在Android中的片段中设置图像时出现NullPointerException异常

Question

我试图从片段中ImageView中的drawable设置图像。上面的代码在线上抛出NullPointerException，

imageView.setImageResource（R.drawable.featured_one）;

public class FeaturedTwo extends Fragment { 

    ImageView imageView; 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 

     View rootView = inflater.inflate(R.layout.featured_one, container, false); 

     imageView = (ImageView) rootView.findViewById(R.id.featured_two_image); 

     imageView.setImageResource(R.drawable.featured_one); 

     return rootView; 

    } 
} 

请帮我找到一个解决方案。

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference 
                        at com.example.anandzoom.appytizertest.FeaturedTwo.onCreateView(FeaturedTwo.java:28) 
                        at android.support.v4.app.Fragment.performCreateView(Fragment.java:2189) 
                        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1299) 
                        at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1528) 
                        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1595) 

XML featured_one的，

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <ImageView 
     android:id="@+id/featured_one_image" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:scaleType="centerCrop" /> 

</LinearLayout> 

Answer 1

在片段用画面的内容，而不是getActivity()

编辑：并修补您的ImageView ID使用featured_one_image代替featured_one_image的。

public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 

    View rootView = inflater.inflate(R.layout.featured_one, container, false); 
    imageView = (ImageView) rootView.findViewById(R.id.featured_one_image); 

    // set drawable image like it 
    imageView.setImageDrawable(ContextCompat.getDrawable(getActivity(), R.drawable.featured_one)); 


    return rootView; 

} 

Answer 2

你需要找到从rootView的ImageView的。

呼叫

imageView = (ImageView) rootView.findViewById(R.id.featured_one_image);

编辑：您rootView内的ImageView的是featured_one_image，不featured_two_image

Answer 3

使用rootView.findViewById，而不是getActivity因为你的布局片段内部没有活动里面。

你也有错误的id，进入你的xml被命名为“featured_one_image”，但你会得到“featured_two_image”。

所以更改代码 imageView = (ImageView) rootView.findViewById(R.id.featured_two_image);与imageView = (ImageView) rootView.findViewById(R.id.featured_one_image);

Answer 4

嘿，你需要找到没有父活动片段中你的看法。

只需更换

imageView = (ImageView) getActivity().findViewById(R.id.featured_one_image); 

与

imageView = (ImageView) rootView.findViewById(R.id.featured_two_image); 

Answer 5

，而不是这样的：

imageView = (ImageView) getActivity().findViewById(R.id.featured_two_image); 

使用本：

imageView = (ImageView) rootView.findViewById(R.id.featured_two_image);