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我正在尝试创建简单的登录表单。如果验证了用户凭据，则以下 URL 返回“true”，否则返回“false”。返回简单字符串。

http://......../login.php?user=rashid&pass=rashid

当我按下登录按钮时程序崩溃。这在 LogCat 上显示：-

致命异常：main - com.example.logintry.MainActivity$VerifyLogin.onPostExecution 处的 java.lang.NullPointerException

这是activit_main.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"    
android:padding="10dp"
 >

<EditText
    android:id="@+id/etUser"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="User Name"
    android:text="rashid"
    android:ems="10" >

    <requestFocus />
</EditText>

<EditText
    android:id="@+id/etPassword"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:hint="Password"
    android:text="rashid123"
    android:inputType="textPassword" />

<Button
    android:id="@+id/bLogin"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Login" />

</LinearLayout>

这是 MainActivity.java 出于安全原因，我没有添加实际 IP。

package com.example.logintry;

import java.io.IOException;
import java.net.URL;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity implements View.OnClickListener {

private EditText etUser, etPassword;
private Button bLogin;
private String u, p;
private final String KEY_LOGIN_URL = "http://.............../login.php";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    etUser = (EditText) findViewById(R.id.etUser);
    etPassword = (EditText) findViewById(R.id.etPassword);
    bLogin = (Button) findViewById(R.id.bLogin);
    bLogin.setOnClickListener(this);
}

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

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    u = etUser.getText().toString();
    p = etPassword.getText().toString();
    VerifyLogin runner = new VerifyLogin();
    runner.execute();

}

private class VerifyLogin extends AsyncTask<URL, Void, Void> {
    String msg = "";
    HttpClient httpClient;
    HttpGet httpGet;
    HttpResponse response;
    HttpEntity entity;

    @Override
    protected Void doInBackground(URL... urls) {
        // TODO Auto-generated method stub
        try {
            httpClient = new DefaultHttpClient();
            httpGet = new HttpGet(KEY_LOGIN_URL + "?user=" + u + "&pass=" + p);
            response = httpClient.execute(httpGet);
            entity = response.getEntity();
            msg = EntityUtils.toString(entity);

        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);

        if (result.equals("true")) {
            Toast.makeText(getApplicationContext(), "Valid password",
                    Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(getApplicationContext(), "Invalid Password",
                    Toast.LENGTH_LONG).show();
        }

    }

}

}
4

1 回答 1

1

result 是 type Void，它始终为 null，因此result.equals("true")会抛出 NPE。

您需要将您的 VerifyLogin 类更改为extends AsyncTask<URL, Void, String>，并使 doInBackground 返回“true”或“false”，就像您的 postExecution 方法所期望的那样。

于 2013-11-12T03:41:51.937 回答