如何从 Itemclick 侦听器打开图像

Question

我试图在单击 GridView 中的元素时调用 activity 它会在滑动 activity 中打开，它会显示相应的图像，但我在设置时遇到错误作为

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.access0(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.access0(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

这是我在点击显示吐司但随后使我的片段代码崩溃的任何项目时遇到的错误

 @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;
}

我的扫码查看代码`

 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));
}`

这是我想开始的 activity，但是出现错误，谁能告诉我如何解决这个问题。

Answer 1

你的错误本身给出了你问题的答案。

requestFeature() must be called before adding content

这意味着您的第二个 Activity 需要此更改

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

requestWindowFeature() 必须在 setContentView()

之前

在你更新问题后

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

你需要检查这个What is a Null Pointer Exception, and how do I fix it?

Answer 2

像下面那样呼叫requestWindowFeature

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

Answer 3

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

Answer 4

问题出在这几行

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

First : check whether you have a ViewPager layout with id of viewpager1 in your activity_main4 xml

Second : how do you pass the images to your adapter ?! are there link or you pass drawable itself ?! you dnt pass anything to your adapter !!!!!!!!!!!!!

Third : when your adapter is empty , you cant use viewPager.setCurrentItem(getIntent().getIntExtra("pic", 0)); on it

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