blocks|key|4328267|text|您的活动context在这一行中为空：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|4328268|Toast.makeText(getActivity(),+"Connection+Failure",+Toast.LENGTH_LONG).show();//+getActivity()+is+null|code-block|syntax|javascript|4328269|为了避免崩溃，请使用以下命令：|4328270|if(getActivity()+!=+null)
+++Toast.makeText(getActivity(),+"Connection+Failure",+Toast.LENGTH_LONG).show();|4328271|entityMap^0|4|7|4|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|W|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|X|8|@]|E|@]|F|$]]|$1|N|3|O|5|I|7|Y|8|@]|E|@]|F|$J|K]]|$1|P|3|-4|5|6|7|Z|8|@]|E|@]|F|$]]]|Q|$]]

Your activity <code>context</code> is null in this line :

<pre><code>Toast.makeText(getActivity(), "Connection Failure", Toast.LENGTH_LONG).show();// getActivity() is null
</code></pre>

To avoid crash use this :

<pre><code>if(getActivity() != null)
 Toast.makeText(getActivity(), "Connection Failure", Toast.LENGTH_LONG).show();
</code></pre>

blocks|key|1713512|text|有时，当片段与活动无关时，getActivity()或getContext()可能会产生空指针异常。所以使用onAttach方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1713513|public+class+yourFragment+extends+Fragment+{
+++Context+context

+++@Override
+++public+void+onAttach(Context+context)+{
++++++++this.context+=+context;
++++++++super.onAttach(context);
+++}
}|code-block|syntax|javascript|1713514|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|$]]

Sometimes getActivity() or getContext() may produce a null pointer exception when the fragment is not associated with an Activity. So use the onAttach method

<pre><code>public class yourFragment extends Fragment {
 Context context

 @Override
 public void onAttach(Context context) {
 this.context = context;
 super.onAttach(context);
 }
}
</code></pre>

blocks|key|1713527|text|将getActivity()更改为getContext()。尝试以下给定的代码：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1713528|Toast.makeText(getContext(),+"Connection+Failure",+Toast.LENGTH_LONG).show();|code-block|syntax|javascript|1713529|entityMap^0|1|D|H|C|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

Change your <code>getActivity()</code> to <code>getContext()</code>. try the given code below:

<pre><code>Toast.makeText(getContext(), "Connection Failure", Toast.LENGTH_LONG).show();
</code></pre>

blocks|key|676444|text|也许getActivity()是在碎片分离时调用的。试试看。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|676445|if+(isAdded())+{
++++Toast.makeText(getActivity(),+"something",+Toast.LENGTH_SHORT).show();
}|code-block|syntax|javascript|676446|entityMap^0|2|D|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Maybe <code>getActivity()</code> called when fragment detached. Try it.

<pre><code>if (isAdded()) {
 Toast.makeText(getActivity(), "something", Toast.LENGTH_SHORT).show();
}
</code></pre>

blocks|key|4328318|text|根据Fragment.getActivity()的代码&+javadoc，您可以返回null：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4328319|/**
+*+Return+the+{@link+FragmentActivity}+this+fragment+is+currently+associated+with.
+*+May+return+{@code+null}+if+the+fragment+is+associated+with+a+{@link+Context}
+*+instead.
+*
+*+@see+#requireActivity()
+*/
@Nullable
final+public+FragmentActivity+getActivity()+{
++++return+mHost+==+null+?+null+:+(FragmentActivity)+mHost.getActivity();
}|code-block|syntax|javascript|4328320|特别是当您的片段没有附加到某个活动时(如here和here所指出的)，可能会发生这种情况。|4328321|同样，getContext()也可以返回null。|4328322|在这个可能相关的帖子中，我们很好地讨论了这些值何时为空：|4328323|Why+getContext()+in+fragment+sometimes+returns+null?|unordered-list-item|4328324|The+simple+solution+has+been+provided+already+-在显示Toast之前进行空检查。|4328325|但根本的问题是体系结构--您的代码正在将API活动耦合到您的UI中，并且假设您的UI状态的某些内容--即假设当API调用返回时，用户仍然可以看到您的屏幕。|4328326|一个更好的解决方案是将Retrofit调用与UI+-+put+the+API+calls+in+a+separate+class+that+does+not+depend+on+the+UI+state分离。|4328327|使用事件或发布子框架从这个API包装类向任何需要知道API调用何时返回的UI组件进行通信。|4328328|EventBus或RxJava将是这方面的两种常见解决方案(LocalBroadcastManager将是一种较不常见的方法)。|4328329|这将允许任何代码调用您的API，并在API返回时通知订阅。|4328330|它还允许您将API响应保存在(例如)本地数据库中，在这种情况下，您只需依赖LiveData模式来更新任何需要的UI。|4328331|+pattern.|4328332|考虑到某些项目无法立即重新设计，可能需要解决办法。|4328333|上面提到的null检查解决方法很有用，因为应用程序不会再崩溃。不幸的是，这确实意味着用户不会被通知失败的API调用。|4328334|另一种选择是创建您自己的Application子类(为了初始化公共库，许多项目已经这样做了)，并为静态访问此应用程序Context提供了一种方法。(A+similar+suggestion+has+subsequently+been+made+by+Kushal.)|4328335|然后可以选择使用应用程序Toast来显示Context，而不是使用片段中的应用程序Context。您可能会失去从更具体的上下文中获得的任何特定样式，但好处是您的用户仍然可以看到Toast消息。|4328336|本文很好地描述了将您的Application公开为单例的情况：|4328337|Application+singleton+use+in+Android|4328338|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/52289963/383414|1|https://stackoverflow.com/a/52290086/383414|2|https://stackoverflow.com/questions/47987649/why-getcontext-in-fragment-sometimes-returns-null|3|https://stackoverflow.com/a/52289823/383414|4|https://stackoverflow.com/questions/26239650/best-way-to-decouple-rest-call-from-activity|5|https://medium.com/@amtechnovation/android-architecture-component-mvvm-part-1-a2e7cff07a76|6|https://stackoverflow.com/questions/52289744/toast-in-android-fragments-showing-null-pointer-expn/52290176#comment91529291_52289744|7|https://stackoverflow.com/a/43200077/383414^0|2|M|16|4|0|0|K|4|0|P|4|1|0|3|C|0|0|0|1G|2|0|1E|5|0|19|3|0|0|R|22|4|0|0|0|8|9|6|U|L|0|0|11|8|0|0|9|5|0|0|0|C|B|1M|7|21|1O|6|0|C|5|K|7|15|7|2G|5|0|B|B|0|0|10|7|0^^$0|@$1|2|3|4|5|6|7|27|8|@$9|28|A|29|B|C]|$9|2A|A|2B|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|2C|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|2D|8|@]|D|@$9|2E|A|2F|1|2G]|$9|2H|A|2I|1|2J]]|E|$]]|$1|M|3|N|5|6|7|2K|8|@$9|2L|A|2M|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|2N|8|@]|D|@]|E|$]]|$1|Q|3|R|5|S|7|2O|8|@]|D|@$9|2P|A|2Q|1|2R]]|E|$]]|$1|T|3|U|5|6|7|2S|8|@$9|2T|A|2U|B|C]]|D|@$9|2V|A|2W|1|2X]]|E|$]]|$1|V|3|W|5|6|7|2Y|8|@]|D|@]|E|$]]|$1|X|3|Y|5|6|7|2Z|8|@]|D|@$9|30|A|31|1|32]]|E|$]]|$1|Z|3|10|5|6|7|33|8|@]|D|@]|E|$]]|$1|11|3|12|5|6|7|34|8|@$9|35|A|36|B|C]|$9|37|A|38|B|C]|$9|39|A|3A|B|C]]|D|@]|E|$]]|$1|13|3|14|5|6|7|3B|8|@]|D|@]|E|$]]|$1|15|3|16|5|6|7|3C|8|@$9|3D|A|3E|B|C]]|D|@]|E|$]]|$1|17|3|18|5|6|7|3F|8|@]|D|@$9|3G|A|3H|1|3I]]|E|$]]|$1|19|3|1A|5|6|7|3J|8|@]|D|@]|E|$]]|$1|1B|3|1C|5|6|7|3K|8|@]|D|@]|E|$]]|$1|1D|3|1E|5|6|7|3L|8|@$9|3M|A|3N|B|C]|$9|3O|A|3P|B|C]]|D|@$9|3Q|A|3R|1|3S]]|E|$]]|$1|1F|3|1G|5|6|7|3T|8|@$9|3U|A|3V|B|C]|$9|3W|A|3X|B|C]|$9|3Y|A|3Z|B|C]|$9|40|A|41|B|C]]|D|@]|E|$]]|$1|1H|3|1I|5|6|7|42|8|@$9|43|A|44|B|C]]|D|@]|E|$]]|$1|1J|3|1K|5|S|7|45|8|@]|D|@$9|46|A|47|1|48]]|E|$]]|$1|1L|3|-4|5|6|7|49|8|@]|D|@]|E|$]]]|1M|$1N|$5|1O|1P|1Q|E|$1R|1S]]|1T|$5|1O|1P|1Q|E|$1R|1U]]|1V|$5|1O|1P|1Q|E|$1R|1W]]|1X|$5|1O|1P|1Q|E|$1R|1Y]]|1Z|$5|1O|1P|1Q|E|$1R|20]]|21|$5|1O|1P|1Q|E|$1R|22]]|23|$5|1O|1P|1Q|E|$1R|24]]|25|$5|1O|1P|1Q|E|$1R|26]]]]

According to the code &amp; javadoc for <code>Fragment.getActivity()</code> you can get <code>null</code> returned:

<pre><code>/**
 * Return the {@link FragmentActivity} this fragment is currently associated with.
 * May return {@code null} if the fragment is associated with a {@link Context}
 * instead.
 *
 * @see #requireActivity()
 */
@Nullable
final public FragmentActivity getActivity() {
 return mHost == null ? null : (FragmentActivity) mHost.getActivity();
}
</code></pre>

Particularly this could happen when your Fragment is not attached to an activity (as pointed out <a href="https://stackoverflow.com/a/52289963/383414">here</a> and <a href="https://stackoverflow.com/a/52290086/383414">here</a>).

