Question

我已经使用这个网站多年了，但这是我第一次无法找到问题的答案。我正在关注一个在线教程，以便从RSS源向我的应用添加图像缩略图。我一直在从我的convertView实例化中遇到一个NULL指针错误，但它实际上是如何实例化教程的，所以我不明白为什么会这样。

public class PostItemAdapter extends ArrayAdapter<PostData> {
    private Activity myContext;
    private ArrayList<PostData> datas;
    private String[] imageURLArray;
    LayoutInflater inflater;

    static class ViewHolder {
        TextView postTitleView;
        TextView postDateView;
        ImageView postThumbView;
        String postThumbViewURL;
        Bitmap bitmap;

    }

    public PostItemAdapter(Context context, int textViewResourceId,
                           ArrayList<PostData> objects) {
        super(context, textViewResourceId, objects);
        // TODO Auto-generated constructor stub
        myContext = (Activity) context;
        datas = objects;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.postitem, null);

            viewHolder = new ViewHolder();
            viewHolder.postThumbView = (ImageView) convertView.findViewById(R.id.postThumb);
            viewHolder.postTitleView = (TextView) convertView.findViewById(R.id.postTitleLabel);
            viewHolder.postDateView = (TextView) convertView.findViewById(R.id.postDateLabel);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        PostData post = datas.get(position);
        if (post.postThumbUrl != null) {
            viewHolder.postThumbViewURL = post.postThumbUrl;
            new DownloadImageTask().execute(viewHolder);
        } else {
            viewHolder.postThumbView.setImageResource(R.drawable.ic_action_event);
        }

        viewHolder.postTitleView.setText(post.postTitle);
        viewHolder.postDateView.setText(post.postDate);
        new DownloadImageTask().execute(viewHolder);
        return convertView;
    }
}

堆栈追踪：

04-24 13:32:12.748    7335-7335/com.chuckfranklin.chuckfranklinlaw E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.chuckfranklin.chuckfranklinlaw, PID: 7335
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup)' on a null object reference
            at com.chuckfranklin.chuckfranklinlaw.PostItemAdapter.getView(PostItemAdapter.java:56)
            at android.widget.AbsListView.obtainView(AbsListView.java:2825)
            at android.widget.ListView.makeAndAddView(ListView.java:1884)
            at android.widget.ListView.fillDown(ListView.java:713)
            at android.widget.ListView.fillFromTop(ListView.java:779)
            at android.widget.ListView.layoutChildren(ListView.java:1679)
            at android.widget.AbsListView.onLayout(AbsListView.java:2629)
            at android.view.View.layout(View.java:16694)
            at android.view.ViewGroup.layout(ViewGroup.java:5328)
            at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1077)
            at android.view.View.layout(View.java:16694)
            at android.view.ViewGroup.layout(ViewGroup.java:5328)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:16694)
            at android.view.ViewGroup.layout(ViewGroup.java:5328)
            at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:502)
            at android.view.View.layout(View.java:16694)
            at android.view.ViewGroup.layout(ViewGroup.java:5328)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:16694)
            at android.view.ViewGroup.layout(ViewGroup.java:5328)
            at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1702)
            at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1556)
            at android.widget.LinearLayout.onLayout(LinearLayout.java:1465)
            at android.view.View.layout(View.java:16694)
            at android.view.ViewGroup.layout(ViewGroup.java:5328)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
            at android.view.View.layout(View.java:16694)
            at android.view.ViewGroup.layout(ViewGroup.java:5328)
            at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2321)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2034)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1191)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6641)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:777)
            at android.view.Choreographer.doCallbacks(Choreographer.java:590)
            at android.view.Choreographer.doFrame(Choreographer.java:560)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:763)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:145)
            at android.app.ActivityThread.main(ActivityThread.java:5942)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

Answer 1

与日志一样：

NullPointerException：尝试调用虚方法＆＃39; android.view.View android.view.LayoutInflater.inflate

显然，使用inflate的非初始化对象调用LayoutInflater方法。将其初始化为：

inflater = (LayoutInflater) 
               myContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

Answer 2

您忘记初始化inflater。由于您在构造函数中已获得Context，因此您可以通过以下方式执行此操作：

inflater = LayoutInflater.from(context);

当然，它应该添加到构造函数中，而不是getView。

Answer 3

您无法在不初始化的情况下访问会员。

public PostItemAdapter(Context context, int textViewResourceId, ArrayList<PostData> objects) {
    super(context, textViewResourceId, objects);
    myContext = (Activity) context;
    inflater = Layourinflater.from(context);
    datas = objects;
}

Answer 4

您的inflater永远不会被初始化，因此您会收到此错误。

使用此

inflater = LayoutInflater.from(context);

Answer 5

在初始化convertview之前，在getView（）中添加一行代码，如下所示：

if (convertView == null) {
 // This a new view we inflate the new layout              
 LayoutInflater inflater = (LayoutInflater) 
 context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
 convertView = inflater.inflate(R.layout.postitem, null);
}

Android Null指针问题

5 个答案: