Java 空对象引用上的 void android.support.v4.app.Fragment.setMenuVisibility(boolean)'

void android.support.v4.app.Fragment.setMenuVisibility(boolean)' on a null object reference

提问by Sagar Chavada

The error started to appear only after I started using fragments in the project

只有在我开始在项目中使用片段后才开始出现错误

here is my code..

这是我的代码..

public class MainActivity extends AppCompatActivity {

private Toolbar toolbar;
private ViewPager mPager;
private SlidingTabLayout mTabs;
private MyPagerAdapter adapter;

public static final int product_result = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    toolbar = (Toolbar) findViewById(R.id.app_bar);

    setSupportActionBar(toolbar);
    assert getSupportActionBar() != null;
    getSupportActionBar().setDisplayShowHomeEnabled(true);

    NavigationDrawerFragment navigationDrawerFragment = (NavigationDrawerFragment)
            getSupportFragmentManager().findFragmentById(R.id.fragment_nav_drawer);
    navigationDrawerFragment.setUp(R.id.fragment_nav_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar);

    mPager = (ViewPager) findViewById(R.id.pager);
    adapter = new MyPagerAdapter(getSupportFragmentManager());
    mPager.setAdapter(adapter);

    mTabs = (SlidingTabLayout) findViewById(R.id.tabs);
    mTabs.setDistributeEvenly(true);
    mTabs.setCustomTabView(R.layout.custom_tab_view, R.id.tabText);
    int bgColor = ContextCompat.getColor(this, R.color.colorPrimary);
    mTabs.setBackgroundColor(bgColor);
    mTabs.setSelectedIndicatorColors(ContextCompat.getColor(MainActivity.this, R.color.colorAccent));
    mTabs.invalidate();
    mTabs.setViewPager(mPager);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == R.id.action_settings) {

        return true;
    }
    if (id == R.id.navigate) {
        startActivity(new Intent(this, SubActivity.class));
    }
    if (id == R.id.TabActivity) {
        startActivity(new Intent(this, ActivityUsingTabLibrary.class));
    }
    if (id == R.id.VectorTest) {
        startActivity(new Intent(this, VectorTestActivity.class));
    }
    return super.onOptionsItemSelected(item);
}


class MyPagerAdapter extends FragmentStatePagerAdapter {
    int icons[] = {R.drawable.home, R.drawable.hot_article, R.drawable.dizzy_person};

    public MyPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {

        Fragment fragment = null;
        switch(position){
            case product_result:
                fragment = FragmentProduct.newInstance("","");
                break;
        }
        return fragment;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Drawable drawable = ResourcesCompat.getDrawable(getResources(), icons[position], null);
        drawable.setBounds(0, 0, 36, 36);
        ImageSpan imageSpan = new ImageSpan(drawable);
        SpannableString spannableString = new SpannableString(" ");
        spannableString.setSpan(imageSpan, 0, spannableString.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
        return spannableString;
    }

    @Override
    public int getCount() {
        return 3;
    }
}

}

}

this is my fragment.class where i m passing jsonObject toast.

这是我在其中传递 jsonObject toast 的 fragment.class。

public class FragmentProduct extends Fragment {

public static final String product_url = "http://oasisgroups.com/oApp/product.php";

private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";

private String mParam1;
private String mParam2;
private VolleySingleton volleySingleton;
private ImageLoader imageLoader;
private RequestQueue requestQueue;

public FragmentProduct() {
    // Required empty public constructor
}

public static FragmentProduct newInstance(String param1, String param2) {
    FragmentProduct fragment = new FragmentProduct();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

public static String getRequestUrl(int limit) {
    return product_url + "&limit=" + limit;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }

    volleySingleton = VolleySingleton.getInstance();
    requestQueue = volleySingleton.getmRequestQueue();
    JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, getRequestUrl(10),
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    L.t(getActivity(), response.toString());
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });
    requestQueue.add(request);

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    return inflater.inflate(R.layout.fragment_product, container, false);
}

}

}

stackTrace

堆栈跟踪

02-29 12:10:01.047 17100-17100/com.mydesign.rockstar.materialdesignexample E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mydesign.rockstar.materialdesignexample, PID: 17100
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.Fragment.setMenuVisibility(boolean)' on a null object reference
    at android.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:116)
    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:870)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1086)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:952)
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1474)
    at android.view.View.measure(View.java:18804)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:901)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18804)
    at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:940)
    at android.view.View.measure(View.java:18804)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
    at android.view.View.measure(View.java:18804)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18804)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.view.View.measure(View.java:18804)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18804)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
    at android.view.View.measure(View.java:18804)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2112)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1228)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1464)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1119)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6060)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
    at android.view.Choreographer.doCallbacks(Choreographer.java:670)
    at android.view.Choreographer.doFrame(Choreographer.java:606)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
    at android.os.Handler.handleCallback(Handler.java:746)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5443)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)

i also seen this same problem in this linkand i apply his solution but it wont work for me.. i m still stuck, help me. so check my code and suggest me where what i missing.

我也在这个链接中看到了同样的问题，我应用了他的解决方案，但它对我不起作用..我仍然卡住了，帮帮我。所以检查我的代码并建议我在哪里我错过了什么。

采纳答案by Sagar Chavada

oh yes.. i finally found my mistake.. first of all there is no mistake in my code. everything is right.

哦是的..我终于找到了我的错误..首先我的代码没有错误。一切正常。

i have three tab layout and i m passing only for one tablayout and other two are getting null, so i must have to apply three switch case statement.

我有三个选项卡布局，我只传递一个选项卡布局，其他两个为空，所以我必须应用三个 switch case 语句。

 public Fragment getItem(int position) {

    Fragment fragment = null;
    switch(position){
        case product_result:
            fragment = FragmentProduct.newInstance("","");
            break;
    }
    return fragment;
}

instead

反而

  public Fragment getItem(int num) {
        Fragment fragment = null;
        switch (num) {
            case TAB_PRODUCT_RESULT:
                fragment = FragmentProduct.newInstance("", "");
                break;
            case TAB_SECOND:
                fragment = MyFragment.getInstance(num);
                break;
            case TAB_THIRD:
                fragment = MyFragment.getInstance(num);
                break;
        }
        return fragment;
    }

thats it..

就是这样..

回答by dishan

I think the problem is in the public Fragment getItem(int position)method of your MyPagerAdapter. Your code snippet below is returning nullfragments.

我认为问题出在public Fragment getItem(int position)您的MyPagerAdapter. 您下面的代码片段正在返回null片段。

Fragment fragment = null;
switch(position){
    case product_result:
        fragment = FragmentProduct.newInstance("","");
        break;
    }
return fragment;

You only get a real fragment for the position 0, because product_resultis initialized to 0. In all other cases it returns null. Modify the above snippet of code to always return a fragment instance that is not null.

您只能获得该位置的真实片段0，因为product_result已初始化为0. 在所有其他情况下，它返回 null。修改上面的代码片段以始终返回一个不为空的片段实例。

回答by Sagar Chavada

I had similar problem, I tried to remove null fragment and this cause error. Null check solved problem. Check your fragment transactions. You can't add null fragment.

我有类似的问题，我试图删除空片段，这导致错误。空检查解决了问题。检查您的片段交易。您不能添加空片段。

Fragment fragment = null;
if (fragment != null)
   getSupportFragmentManager().beginTransaction()
           .add(R.id.container, fragment, "id").commit();

回答by Sahil Choudhary

First You Have To Add Adapter in your Activity like this

首先你必须像这样在你的活动中添加适配器

---

---

------- This is Adding number of tab layout according to size of data ------------

------- 这是根据数据大小添加选项卡布局的数量------------

    for (FirstModel firstModel : list_editdata) {
        tabLayout.addTab(tabLayout.newTab().setText(firstModel.getTitle()));
    }

     **/////Set an Adapter** 

SectionAdapter  mSectionAdapter   = new SectionAdapter(getSupportFragmentManager());
    viewPager.setAdapter(mSectionAdapter);

---

---

now Add An Adapter in Activity : I take One Fragments and use in switch case repeatedly This Will automatically regenerate according to your tab layout numbers in Activity

现在在活动中添加一个适配器：我拿一个片段并在开关盒中重复使用这将根据您在活动中的选项卡布局编号自动重新生成

---

---

public class SectionAdapter  extends FragmentPagerAdapter {

    private String[] tabTitles = new String[]{"", "", "", ""};


    public SectionAdapter (FragmentManager fm) {
        super(fm);
    }


    @Override
    public CharSequence getPageTitle(int position) {
        return tabTitles[position];
    }


    @Override
    public Fragment getItem(int position) {


        switch (position) {

            case 0:
                Tab1 tab1 = new Tab1();
                return tab1 ;
            case 1:
                Tab1 tab2 = new Tab1();
                return tab2 ;
            case 2:
                Tab1 tab3 = new Tab1();
                return tab3 ;
            case 3:
                Tab1 tab4 = new Tab1();
                return tab4 ;

        }


        return null;


    }