android - 我如何在 fragment 中添加图像 slider 以及为什么我会收到适配器(适配器)错误？

Question

您好，我正在尝试将 imageslider 添加到我的 Activity 中，但出现错误

正在关注 this tutorial..

在这个位置，我在第 45 行收到此错误:

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

第 45 行是:

sds.setAdapter(adapter);

这是我的actvity.java

public class Sayfalar extends AppCompatActivity implements View.OnClickListener {

    private TabLayout tabLayout;
    private ViewPager viewPager,sds;

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

        sds = (ViewPager) findViewById(R.id.resimler);
        PagerAdapter adapter = new CustomAdapter(Sayfalar.this);
        sds.setAdapter(adapter);


        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);

    }

    public void showDialog (View v){
        MyDialog dialog = new MyDialog();
        dialog.show(getSupportFragmentManager(),"my_dialog");
    }

    private void setupViewPager(ViewPager viewPager) {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFrag(new Fragment1(), "Fragment1");
        adapter.addFrag(new Fragment2(), "Fragment2");
        adapter.addFrag(new Fragment3(), "Fragment3");
        adapter.addFrag(new Fragment4(), "Fragment4");
        adapter.addFrag(new Fragment5(), "Fragment5");
        adapter.addFrag(new Fragment6(), "Fragment6");
        adapter.addFrag(new Fragment7(), "Fragment7");
        adapter.addFrag(new Fragment8(), "Fragment8");
        adapter.addFrag(new Fragment9(), "Fragment9");
        viewPager.setAdapter(adapter);
    }

    public void onClick(View view) {


        }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFrag(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }
    }
}

这是我的activity.xml

<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/popupmenu"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabMode="scrollable"/>
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</android.support.design.widget.CoordinatorLayout>

如果我将这段代码添加到我的 activity.xml 中，我会在所有 fragment 中看到我的图片，但我希望它在一个 fragment 中。

代码如下:

<ImageView
        android:id="@+id/resim"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />

这是 fragment.xml 之一

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Kaynaklar.Agil">


    <android.support.v4.view.ViewPager
        android:id="@+id/resimler"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />
</RelativeLayout>

这里是fragment1.java

public class Fragment1 extends Fragment {

    public Fragment1 () {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment1, container, false);
    }

}

Answer 1

问题出在这里:

sds = (ViewPager) findViewById(R.id.resimler);
PagerAdapter adapter = new CustomAdapter(Sayfalar.this);
sds.setAdapter(adapter);

你的 sayfalar 布局中似乎没有 ViewPager 和 resimler ID，所以 sds 将为 null，然后您将尝试对该 null 引用调用 setAdapter()。

要在 Fragment1 中设置第二个 ViewPager，您可以这样做:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment1, container, false);

    ViewPager sds = (ViewPager) view.findViewById(R.id.resimler);
    // assuming CustomAdapter requires an Activity or Context as a constructor param
    PagerAdapter adapter = new CustomAdapter(getActivity());
    sds.setAdapter(adapter);

    return view;
}