blocks|key|278269|text|创建一个包对象并插入您的数据(在本例中是您的Category对象)。请注意，您不能将此对象直接传递到bundle中，除非它是可序列化的。我认为更好的做法是在片段中构建对象，并只将id或其他内容放入包中。下面是创建和附加bundle的代码：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|278270|Bundle+args+=+new+Bundle();
args.putLong("key",+value);
yourFragment.setArguments(args);|code-block|syntax|javascript|278271|之后，在您的片段访问数据中：|278272|Type+value+=+getArguments().getType("key");|278273|就这样。|278274|entityMap^0|M|8|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|Y|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

Make a bundle object and insert your data (in this example your <code>Category</code> object). Be careful, you can't pass this object directly into the bundle, unless it's serializable.
I think it's better to build your object in the fragment, and put only an id or something else into bundle. This is the code to create and attach a bundle:

<pre><code>Bundle args = new Bundle();
args.putLong("key", value);
yourFragment.setArguments(args);
</code></pre>

After that, in your fragment access data:

<pre><code>Type value = getArguments().getType("key");
</code></pre>

That's all.

blocks|key|495230|text|由于FragmentManager实例化它的方式，你的Fragment不应该有构造函数。您应该有一个使用所需参数定义的newInstance()静态方法，然后将它们捆绑在一起，并将它们设置为片段的参数，稍后可以使用Bundle参数访问这些参数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|495231|例如：|495232|public+static+MyFragment+newInstance(int+title,+String+message)+{
++++MyFragment+fragment+=+new+MyFragment();
++++Bundle+bundle+=+new+Bundle(2);
++++bundle.putInt(EXTRA_TITLE,+title);
++++bundle.putString(EXTRA_MESSAGE,+message);
++++fragment.setArguments(bundle);
++++return+fragment+;
}|code-block|syntax|javascript|495233|并在onCreate上阅读这些论点|495234|@Override
public+void+onCreate(Bundle+savedInstanceState)+{
++++super.onCreate(savedInstanceState);
++++title+=+getArguments().getInt(EXTRA_TITLE);
++++message+=+getArguments().getString(EXTRA_MESSAGE);

++++//...
}|495235|这样，如果分离并重新附加，则可以通过参数存储对象状态，这与附加到Intent的bundles非常相似。|495236|entityMap^0|2|F|R|8|1N|D|2Z|6|0|0|0|2|8|0|0|W|6|13|7|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|T|$]]

Your <code>Fragment</code> shouldn't have constructors because of how the <code>FragmentManager</code> instantiates it. 
You should have a <code>newInstance()</code> static method defined with the parameters you need, then bundle them and set them as the arguments of the fragment, which you can later access with the <code>Bundle</code> parameter.

For example:

<pre><code>public static MyFragment newInstance(int title, String message) {
 MyFragment fragment = new MyFragment();
 Bundle bundle = new Bundle(2);
 bundle.putInt(EXTRA_TITLE, title);
 bundle.putString(EXTRA_MESSAGE, message);
 fragment.setArguments(bundle);
 return fragment ;
}
</code></pre>

And read these arguments at <code>onCreate</code>:

<pre><code>@Override
public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 title = getArguments().getInt(EXTRA_TITLE);
 message = getArguments().getString(EXTRA_MESSAGE);

 //...
}
</code></pre>

This way, if detached and re-attached, the object state can be stored through the arguments, much like <code>bundles</code> attached to <code>Intent</code>s.

blocks|key|495263|text|似乎没有一个答案真正回答了“为什么使用bundle传递参数而不是非默认构造函数”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|495264|之所以应该通过捆绑包传递参数，是因为当系统恢复fragment时(例如，在配置更改时)，它将自动恢复您的bundle。|offset|length|style|CODE|495265|像onCreate或onCreateView这样的回调应该从bundle中读取参数-这样就可以保证将fragment的状态正确地恢复到初始化fragment时所使用的状态(请注意，此状态可以与传递给onCreate/onCreateView的onSaveInstanceState+bundle不同)|495266|使用静态newInstance()方法的推荐只是一个推荐。您可以使用非默认构造函数，但请确保在该构造函数的主体内的bundle中填充了初始化参数。并在onCreate()或onCreateView()方法中读取这些参数。|495267|entityMap^0|0|N|8|1G|6|0|1|8|A|C|U|6|1E|8|1Y|8|2R|L|3D|Q|0|4|D|1L|6|23|A|2E|E|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@$D|P|E|Q|F|G]|$D|R|E|S|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|T|8|@$D|U|E|V|F|G]|$D|W|E|X|F|G]|$D|Y|E|Z|F|G]|$D|10|E|11|F|G]|$D|12|E|13|F|G]|$D|14|E|15|F|G]|$D|16|E|17|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|18|8|@$D|19|E|1A|F|G]|$D|1B|E|1C|F|G]|$D|1D|E|1E|F|G]|$D|1F|E|1G|F|G]]|9|@]|A|$]]|$1|L|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]]|M|$]]

It seems like none of the answers actually answer "why use bundle for passing parameters rather than non default constructors"

The reason why you should be passing parameters through bundle is because when the system restores a <code>fragment</code> (e.g on config change), it will automatically restore your <code>bundle</code>. 

The callbacks like <code>onCreate</code> or <code>onCreateView</code> should read the parameters from the <code>bundle</code> - this way you are guaranteed to restore the state of the <code>fragment</code> correctly to the same state the <code>fragment</code> was initialised with (note this state can be different from the <code>onSaveInstanceState bundle</code> that is passed to the <code>onCreate/onCreateView</code>)

The recommendation of using the static <code>newInstance()</code> method is just a recommendation. You can use a non default constructor but make sure you populate the initialisation parameters in the <code>bundle</code> inside the body of that constructor. And read those parameters in the <code>onCreate()</code> or <code>onCreateView()</code> methods.

blocks|key|278381|text|如果您对某些类使用参数。尝尝这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|278382|SomeClass+mSomeInstance;
public+static+final+MyFragment+newInstance(SomeClass+someInstance){
++++MyFragment+f+=+new+MyFragment();
++++f.mSomeInstance+=+someInstance;
++++return+f;
}|code-block|syntax|javascript|278383|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If you use parameter for some class. try this

<pre><code>SomeClass mSomeInstance;
public static final MyFragment newInstance(SomeClass someInstance){
 MyFragment f = new MyFragment();
 f.mSomeInstance = someInstance;
 return f;
}
</code></pre>

blocks|key|495317|text|我认为，静态构造函数和两个构造函数(空的和参数化的，将参数存储到片段的参数包中)没有区别，最有可能的是，这个经验法则是为了减少在Java中忘记实现无参数构造函数的概率，当存在重载时，不会隐式生成无参数构造函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|495318|在我的项目中，我使用Kotlin，并使用主无参数构造器和辅助参数构造器实现片段，这些构造器只是将它们存储到包中并将其设置为片段参数，一切都很好。|495319|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

I think, there is no difference between static constructor and two constructors (empty and parametrized one that stores arguments into a Fragment's arguments bundle), most probably, this rule of thumb is created to reduce probability of forgetting to implement no-arg constructor in Java, which is not implicitly generated when overload present. 

In my projects I use Kotlin, and implement fragments with a primary no-arg constructor and secondary constructor for arguments which just stores them into a bundle and sets it as Fragment arguments, everything works fine.

blocks|key|495332|text|如果片段在配置更改后使用非默认构造函数，则片段将丢失所有数据。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|495333|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If fragment uses non-default constructors after configuration changing the fragment will lose all data.

I am creating an app with <code>Fragments</code> and in one of them, I created a non-default constructor and got this warning:

<pre><code>Avoid non-default constructors in fragments: use a default constructor plus Fragment#setArguments(Bundle) instead
</code></pre>

Can someone tell me why this is not a good idea? 

Can you also suggest how I would accomplish this:

<pre><code>public static class MenuFragment extends ListFragment {
 public ListView listView1;
 Categories category;

 //this is my "non-default" constructor
 public MenuFragment(Categories category){
 this.category = category;
 }....
</code></pre>

Without using the non-default constructor?

Why do I want to avoid non-default constructors in fragments?

Kotlin

Java

我正在使用Fragments创建一个应用程序，在其中一个应用程序中，我创建了一个非默认构造函数，并收到以下警告：Avoid non-default constructors in fragments: use a default constructor plus Fragment#setArguments(Bundle...

问为什么我要避免在片段中使用非默认构造函数？
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