Question

我将如何使用函数中的代码。什么阻止我从函数调用我的回收器视图？这是我得到的错误。

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollVertically()' on a null object reference

提供错误的函数。

void PopulateList(View view)
{

mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);

mRecyclerView.setHasFixedSize(true);

final LinearLayoutManager mLayoutManager = new LinearLayoutManager(this);
mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
//mLayoutManager.isSmoothScrollbarEnabled();
mRecyclerView.setLayoutManager(mLayoutManager);

mAdapter = new RecyclerViewAdapter(EventsData);
mRecyclerView.setAdapter(mAdapter);
}

RecyclerViewAdapter Class

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.TextView;
import android.content.Context;

import com.squareup.picasso.MemoryPolicy;
import com.squareup.picasso.NetworkPolicy;
import com.squareup.picasso.Picasso;

import java.util.ArrayList;

import jp.wasabeef.picasso.transformations.CropCircleTransformation;

/**
 * Created by  on 9/23/2015.
 */
public class RecyclerViewAdapter extends           RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {
private ArrayList<EventsListData> EventsData;
Context context;

public static class ViewHolder extends RecyclerView.ViewHolder
{
    public View view;
    public ViewHolder(View v)
    {
        super(v);
        view = v;
    }
}

public RecyclerViewAdapter(ArrayList<EventsListData> EventsData)
{this.EventsData = EventsData;}



@Override
public RecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

    //ceate a new view
    View v = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.events_list_layout, parent, false);

    //set the view's size, margins, padding and layout paremters;
    ViewHolder vh = new ViewHolder(v);
    return vh;
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {

    // - get elements from your dataset at this position
    // - replace the contenst of the view with that elements

}

    public void setData(int Maxposition)
{

    int position=0;
    TextView txtDisc = (TextView) vh.view.findViewById(R.id.EventDisc);
    TextView txtDistance = (TextView) vh.view.findViewById(R.id.EventsDistance);
    FrameLayout Frame = (FrameLayout) vh.view.findViewById(R.id.EventsFrame);
    ImageView imgView = (ImageView) vh.view.findViewById(R.id.EventsImageView);

    for (int i = 0 ; i <Maxposition ; i++) {
        Picasso.with(this.context).load("file://" + EventsData.get(position).art_work_uri)
                .memoryPolicy(MemoryPolicy.NO_CACHE)
                .networkPolicy(NetworkPolicy.NO_CACHE)
                .centerInside()
                .transform(new CropCircleTransformation())
                        //.resize(200, 200)
                .into(imgView);

        txtDisc.setText(EventsData.get(position).description);
        txtDistance.setText(Float.toString(EventsData.get(position).Distance) + " KM");

        Frame.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                Log.d("XXX","RecyclerView position =");
            }
        });
    }
    position++;
}

@Override
public int getItemCount() { return EventsData.size(); }
}

适配器使用的布局。

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="0.3">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="0.30"
        android:id="@+id/Frame">

        <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="0.98"
            android:id="@+id/EventsFrame">

            <LinearLayout
                android:orientation="vertical"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

                <LinearLayout
                    android:orientation="horizontal"
                    android:layout_width="fill_parent"
                    android:layout_height="0dp"
                    android:layout_weight="0.5"
                    android:paddingLeft="15dp"
                    android:paddingRight="15dp">

                    <TextView
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:textAppearance="?android:attr/textAppearanceLarge"
                        android:id="@+id/EventDisc"
                        android:layout_gravity="center_vertical"
                        android:text="random test text" />
                </LinearLayout>

                <LinearLayout
                    android:orientation="horizontal"
                    android:layout_width="fill_parent"
                    android:layout_height="0dp"
                    android:layout_weight="0.5"
                    android:paddingLeft="15dp">

                    <ImageView
                        android:layout_width="0dp"
                        android:layout_height="wrap_content"
                        android:id="@+id/EventsBlip"
                        android:layout_gravity="center_vertical"
                        android:layout_weight="0.1"
                        android:src="@drawable/point" />

                    <TextView
                        android:layout_width="0dp"
                        android:layout_height="wrap_content"
                        android:textAppearance="?android:attr/textAppearanceMedium"
                        android:text="KM"
                        android:id="@+id/EventsDistance"
                        android:layout_gravity="center_vertical"
                        android:layout_weight="0.9"
                        android:paddingLeft="10dp"
                        android:layout_marginRight="15dp" />

                </LinearLayout>

            </LinearLayout>
        </FrameLayout>

        <FrameLayout
            android:layout_width="fill_parent"
            android:layout_height="0dp"
            android:layout_gravity="center_horizontal"
            android:layout_weight="0.02"
            android:background="#888888">

        </FrameLayout>

    </LinearLayout>

    <ImageView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/EventsImageView" />
</FrameLayout>

