Android 在“其他活动”中使用“打开”按钮单击侦听器时出错

我是Android编程新手。如果有人能帮我，我会很高兴的

在SelectCity活动中使用提交按钮时出错

这是我的主要活动

package com.example.dell.myop;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;


import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;

import com.example.dell.myop.R;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.widget.TextView;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;


import com.example.dell.myop.fragments.OneFragment;

import com.example.dell.myop.fragments.ThreeFragment;
import com.example.dell.myop.fragments.TwoFragment;

public class MainActivity extends AppCompatActivity {


    private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;
    public static SharedPreferences prefs;


@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);


        setContentView(R.layout.activity_main);

            toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);

            getSupportActionBar().setDisplayHomeAsUpEnabled(true);

            viewPager = (ViewPager) findViewById(R.id.viewpager);
            setupViewPager(viewPager);

            tabLayout = (TabLayout) findViewById(R.id.tabs);
            tabLayout.setupWithViewPager(viewPager);
            prefs = getSharedPreferences("PREFERENCES",MODE_PRIVATE);
        getSharedPreferences("PREFERENCE", MODE_PRIVATE).edit()
                .putBoolean("isFirstRun", true).commit();

     Boolean isFirstRun = prefs.getBoolean("RUN",true);


        if (isFirstRun) {
            //show start activity
            Intent intent = new Intent(MainActivity.this,SelectCity.class);
            startActivity(intent);


            Toast.makeText(MainActivity.this, "First Run", Toast.LENGTH_LONG)
                    .show();

        }




        }

private void setupViewPager(ViewPager viewPager) {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new OneFragment(), "Today");
        adapter.addFragment(new TwoFragment(), "Tomorrow");
        adapter.addFragment(new ThreeFragment(), "Day After");
        viewPager.setAdapter(adapter);
    }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFragment(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }
    }
}

---

您需要放置

super.oncreate（）

和setcontentview（。。。 在selectCity中，首先调用onCreate方法；）

如下

@Override
protected void onCreate(Bundle savedInstanceState) {

   super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_select_city);
    editText = (EditText)findViewById(R.id.cityName);
    submitButton = (Button)findViewById(R.id.submitButton);
   submitButton.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
          Log.i("edit test value",editText.toString());

        }
    });    
}

---

添加错误的日志

@Override
protected void onCreate(Bundle savedInstanceState) {

   super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_select_city);
    editText = (EditText)findViewById(R.id.cityName);
    submitButton = (Button)findViewById(R.id.submitButton);
   submitButton.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
          Log.i("edit test value",editText.toString());

        }
    });    
}