Question

我不知道如何解释这个，所以我在Youtube.上传了一段视频当我添加页面时，一切正常。如果我从列表的末尾开始并逐步移动到第一页，也删除页面工作，但如果我删除0之间和之后的某处我添加页面，我得到一个空白页面。片段已创建但视图不是。

我的代码有问题吗？是的，我看到this问题，返回POSITION_NONE不是一个选项，因为我正在处理的应用程序从web下载内容并将其显示在listview中，因此每次用户删除页面时重新创建片段都不是很有效。

Button click:            Result:

Add page                 [Fragment 1]
Add page                 [Fragment 1][Fragment 2]
Add page                 [Fragment 1][Fragment 2][Fragment 3]
remove page(position2)   [Fragment 1][Fragment 2]
remove page(position1)   [Fragment 1]
Add page                 [Fragment 1][Fragment 2]
remove page(position1)   [Fragment 1]
remove page(position0)    ---No pages---


Add page                 [Fragment 0]
Add page                 [Fragment 0][Fragment 1]
Add page                 [Fragment 0][Fragment 1][Fragment 2]
add page                 [Fragment 0][Fragment 1][Fragment 2][fragment 3]
remove page(position2)   [Fragment 0][Fragment 1][Fragment 3]
add page                 [Fragment 0][Fragment 1][Fragment 3][Blank page]
remove page(position0)   [Fragment 1][Fragment 3][Fragment 3][Blank page]

MainActivity.class

    public class MainActivity extends FragmentActivity {
    private static final String TAG = "MainActivity";
    private ViewPager mViewpager;
    private ArrayList<Fragment> fragmentslist;
    private SectionsPagerAdapter mPagerAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fragmentslist = new ArrayList<Fragment>();
        mPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
        mViewpager = (ViewPager)findViewById(R.id.pager);
        mViewpager.setAdapter(mPagerAdapter);
        mViewpager.setOffscreenPageLimit(4);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected (MenuItem item){
        switch(item.getItemId()){
        case R.id.menu_add_page:
            Bundle bundle = new Bundle();
            bundle.putInt("Position", fragmentslist.size());
            fragment frag = new fragment();
            frag.setArguments(bundle);
            fragmentslist.add(frag);
            mPagerAdapter.notifyDataSetChanged();
            mViewpager.setCurrentItem(fragmentslist.indexOf(frag));
            Log.i(TAG, "Add fragment");
            break;
        case R.id.menu_remove_page:
            if(fragmentslist.size() > 0){
                mPagerAdapter.removeItem(mViewpager.getCurrentItem());
            }
            Log.i(TAG, "Removing page " + mViewpager.getCurrentItem());
            break;
        }
        return true;
    }


    public class SectionsPagerAdapter extends FragmentPagerAdapter {

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

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

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

        @Override
        public int getItemPosition(Object object){
            int index = fragmentslist.indexOf(object);
            if(index != -1){
                Log.i(TAG, "Position: " + index);
                return index;
            }
            else{
                Log.i(TAG, "POSITION_NONE");
                return POSITION_NONE;
            }
        }

        public void removeItem(int position){
            Fragment fragment = (Fragment)fragmentslist.get(position);
            getSupportFragmentManager().beginTransaction().remove(fragment).commit();
            fragmentslist.remove(position);
            notifyDataSetChanged();
        }

    }


    public static class fragment extends Fragment{
        private String colors[] = {"#FF0000", "#00FF00", "#FFFF00", "#FF6600"};

        public View onCreateView(LayoutInflater inflater, ViewGroup root, Bundle savedInstanceState){
            View mView = inflater.inflate(R.layout.fragment_layout, null);
            RelativeLayout layout = (RelativeLayout)mView.findViewById(R.id.relativelayout);
            TextView text = (TextView)mView.findViewById(R.id.textView1);

            int position = this.getArguments().getInt("Position");
            text.setText("Page: " + position);
            layout.setBackgroundColor(Color.parseColor(colors[position]));
            Log.i("fragment", "Page: " + position + " view created");
            return mView;
        }
    }

}

activity_main.xml中：

<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">

<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</android.support.v4.view.ViewPager>

fragment_layout.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent" 
android:id="@+id/relativelayout">

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:text="Large Text"
    android:textSize="40sp" />

Answer 1

在添加或删除列表中的项目之前，请尝试执行mViewpager.setAdapter（null）。然后，将适配器设置回mPagerAdapter。似乎ViewPager不是为处理插入或删除而设计的，除了从列表末尾开始。

我有可能对您有用的示例代码。看看ViewPager sample。

Android viewpager：添加/删除页面时的奇怪错误

1 个答案: