java - 如何解决android空指针异常问题？

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 4 年前。

为什么我会收到 java.lang.NullPointerException？

package com.example.vinhpt.listviewcoban_dulieucodinh;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    ListView lvThu;
    String []arrThu;
    ArrayAdapter<String>adapterThu;


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

    private void addControls() {
        arrThu = getResources().getStringArray(R.array.arrThu);
        adapterThu = new ArrayAdapter<String>(
                MainActivity.this,
                android.R.layout.simple_list_item_1,
                arrThu
        );
        lvThu = (ListView) findViewById(R.id.lvThu);
        lvThu.setAdapter(adapterThu);

    }

    private void addEvents() {
        lvThu.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(MainActivity.this, arrThu[position],Toast.LENGTH_LONG).show();
            }
        });
    }    
}

Answer 1

您正在将事件分配给空 Controller !!!
你应该首先调用 addControllers 然后调用 addEvents