Question

我试图在点击GridView中的某个元素时调用某个活动它将在滑动活动中打开，它将显示相应的图像，但我在设置时收到错误如

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.union.project, PID: 2194
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.union.project/com.union.project.Swipeview.Main4Activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
 at android.app.ActivityThread.access$800(ActivityThread.java:151)
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
 at android.os.Handler.dispatchMessage(Handler.java:102)
 at android.os.Looper.loop(Looper.java:135)
 at android.app.ActivityThread.main(ActivityThread.java:5254)
 at java.lang.reflect.Method.invoke(Native Method)
 at java.lang.reflect.Method.invoke(Method.java:372)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
 at com.union.project.Swipeview.Main4Activity.onCreate(Main4Activity.java:26)
 at android.app.Activity.performCreate(Activity.java:5990)
 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
 at android.app.ActivityThread.access$800(ActivityThread.java:151) 
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
 at android.os.Handler.dispatchMessage(Handler.java:102) 
 at android.os.Looper.loop(Looper.java:135) 
 at android.app.ActivityThread.main(ActivityThread.java:5254) 
 at java.lang.reflect.Method.invoke(Native Method) 
 at java.lang.reflect.Method.invoke(Method.java:372) 
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
 04-27 01:17:54.025 2194-2194/com.union.project I/Process: S

这是我点击anyitem时显示吐司然后崩溃我的片段代码的错误

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view= inflater.inflate(R.layout.fragment_two, container, false);
    GridView gridView=(GridView)view.findViewById(R.id.gridView2);
    gridView.setAdapter(new UAdapter(getActivity()));
    gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Toast.makeText(getActivity(),"Pic"+(position)+"Selected",Toast.LENGTH_SHORT).show();
            Intent intent= new Intent(view.getContext(),Main4Activity.class);
            intent.putExtra("pic",position);
            startActivity(intent);
        }
    });
    return view;
}

我的滑动视图代码`

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main4);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    viewPager =(ViewPager)findViewById(R.id.viewpager1);
    adapter =new CustomeSwipeAdapter2(this);
    viewPager.setAdapter(adapter);
    viewPager.setCurrentItem(getIntent().getIntExtra("pic", 0));
}`

这是我想要开始的活动但是得到错误可以告诉我如何解决这个问题。

Answer 1

您的错误本身会回答您的问题。

requestFeature() must be called before adding content

这意味着您的第二个活动需要此更改

requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main4);

requestWindowFeature()必须在setContentView()

之前

更新后的问题

现在你的错误是

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference

您需要查看此What is a Null Pointer Exception, and how do I fix it?

Answer 2

像{@ p>一样呼叫requestWindowFeature

@Override
public void onCreate(Bundle savedInstanceState) {
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.mainmenu);
}

Answer 3

如上所述，您需要调用requestWindowFeature（Window.FEATURE_NO_TITLE）;在setContentView方法之前。

Answer 4

问题出在这些方面

viewPager =(ViewPager)findViewById(R.id.viewpager1);
adapter =new CustomeSwipeAdapter2(this);
viewPager.setAdapter(adapter);
viewPager.setCurrentItem(getIntent().getIntExtra("pic", 0));

首先：检查您的activity_main4 xml中是否有一个id为viewpager1的ViewPager布局

第二：如何将图像传递给适配器？是否有链接或你自己通过drawable？！你没有把任何东西传递给你的适配器!!!!!!!!!!!!!

第三：当您的适配器为空时，您无法使用viewPager.setCurrentItem(getIntent().getIntExtra("pic", 0));    在它上面

如何从Itemclick监听器打开图像

4 个答案: