Question

我是android开发的新手。我正在使用android studio申请。我创建了DB，然后在Yii中创建了web service，在ARC上对其进行了测试并使用GET方法，它完美地显示了结果。之后我创建了一个app，其中我想使用web service并使用它的get方法来显示结果。

下面是我的数据库表结构

该方案是当用户在应用中输入id并点击提交按钮时，它应显示相应的username。为此，请参阅以下代码

清单

<uses-permission android:name="android.permission.INTERNET"/>

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">

        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

MainActivity.java

public class MainActivity extends AppCompatActivity {

String URLGET = "http://my_ip:8000/app/web/users/";
String result = "";
TextView tv;
public static final String LOG_TAG = MainActivity.class.getSimpleName();

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



    final Button button = (Button) findViewById(R.id.btn_Submit);


    button.setOnClickListener(new Button.OnClickListener() {


        @Override
        public void onClick(View v) {
            String reqURL = URLGET;

            new RestOperation().execute(reqURL);
            //callWebService(query);
        }
    });

}

public class RestOperation extends AsyncTask<String, Void, Void> {


    final HttpClient httpClient = new DefaultHttpClient();
    String content;
    String error;
    ProgressDialog progressDialog = new ProgressDialog(MainActivity.this);
    String data = "";

    TextView getData = (TextView) findViewById(R.id.getData);
    EditText userInput = (EditText) findViewById(R.id.EnterId);


    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        progressDialog.setTitle("Please Wait...");
        progressDialog.show();

        try {
            data += "&" + URLEncoder.encode("data", "UTF-8") + "-" + userInput.getText();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected Void doInBackground(String... params) {

        BufferedReader br = null;

        URL url = null;
        try {
            url = new URL(params[0]);


            URLConnection connection = url.openConnection();

            connection.setDoOutput(true);

            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(connection.getOutputStream());

            outputStreamWriter.write(data);
            outputStreamWriter.flush();

            br = new BufferedReader(new InputStreamReader(connection.getInputStream()));

            StringBuilder sb = new StringBuilder();

            String line = null;

            while ((line = br.readLine()) != null) {
                sb.append(line);
                sb.append(System.getProperty("line.separator"));


            }

            content = sb.toString();

        } catch (MalformedURLException e) {
            error = e.getMessage();
            e.printStackTrace();
        } catch (IOException e) {
            error = e.getMessage();
            e.printStackTrace();
        } finally {
            try {
                br.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);

        progressDialog.dismiss();

        if (error != null) {
            getData.setText("Error" + error);
        } else {
            getData.setText(content);


        }
    }
}

}

但是当我运行应用程序时，输入任何给定的ID并执行提交。进度棒显示了很长一段时间，然后应用程序崩溃，给出以下错误。

FATAL EXCEPTION: AsyncTask #1
                                                                           Process: com.example.accurat.webservice, PID: 642
                                                                           java.lang.RuntimeException: An error occured while executing doInBackground()
                                                                            at android.os.AsyncTask$3.done(AsyncTask.java:304)
                                                                            at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
                                                                            at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
                                                                            at java.util.concurrent.FutureTask.run(FutureTask.java:242)
                                                                            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
                                                                            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
                                                                            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
                                                                            at java.lang.Thread.run(Thread.java:818)
                                                                         Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedReader.close()' on a null object reference
                                                                            at com.example.accurat.webservice.MainActivity$RestOperation.doInBackground(MainActivity.java:141)
                                                                            at com.example.accurat.webservice.MainActivity$RestOperation.doInBackground(MainActivity.java:72)
                                                                            at android.os.AsyncTask$2.call(AsyncTask.java:292)
                                                                            at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                                                                            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
                                                                            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
                                                                            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
                                                                            at java.lang.Thread.run(Thread.java:818) 
02-07 15:57:42.929 642-642/com.example.accurat.webservice E/WindowManager: android.view.WindowLeaked: Activity com.example.accurat.webservice.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{3f2c8572 V.E..... R......D 0,0-729,322} that was originally added here
                                                                           at android.view.ViewRootImpl.<init>(ViewRootImpl.java:363)
                                                                           at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:271)
                                                                           at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)
                                                                           at android.app.Dialog.show(Dialog.java:298)
                                                                           at com.example.accurat.webservice.MainActivity$RestOperation.onPreExecute(MainActivity.java:90)
                                                                           at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:591)
                                                                           at android.os.AsyncTask.execute(AsyncTask.java:539)
                                                                           at com.example.accurat.webservice.MainActivity$1.onClick(MainActivity.java:65)
                                                                           at android.view.View.performClick(View.java:4780)
                                                                           at android.view.View$PerformClick.run(View.java:19866)
                                                                           at android.os.Handler.handleCallback(Handler.java:739)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                           at android.os.Looper.loop(Looper.java:135)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at java.lang.reflect.Method.invoke(Method.java:372)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

我搜索了谷歌上的很多文章，找不到正确的答案，虽然我试图实现它们但仍然没有结果。

以下是我搜索的结果。

link1
link2
link3
link 4

更新1

使用Ben和X3Btel建议我的应用停止崩溃，但它在模拟器上显示错误

然后我再次将ip替换为localhost，但仍然看到同样的错误。

我正在模拟器上测试我的应用，所以我将ip地址放在网址中。

我几乎整天都被困住了。任何帮助，将不胜感激。

Answer 1

您将获得nullpointer异常。

如果在初始化阅读器之前发生异常，则会导致此错误，因为br.close（）被放置在finally块中。在最终关闭资源之前，始终检查null 是一种很好的做法。

在finally块中尝试这个

if(br!= null)
br.close();

祝你好运

进度对话框继续在android studio中显示

1 个答案: