如何获取其他类实例值？

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“电子邮件”（凭证）的价值。它在我的CustomListViewAdapter中给了我NullPointerException。如何获取其他类实例值？

这里是我的代码：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]; 
    } 
};

}

这里是我的凭据对象类

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; 
}

}

这里的NPE我遇到其中CustomAdapter内部指向

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

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)

来源

2016-12-19 PhilipJ

发布您的错误日志。删除静态关键字frmo CommentsViewholder。 – Noorul

完成更新先生。 – PhilipJ

*删除静态关键字frmo CommentsViewholder *为什么？ ... – Selvin

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

问题是您没有在convertedView上设置标签。

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，当你调用holder.email你NPE行convertView.getTag()将返回null，然后。

来源

2016-12-19 15:42:55 danypata

@selvin这是让标签没有设置标签。该标签没有设置在任何地方。 – danypata

是的..需要设置setTag（convertview）如果条件块 – Onkar

Sir Selvin，你救了我的一天！我把convertView.setTag（持有人）后，它现在显示列表视图。非常感谢！非常感谢！ – PhilipJ

如何获取其他类实例值？

回答

相关问题