java - Android Studio无法在Fragment类和Thread之间传递TextView对象

Question

错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

在线:

olxLoadingFragment.pricesTextView.setText("some text");

我有一个名为 OLXLoadingFragment 的 Fragment 类，它有一个嵌套在 ScrollView 中的 TextView。我基本上想在 OLXThread 中动态更新 TextView 的文本，但无法将该 TextView 对象传递给 OLXThread 本身。以下是可以帮助您的代码部分:

OLXLoadingFragment 类:

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ScrollView;
import android.widget.TextView;

import java.io.Serializable;

public class OLXLoadingFragment extends Fragment {
    public static View OLXLoadingFragmentView;
    public static ScrollView scrollViewPrices;
    public static TextView pricesTextView;
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        OLXLoadingFragmentView = inflater.inflate(R.layout.fragment_olx_loading, container, false);
        scrollViewPrices = OLXLoadingFragmentView.findViewById(R.id.olx_scroller);
        pricesTextView = OLXLoadingFragmentView.findViewById(R.id.olx_prices_text);
        return inflater.inflate(R.layout.fragment_olx_loading, container, false);
    }
}

OLXThread 类:

import android.app.Activity;
import android.app.Application;
import android.content.Context;
import android.content.Intent;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.widget.ScrollView;
import android.widget.TextView;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;
import org.w3c.dom.Text;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Scanner;

import static android.app.PendingIntent.getActivity;

public class OLXThread extends Thread {
    public static double fullSum = 0.0d;
    public static ArrayList<String> pricesPerPage = new ArrayList<String>();
    public static ArrayList<String> pricesPerPage2 = new ArrayList<String>();
    public static ArrayList<String> prices = new ArrayList<String>();
    public static String toSearch;
    public static TextView olxpricesView;
    public static Context context;
    public OLXThread(String toSearch) {
        this.toSearch = toSearch;
    }

    public void run() {
        //SET SOME TEXT TO TEXTVIEW HERE
        OLXLoadingFragment olxLoadingFragment = new OLXLoadingFragment();
        olxLoadingFragment.pricesTextView.setText("some text"); //<- DOESN'T WORK!
    }

OLXLoadingFragment xml 布局:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent" android:layout_height="match_parent">

    <ImageView
            android:id="@+id/imageView2"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@drawable/rectangle"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.82" />

    <TextView
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:gravity="center"
            android:text="@string/olx_loading_engl_text"
            android:textColor="@color/limegreen"
            android:textSize="30sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="1.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.82" />

    <ImageView
            android:id="@+id/imageView6"
            android:layout_width="287dp"
            android:layout_height="284dp"
            android:src="@drawable/rectangle"
            app:layout_constraintBottom_toBottomOf="@+id/olx_scroller"
            app:layout_constraintEnd_toEndOf="@+id/olx_scroller"
            app:layout_constraintStart_toStartOf="@+id/olx_scroller"
            app:layout_constraintTop_toTopOf="@+id/olx_scroller" />

    <ScrollView
            android:id="@+id/olx_scroller"
            android:layout_width="287dp"
            android:layout_height="284dp"
            android:layout_marginBottom="36dp"
            android:fillViewport="true"
            android:scrollbars="vertical"
            app:layout_constraintBottom_toTopOf="@+id/imageView2"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent">

        <TextView
                android:id="@+id/olx_prices_text"
                android:text="neki tekst"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:layout_weight="1.0"

                />
    </ScrollView>
</android.support.constraint.ConstraintLayout>

请帮忙!

Answer 1

当你调用priceTextView.setText()方法时，Fragment的OnCreateView方法还没有被调用，所以priceTextView仍然为空，因为你只在onCreateView方法上设置了它的值。

在调用任何方法之前，您应该确保 ratesTextView 不为 null。

另请注意，唯一可以接触 View 的线程是 Ui 线程，因此即使您的 TextView 不为 null，您也无法在其他线程中修改它的属性