37.827: E/AndroidRuntime(10973):    ... 21 more

[dodola]

Fragment 是需要一个默认构造方法的,在Fragment里添加一个无参的构造方法应该就可以

[rockybean]

一般推荐是在fragment中使用一个newInstance的方法，然后把传入的参数放在fragment本身的argument中，例如

public static YourFragment newInstance(String someArg){
            YourFragment rtn = new YourFragment();
             Bundle args = new Bundle();
             args.putString("argKey",someArg);
            rtn.setArgument(args);
            return rtn;
}

之后可以从fragment的getArgument()中获取存储的方法，这样就可以很好的避免上面的问题了

[IceskYsl]

楼上正解~　大家可以尝试修复下这个问题，然后发个pull　request〜

[com360]

大家快点发pull　request，我等着merge呢 ；）

[mjkohoh]

尝试重现bug失败。重现环境在nexus7的4,2,2版本和4.3都跑过了。都没有出现上述所说的Force Close。请问是不是已经修复这个bug了。但是我并没有找到相关提交。

[mjkohoh]

好吧这个issue的确还没有被修复。查了一下文档，出现FC的原因是因为在系统需要重新实例化fragment的时候需要一个空的构造方法。(这点之前的同学已经说过了，我又重述了一遍)，而我没有重现bug的原因可能是因为没有遇到系统重新实例化fragment吧。

以下是相关文档的引用

All subclasses of Fragment must include a public empty constructor. The framework will often re-instantiate a fragment class when needed, in particular during state restore, and needs to be able to find this constructor to instantiate it. If the empty constructor is not available, a runtime exception will occur in some cases during state restore.

---

对于@rockybean 的建议，我想说的是。这会不会对代码改动太大

[mjkohoh]

另外相似的问题也在issue #48 中出现。在issue #48 中解决办法是增加无参构造函数。
我想对于一个相同的问题应该采取相同的解决方法。所以有必要讨论一下到底是采用无参构造函数还是使用newInstance方法。

下面列出同样出同样有这个bug的fragment

• UserCollectFragment
• UserCollectListFragment
• UserIntroFragment
• UserLogOutFragment
• WikiFragment

[mjkohoh]

@IceskYsl @com360 你觉得采取哪种方法修复这个bug最好

[mjkohoh]

没有人愿意讨论一下的吗？
要不管理员做个决定？