Java 使用edittext时出现NullPointer异常

我想将此van值存储在本地主机数据库中，但不幸的是它已停止工作，请帮助

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

import android.app.ActionBar;
import android.content.Intent;
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;

public class UserOptions extends OnscreenActivity {
    protected Button subButton;
     EditText vNumber;
     InputStream is=null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActionBar actionbar = getActionBar();
        actionbar.hide();
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
                .permitAll().build();
        StrictMode.setThreadPolicy(policy);
        vNumber = (EditText)findViewById(R.id.editText1);

        setContentView(R.layout.activity_user_options);
        Spinner Schoolspin = (Spinner) findViewById(R.id.spinner1);
        // Create an ArrayAdapter using the string array and a default spinner
        // layout
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this, R.array.school_names,
                android.R.layout.simple_spinner_item);

        // Specify the layout to use when the list of choices appears
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        // Apply the adapter to the spinner
        Schoolspin.setAdapter(adapter);

        Spinner stateSpin = (Spinner) findViewById(R.id.spinner2);
        // Create an ArrayAdapter using the string array and a default spinner
        // layout
        ArrayAdapter<CharSequence> adapterstate = ArrayAdapter
                .createFromResource(this, R.array.state,
                        android.R.layout.simple_spinner_item);
        // Specify the layout to use when the list of choices appears
        adapterstate
                .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        // Apply the adapter to the spinner
        stateSpin.setAdapter(adapterstate);

        Spinner citySpin = (Spinner) findViewById(R.id.spinner3);
        // Create an ArrayAdapter using the string array and a default spinner
        // layout
        ArrayAdapter<CharSequence> cityadapter = ArrayAdapter
                .createFromResource(this, R.array.City,
                        android.R.layout.simple_spinner_item);
        // Specify the layout to use when the list of choices appears
        cityadapter
                .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        // Apply the adapter to the spinner
        citySpin.setAdapter(cityadapter);

        subButton = (Button) findViewById(R.id.button1);
        subButton.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub

                String van = ""+vNumber.getText().toString();
                List<NameValuePair> nameValue = new ArrayList<NameValuePair>(1);
                nameValue.add(new BasicNameValuePair("VAN", van));
                try {
                    HttpClient httpClient = new DefaultHttpClient();
                    HttpPost httpPost = new HttpPost(
                            "http://10.0.2.2/tutorial.php");
                    httpPost.setEntity(new UrlEncodedFormEntity(nameValue));
                    HttpResponse httpResponse = httpClient.execute(httpPost);
                    HttpEntity entity = httpResponse.getEntity();
                    is=entity.getContent();
                    String msg = "Data Entered Succesfully";
                    Toast.makeText(getApplicationContext(), msg,
                            Toast.LENGTH_LONG).show();
                } catch (ClientProtocolException e) {
                    Log.e("ClientProtocol", "Log_Tag");
                    e.printStackTrace();
                } catch (IOException e) {
                    Log.e("Log_Tag", "IOException");
                    e.printStackTrace();
                }
                Intent intent = new Intent(UserOptions.this,
                        OnscreenActivity.class);
                intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
                startActivity(intent);

            }

        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.user_options, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

---

像这样更改代码

 @Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_user_options);
    ActionBar actionbar = getActionBar();
    actionbar.hide();
    vNumber = (EditText)findViewById(R.id.editText1);
    Spinner Schoolspin = (Spinner) findViewById(R.id.spinner1); 
    //Remaining code is as it is

}

setContentView（）

需要在调用

findviewbyid

之前。这就是编译器如何确定在哪里可以找到您的

edittext

更改此中的顺序：

 vNumber = (EditText)findViewById(R.id.editText1);

 setContentView(R.layout.activity_user_options);

你需要把：

    setContentView(R.layout.activity_user_options);
    vNumber = (EditText)findViewById(R.id.editText1);

onCreate（Bundle）

是初始化活动的地方。最重要的是，在这里，您通常会使用定义UI的布局资源调用

setContentView（view）

，并使用

findViewById（int）

检索该UI中需要以编程方式交互的小部件

但是“id”中的错误，如果小部件来自java类而没有设置为contentview，是否可以获取id

您必须创建动态视图，然后不需要调用setcontentview

setContentView(R.layout.activity_user_options);
vNumber = (EditText)findViewById(R.id.editText1);

---

你能编辑上面的代码并告诉我哪里错了吗？无法在数据库中输入数据，但这是一个新问题，不是吗？这是我的php文件对不起，它与你原来的问题没有任何关系。使用相关代码询问新问题

    setContentView(R.layout.activity_user_options);
    vNumber = (EditText)findViewById(R.id.editText1);

setContentView(R.layout.activity_user_options);
vNumber = (EditText)findViewById(R.id.editText1);