尝试在空对象引用上调用虚拟方法'void android.widget.TextView.setTextColor（int）'[重复]

Question

此问题已经在这里有了答案：

What is a NullPointerException, and how do I fix it?（12个答案）

关闭41秒前。

我尝试更改ListView的文本颜色，但收到错误。

我尝试使用所有类型的方法来更改文本颜色，例如Color.colorname或getColor（），但一次又一次收到相同的错误。

代码可以完美编译，没有错误，但是应用程序在启动时崩溃。

这是我的代码：-

package com.example.newsupdates;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import android.content.res.ColorStateList;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    ListView listView;
    ArrayList<String> titles = new ArrayList<>();
    ArrayAdapter<String> arrayAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listView = findViewById(R.id.listView);
        titles.add("Surprise Mother Fucker");
        arrayAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,titles){
            @NonNull
            @Override
            public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {

                TextView textView = findViewById(android.R.id.text1);

                textView.setTextColor(Color.BLACK);

                return super.getView(position, convertView, parent);
            }
        };

        listView.setAdapter(arrayAdapter);
    }
}

这里是错误日志的详细信息：-

Process: com.example.newsupdates, PID: 1558
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setTextColor(int)' on a null object reference
        at com.example.newsupdates.MainActivity$1.getView(MainActivity.java:46)
        at android.widget.AbsListView.obtainView(AbsListView.java:2372)
        at android.widget.ListView.makeAndAddView(ListView.java:2052)
        at android.widget.ListView.fillDown(ListView.java:786)
        at android.widget.ListView.fillFromTop(ListView.java:847)
        at android.widget.ListView.layoutChildren(ListView.java:1826)
        at android.widget.AbsListView.onLayout(AbsListView.java:2171)
        at android.view.View.layout(View.java:19590)
        at android.view.ViewGroup.layout(ViewGroup.java:6053)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
        at android.view.View.layout(View.java:19590)
        at android.view.ViewGroup.layout(ViewGroup.java:6053)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:19590)
        at android.view.ViewGroup.layout(ViewGroup.java:6053)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1791)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1635)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1544)
        at android.view.View.layout(View.java:19590)
        at android.view.ViewGroup.layout(ViewGroup.java:6053)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:19590)
        at android.view.ViewGroup.layout(ViewGroup.java:6053)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1791)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1635)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1544)
        at android.view.View.layout(View.java:19590)
        at android.view.ViewGroup.layout(ViewGroup.java:6053)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:758)
        at android.view.View.layout(View.java:19590)
        at android.view.ViewGroup.layout(ViewGroup.java:6053)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2484)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2200)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1386)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6733)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
        at android.view.Choreographer.doCallbacks(Choreographer.java:723)
        at android.view.Choreographer.doFrame(Choreographer.java:658)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
        at android.os.Handler.handleCallback(Handler.java:789)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6541)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

您应该在View's之前传递findViewById

对象

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

                TextView textView = convertView.findViewById(android.R.id.text1);
                textView.setTextColor(Color.BLACK);
                return super.getView(position, convertView, parent);
            }
        };