Similarly, <code>getContext()</code> can also return null.

There's a good discussion on when these can be null on this possibly related post:

<ul>
<li><a href="https://stackoverflow.com/questions/47987649/why-getcontext-in-fragment-sometimes-returns-null">Why getContext() in fragment sometimes returns null?</a></li>
</ul>

<hr>

<a href="https://stackoverflow.com/a/52289823/383414">The simple solution has been provided already</a> - put in a null check before displaying the <code>Toast</code>.

But the underlying problem is one of architecture - your code is coupling API activity to your UI, and assuming certain things about your UI state i.e. you are assuming that when the API call returns, your screen is still visible to the user.

<hr>

A better solution would be to decouple the Retrofit call from the UI - <a href="https://stackoverflow.com/questions/26239650/best-way-to-decouple-rest-call-from-activity">put the API calls in a separate class that does not depend on the UI state</a>.

Use an event or pub-sub framework to communicate from this API wrapper class back to any UI components that need to know when an API call returns. 

<code>EventBus</code> or <code>RxJava</code> would be 2 common solutions for this (<code>LocalBroadcastManager</code> would be a less common approach). 

This will allow any code to call into your API, and to subscribe to be notified when the API returns. 

It also allows you to save your API responses in (for example) a local database, in which case you could just rely on the <code>LiveData</code> pattern to update any UI that needs to be. 

<a href="https://medium.com/@amtechnovation/android-architecture-component-mvvm-part-1-a2e7cff07a76" rel="nofollow noreferrer">Here's a Medium article giving a brief description of how to use the Android Architecture Components in this manner using the <code>Repository</code> pattern.</a>

<hr>

Given that some projects cannot be redesigned immediately, there may be need for workarounds. 

The above mentioned null check workaround is useful in that the app will no longer crash. Unfortunately it does mean that the user will not be alerted to the failed API call.

One alternative is to create your own <code>Application</code> subclass (many projects will already have done this in order to initialise common libraries) and provide a method for static access to this application <code>Context</code>. <a href="https://stackoverflow.com/questions/52289744/toast-in-android-fragments-showing-null-pointer-expn/52290176#comment91529291_52289744">(A similar suggestion has subsequently been made by Kushal.)</a>

You could then choose to display the <code>Toast</code> using the application <code>Context</code> instead of the one from the fragment. You may lose any specific styling that would have been gained from the more specific context, but the advantage would be that your user still gets to see the <code>Toast</code> message.

Exposing your <code>Application</code> as a singleton has been described very nicely on this post:

<ul>
<li><a href="https://stackoverflow.com/a/43200077/383414">Application singleton use in Android</a></li>
</ul>

blocks|key|4328399|text|if+(isAdded())+{
++++Toast.makeText(getActivity(),+"something",+Toast.LENGTH_SHORT).show();
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4328400|或者试试这个|unstyled|4328401|if(getActivity()+!=+null)
+++Toast.makeText(getActivity(),+"Connection+Failure",+Toast.LENGTH_LONG).show();|4328402|在我的例子中，两者都会正常工作，因为在某些情况下，当片段分离时调用getActivity()。|offset|length|style|CODE|4328403|所以我们也要处理这件事。|4328404|entityMap^0|0|0|0|X|D|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|T|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|V|8|@$K|W|L|X|M|N]]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|F|7|Z|8|@]|9|@]|A|$]]]|R|$]]

<pre><code>if (isAdded()) {
 Toast.makeText(getActivity(), "something", Toast.LENGTH_SHORT).show();
}
</code></pre>

or try this 

<pre><code>if(getActivity() != null)
 Toast.makeText(getActivity(), "Connection Failure", Toast.LENGTH_LONG).show();
</code></pre>

Both will work fine in my case because in some case <code>getActivity()</code> called when fragment detached.

So we have to take care of that as well.

I am getting errors on few devices where I am trying to display a toast inside fragments. this toast is usually on retrofit response failure. toast code is simple. Please suggest, could not find any reason searching here and there.

<pre><code>Toast.makeText(getActivity(), "Connection Failure", Toast.LENGTH_LONG).show();
</code></pre>

and my ST logs are below.

<pre><code>Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
 at android.widget.Toast.(Toast.java:103)
 at android.widget.Toast.makeText(Toast.java:256)
</code></pre>

Toast in Android fragments showing null pointer expn

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我在一些设备上遇到错误，在这些设备中，我试图在片段中显示祝酒词。这篇祝酒词通常是关于改造反应失败的。吐司代码很简单。请建议，找不到任何理由到处寻找。Toast.makeText(getActivity(), "Connection Failure", Toast.LENGTH_LONG).show();我的ST记录在下...

问显示空指针expn的Android片段中的Toast
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