按要求提供LogCat ......

 java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollVertically()' on a null object reference
        at android.support.v7.widget.RecyclerView.computeVerticalScrollRange(RecyclerView.java:1545)
        at android.view.View.onDrawScrollBars(View.java:12866)
        at android.view.View.draw(View.java:15154)
        at android.support.v7.widget.RecyclerView.draw(RecyclerView.java:3037)
        at android.view.View.updateDisplayListIfDirty(View.java:14082)
        at android.view.View.getDisplayList(View.java:14105)
        at android.view.View.draw(View.java:14872)
        at android.view.ViewGroup.drawChild(ViewGroup.java:3404)
        at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
        at android.view.View.updateDisplayListIfDirty(View.java:14077)
        at android.view.View.getDisplayList(View.java:14105)
        at android.view.View.draw(View.java:14872)
        at android.view.ViewGroup.drawChild(ViewGroup.java:3404)
        at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
        at android.view.View.updateDisplayListIfDirty(View.java:14077)
        at android.view.View.getDisplayList(View.java:14105)
        at android.view.View.draw(View.java:14872)
        at android.view.ViewGroup.drawChild(ViewGroup.java:3404)
        at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
        at android.view.View.updateDisplayListIfDirty(View.java:14077)
        at android.view.View.getDisplayList(View.java:14105)
        at android.view.View.draw(View.java:14872)
        at android.view.ViewGroup.drawChild(ViewGroup.java:3404)
        at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
        at android.view.View.updateDisplayListIfDirty(View.java:14077)
        at android.view.View.getDisplayList(View.java:14105)
        at android.view.View.draw(View.java:14872)
        at android.view.ViewGroup.drawChild(ViewGroup.java:3404)
        at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
        at android.view.View.updateDisplayListIfDirty(View.java:14077)
        at android.view.View.getDisplayList(View.java:14105)
        at android.view.View.draw(View.java:14872)
        at android.view.ViewGroup.drawChild(ViewGroup.java:3404)
        at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
        at android.view.View.draw(View.java:15151)
        at android.widget.FrameLayout.draw(FrameLayout.java:592)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2657)
        at android.view.View.updateDisplayListIfDirty(View.java:14082)
        at android.view.View.getDisplayList(View.java:14105)
        at android.view.ThreadedRenderer.updateViewTreeDisplayList(ThreadedRenderer.java:266)
        at android.view.ThreadedRenderer.updateRootDisplayList(ThreadedRenderer.java:272)
        at android.view.ThreadedRenderer.draw(ThreadedRenderer.java:311)
        at android.view.ViewRootImpl.draw(ViewRootImpl.java:2528)
        at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2366)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1997)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1077)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5845)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:550)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5274)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:909)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:704)

请注意！我注意到如果我注释掉与RecyclerView有关的一切，它仍然会发生。所以我在布局XML中注释掉它并且它有效。

<  android.support.v7.widget.RecyclerView
        android:id="@+id/my_recycler_view"
        android:scrollbars="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
 />

所以我在我的RecyclerViewAdapter类中添加了一个函数，但不太确定它是否可行。因为我实际上无法从我的对象中调用它而我无法弄清楚为什么？所以我真的不知道这是否有效。为什么我打电话给它？

public void setData(int Maxposition)
{

    int position=0;
    TextView txtDisc = (TextView) vh.view.findViewById(R.id.EventDisc);
    TextView txtDistance = (TextView) vh.view.findViewById(R.id.EventsDistance);
    FrameLayout Frame = (FrameLayout) vh.view.findViewById(R.id.EventsFrame);
    ImageView imgView = (ImageView) vh.view.findViewById(R.id.EventsImageView);

    for (int i = 0 ; i <Maxposition ; i++) {
        Picasso.with(this.context).load("file://" + EventsData.get(position).art_work_uri)
                .memoryPolicy(MemoryPolicy.NO_CACHE)
                .networkPolicy(NetworkPolicy.NO_CACHE)
                .centerInside()
                .transform(new CropCircleTransformation())
                        //.resize(200, 200)
                .into(imgView);

        txtDisc.setText(EventsData.get(position).description);
        txtDistance.setText(Float.toString(EventsData.get(position).Distance) + " KM");

        Frame.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                Log.d("XXX","RecyclerView position =");
            }
        });
    }
    position++;
}

Answer 1

好像你打电话给PopulateList太晚了（或者根本没有）。确保在创建视图后尽快调用它，因此如果您使用的是Activity，则必须在PopulateList()中调用onCreate，如果您使用的是片段，则必须在onCreateView中调用。

您不必立即设置适配器/数据，但必须在RecyclerView显示之前设置布局管理器。

从函数中断

1 个答案: