相关疑难解决方法(0)

我尝试了下面提到的这个代码,但在运行时遇到崩溃.发生的错误是Android运行时:

致命异常:主要进程:com.root.specialbridge,PID:17706 kotlin.KotlinNullPointerException at com.root.specialbridge.fragments.profile_fragment.WallFragments.initializeView(WallFragments.kt:49)

class WallFragments : Fragment(){

private var wallAdapter: WallAdapter? = null
private var wall_recycler: RecyclerView? = null
private val wallArrayList: ArrayList<Wall>? = null
private var mainlayout: LinearLayout? = null
private var no_result_found_layout: RelativeLayout? = null
private var userProfileWallInterface: UserProfileWallInterface? = null
internal var wallActivityBeanse: MutableList<WallActivityBeans> = ArrayList()

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val view = inflater!!.inflate(R.layout.wall_fragments, container, false)
    userProfileWallInterface = UserProfileWallPresentation(activity, this)
    initializeView()
    wallAdapter = WallAdapter(activity, wallActivityBeanse)
    wall_recycler!!.adapter = wallAdapter

    return …

我一直在读很多片段.发现其他人在检索片段视图时遇到问题,因为总是返回null,但没有答案解决了我的问题.我要做的是创建一个图库.我有一个包含图像视图的片段.为了显示片段,我使用了android.support.v4.view.ViewPager.而喂ViewPager我使用一个android.support.v4.app.FragmentStatePagerAdapter.

问题是,当所有内容都构建并显示图像时,我想将当前显示的图像保存到磁盘.所以我需要得到当前的片段imageview,但我不能,因为fragment.getView()总是为null,与片段相关的活动也是null,我无法弄清楚它为什么.这里有一些代码,看看是否有人可以帮助:

这是我的片段:

public class ImageViewURLFragment extends Fragment 
{
    String _url;

    @Override
    public View onCreateView(LayoutInflater inflater,
            ViewGroup container, Bundle savedInstanceState) 
    {
        // The last two arguments ensure LayoutParams are inflated
        // properly.
        View rootView = new ImageViewURL(getActivity(), _url);

        return rootView;
    }

    public void setImageURL(String imgURL)
    {
        _url=imgURL;
    }
}

这是我的适配器:

public class ImageViewURLCustomAdapter extends FragmentStatePagerAdapter 
{
    List<String> _urls=new ArrayList<String>();

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

    @Override
    public Fragment getItem(int i) 
    {
        ImageViewURLFragment fragment = new ImageViewURLFragment(); …

我已经在Google Play中安装了一个应用程序,在我升级Android Studio之前完全没问题.必须修改build.gradle以便可以编译项目以下是我更改的内容:

dependencies {
    compile fileTree(dir: 'libs', include: '*.jar')
    compile 'com.android.support:appcompat-v7:21.0.0'
    compile 'com.google.android.gms:play-services:6+'
    compile 'com.android.support:support-v4:+'
}

唯一的变化是com.android.support:appcompat-v7:+,它更改为com.android.support:appcompat-v7:21.0.0.

我的问题是.findViewById(R.id.tabhost)总是返回null,以便应用程序崩溃.这是我的布局文件:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.app.FragmentTabHost xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/tabhost"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

我的java代码:

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTabHost;

public class MenuLeftFragment extends Fragment {
    private FragmentTabHost mFragmentTabHost;

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        mView = getView();
        if (mView != null) {
            mFragmentTabHost = (FragmentTabHost) mView
                    .findViewById(R.id.tabhost);

任何的想法？谢谢.