Question

我很难在其他对象中获取OBJECT实例的值。我想要的只是在评论中获得＆＃34; Email＆＃34;（凭据）的价值。它在我的CustomListViewAdapter中给了我NullPointerException。

这是我的代码：评论对象：

public class Comments implements Parcelable {
public int _id;
public String currentTimeStamp;
public String commentContent;
public LocationsData locationsData;
public Credentials credentials;

public Comments() {
    super();
}

public Comments( String currentTimeStamp, String commentContent, LocationsData locationsData, Credentials credentials) {
    this.currentTimeStamp = currentTimeStamp;
    this.commentContent = commentContent;
    this.locationsData = locationsData;
    this.credentials = credentials;
}

public int get_id() {
    return _id;
}

public void set_id(int _id) {
    this._id = _id;
}

public String getCurrentTimeStamp() {
    return currentTimeStamp;
}

public void setCurrentTimeStamp(String currentTimeStamp) {
    this.currentTimeStamp = currentTimeStamp;
}

public String getCommentContent() {
    return commentContent;
}

public void setCommentContent(String commentContent) {
    this.commentContent = commentContent;
}

public LocationsData getLocationsData() {
    return locationsData;
}

public void setLocationsData(LocationsData locationsData) {
    this.locationsData = locationsData;
}

public Credentials getCredentials() {
    return credentials;
}

public void setCredentials(Credentials credentials) {
    this.credentials = credentials;
}

public static Creator<Comments> getCREATOR() {
    return CREATOR;
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeInt(this._id);
    dest.writeString(this.currentTimeStamp);
    dest.writeString(this.commentContent);
    dest.writeParcelable(this.locationsData, flags);
    dest.writeParcelable(this.credentials, flags);
}

protected Comments(Parcel in) {
    this._id = in.readInt();
    this.currentTimeStamp = in.readString();
    this.commentContent = in.readString();
    this.locationsData = in.readParcelable(LocationsData.class.getClassLoader());
    this.credentials = in.readParcelable(Credentials.class.getClassLoader());
}

public static final Parcelable.Creator<Comments> CREATOR = new Parcelable.Creator<Comments>() {
    @Override
    public Comments createFromParcel(Parcel source) {
        return new Comments(source);
    }

    @Override
    public Comments[] newArray(int size) {
        return new Comments[size];
    }
};

}

这是我的凭证对象类

public class Credentials implements Parcelable {
public long _id;
public String password;
public String email;

public Credentials() {

}

public Credentials(String email,String password) {
    this.password=password;
    this.email= email;
}

public Credentials(long id,String email,String password) {
    this._id=id;
    this.email=email;
    this.password=password;
}

public long get_id() {
    return _id;
}

public void set_id(long _id) {
    this._id = _id;
}

public String getPassword() {
    return password;
}

public void setPassword(String password) {
    this.password = password;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeLong(this._id);
    dest.writeString(this.password);
    dest.writeString(this.email);
}

protected Credentials(Parcel in) {
    this._id = in.readInt();
    this.password = in.readString();
    this.email = in.readString();
}

public static final Parcelable.Creator<Credentials> CREATOR = new Parcelable.Creator<Credentials>() {
    @Override
    public Credentials createFromParcel(Parcel source) {
        return new Credentials(source);
    }

    @Override
    public Credentials[] newArray(int size) {
        return new Credentials[size];
    }
};

}

我的CustomListViewAdapter类：

public class CommentsAdapter extends ArrayAdapter<Comments>{

ArrayList<Comments> commentses;
Context ctx;
Credentials credentials= new Credentials();


public CommentsAdapter(Context context, int resource) {
    super(context, resource);
    this.ctx=context;
}

public CommentsAdapter(Context context, int resource, ArrayList<Comments> commentsArrayList) {
    super(context, resource,commentsArrayList);
    this.commentses=commentsArrayList;
    this.ctx=context;
    this.credentials=credentials;
}

@NonNull
@Override
public View getView(int position, View convertView, ViewGroup parent) {

    Comments  comments= getItem(position);
    LayoutInflater inflater= LayoutInflater.from(ctx);
    CommentsViewholder holder;

    if (convertView == null) {
        holder= new CommentsViewholder();
        convertView= inflater.inflate(R.layout.customcomment_layout,parent,false);
        holder.email= (TextView)convertView.findViewById(R.id.customlistview_username);
        holder.commentContent= (TextView)convertView.findViewById(R.id.customlistview_commentcontent);
        holder.timeStamp= (TextView)convertView.findViewById(R.id.customlistview_timestamp);
    }else {
        holder=(CommentsViewholder)convertView.getTag();
    }

    credentials.getEmail();
    comments.setCredentials(credentials);

    holder.email.setText(comments.getCredentials().getEmail()); //-----NullPointerException

    holder.commentContent.setText(comments.getCommentContent());
    holder.timeStamp.setText(comments.getCurrentTimeStamp());
    return convertView;
}

private static class CommentsViewholder{
    TextView email;
    TextView commentContent;
    TextView timeStamp;
}

}

这是NPE遇到CustomAdapter中的哪些点

holder.email.setText（comments.getCredentials（）getEmail（））; // -----的NullPointerException

FATAL EXCEPTION: main
    Process: onetown.otop.onetownoneproduct, PID: 29669
    java.lang.NullPointerException: Attempt to read from field 'android.widget.TextView onetown.otop.onetownoneproduct.Classes.CommentsAdapter$CommentsViewholder.email' on a null object reference
    at onetown.otop.onetownoneproduct.Classes.CommentsAdapter.getView(CommentsAdapter.java:61)
    at android.widget.AbsListView.obtainView(AbsListView.java:2467)
    at android.widget.ListView.onMeasure(ListView.java:1166)
    at android.view.View.measure(View.java:17915)
    at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1286)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:465)
    at android.widget.ScrollView.onMeasure(ScrollView.java:342)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5698)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1692)
    at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1244)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:631)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5698)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1692)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:760)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5698)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:465)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5698)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1692)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:760)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5698)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:465)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5698)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1692)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:760)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5698)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:465)
    at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2731)
    at android.view.View.measure(View.java:17915)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2413)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2105)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1293)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6599)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:800)
    at android.view.Choreographer.doCallbacks(Choreographer.java:603)
    at android.view.Choreographer.doFrame(Choreographer.java:572)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:786)
    at android.os.Handler.handleCallback(Handler.java:815)
    at android.os.Handler.dispatchMessage(Handler.java:104)
    at android.os.Looper.loop(Looper.java:194)
    at android.app.ActivityThread.main(ActivityThread.java:5637)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
    at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:114)

Answer 1

您的崩溃不是由comments.getCredentials().getEmail()引起的。

问题是您没有在convertedView上设置标记。

if (convertView == null) {
        holder= new CommentsViewholder();
        convertView= inflater.inflate(R.layout.customcomment_layout,parent,false);
        holder.email= (TextView)convertView.findViewById(R.id.customlistview_username);
        holder.commentContent= (TextView)convertView.findViewById(R.id.customlistview_commentcontent);
        holder.timeStamp= (TextView)convertView.findViewById(R.id.customlistview_timestamp);
        //here you have to set the holder on the convertView.
        convertView.setTag(holder);
} else {
        holder=(CommentsViewholder)convertView.getTag();
}

在您的实现中，行convertView.getTag()将返回null，然后当您调用holder.email时，您将获得NPE。

如何获取其他类实例值？

1 个答案: