Android App Closes Unexpectedly

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I followed the steps and just copied the programming from the google website. I made a button, that it checks the connection with my network, through the IP and Port, when clicking the button, if it has connection with the network, it shows a Toast with error message, and if there is connection it edits the text field of the screen of the app. I followed the steps of this link: http://developer.android.com/intl/pt-br/training/basics/network-ops/connecting.html My problem, is that by clicking the button, the application closes and the android returns the message "Unfortunately the app stopped".

Below is the source code.

Mainactivity.java

 package start.home.app;

import java.io.IOException;
import android.app.Activity;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;


public class MainActivity extends Activity {

Button btnSolicitar;
EditText editResultado;

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

    btnSolicitar=(Button)findViewById(R.id.btnSolicitar);
    btnSolicitar.setOnClickListener(new View.OnClickListener() {            
        @Override
        public void onClick(View v) {

            String stringUrl = "192.168.0.1:8080/teste.html";


            ConnectivityManager connMgr = (ConnectivityManager) 
                    getSystemService(Context.CONNECTIVITY_SERVICE);


            NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
            if (networkInfo != null && networkInfo.isConnected()) {
                new DownloadWebpageTask().execute(stringUrl);
            } else {
                Toast.makeText(getApplicationContext(), "Nenhuma Conexão Encontrada!", Toast.LENGTH_LONG).show();
            }
        }
    });

}

private class DownloadWebpageTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {
        try {               
            Conexao conexao = new Conexao();

            return conexao.downloadUrl(urls[0]);
        } catch (IOException e) {
            return "Servidor Não Encontrado!";
        }
    }
    // onPostExecute displays the results of the AsyncTask.
    @Override
    protected void onPostExecute(String resultado) {
        // textView.setText(result);
        editResultado.setText(resultado);
    }
}

@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 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);
    }
}

Java connection.

package start.home.app;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;

public class Conexao {

// Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string.
public String downloadUrl(String myurl) throws IOException {
    InputStream is = null;
    // Only display the first 500 characters of the retrieved
    // web page content.
    int len = 500;

    try {
        URL url = new URL(myurl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setReadTimeout(10000 /* milliseconds */);
        conn.setConnectTimeout(15000 /* milliseconds */);
        conn.setRequestMethod("GET");
        conn.setDoInput(true);
        // Starts the query
        conn.connect();
        is = conn.getInputStream();

        // Convert the InputStream into a string
        String contentAsString = readIt(is, len);
        return contentAsString;

    // Makes sure that the InputStream is closed after the app is
    // finished using it.
    } finally {
        if (is != null) {
            is.close();
        } 
    }
}

// Reads an InputStream and converts it to a String.
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
    Reader reader = null;
    reader = new InputStreamReader(stream, "UTF-8");        
    char[] buffer = new char[len];
    reader.read(buffer);
    return new String(buffer);
 }

}

I added permissions to Androidmanifest

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

When emulating normally, logcat looks like this.

12-29 22:50:01.357: D/HyLog(32639): I : /data/font/config/sfconfig.dat, No such file or directory (2)
12-29 22:50:01.357: D/HyLog(32639): I : /data/font/config/dfactpre.dat, No such file or directory (2)
12-29 22:50:01.357: D/HyLog(32639): I : /data/font/config/sfconfig.dat, No such file or directory (2)
12-29 22:50:01.547: D/BubblePopupHelper(32639): isShowingBubblePopup : false
12-29 22:50:01.627: I/Adreno-EGL(32639): <qeglDrvAPI_eglInitialize:410>: EGL 1.4 QUALCOMM build: AU_LINUX_ANDROID_KK_3.5_RB1.04.04.02.006.089_msm8610_KK_3.5_RB1__release_AU ()
12-29 22:50:01.627: I/Adreno-EGL(32639): OpenGL ES Shader Compiler Version: E031.24.00.06
12-29 22:50:01.627: I/Adreno-EGL(32639): Build Date: 01/30/14 Thu
12-29 22:50:01.627: I/Adreno-EGL(32639): Local Branch: 
12-29 22:50:01.627: I/Adreno-EGL(32639): Remote Branch: quic/kk_3.5_rb1.21
12-29 22:50:01.627: I/Adreno-EGL(32639): Local Patches: NONE
12-29 22:50:01.627: I/Adreno-EGL(32639): Reconstruct Branch: AU_LINUX_ANDROID_KK_3.5_RB1.04.04.02.006.089 +  NOTHING
12-29 22:50:01.727: D/OpenGLRenderer(32639): Enabling debug mode 0
12-29 22:50:01.757: D/BubblePopupHelper(32639): isShowingBubblePopup : false
12-29 22:50:01.757: D/BubblePopupHelper(32639): isShowingBubblePopup : false
12-29 22:50:01.787: D/BubblePopupHelper(32639): isShowingBubblePopup : false
12-29 22:50:01.787: D/BubblePopupHelper(32639): isShowingBubblePopup : false
12-29 22:50:01.837: I/ActivityManager(32639): Timeline: Activity_idle id: android.os.BinderProxy@4246c860 time:17786129

After I click the button, these messages appear in the logcat.

12-29 22:50:16.187: I/ViewRootImpl(32639): ViewRoot's Touch Event : ACTION_DOWN
12-29 22:50:16.197: I/ViewRootImpl(32639): ViewRoot's Touch Event : ACTION_UP
12-29 22:50:16.257: D/AndroidRuntime(32639): Shutting down VM
12-29 22:50:16.257: W/dalvikvm(32639): threadid=1: thread exiting with uncaught exception (group=0x41e85e90)
12-29 22:50:16.267: E/AndroidRuntime(32639): FATAL EXCEPTION: main
12-29 22:50:16.267: E/AndroidRuntime(32639): Process: start.home.app, PID: 32639
12-29 22:50:16.267: E/AndroidRuntime(32639): java.lang.NullPointerException
12-29 22:50:16.267: E/AndroidRuntime(32639):    at start.home.app.MainActivity$DownloadWebpageTask.onPostExecute(MainActivity.java:66)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at start.home.app.MainActivity$DownloadWebpageTask.onPostExecute(MainActivity.java:1)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at android.os.AsyncTask.finish(AsyncTask.java:632)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at android.os.AsyncTask.access$600(AsyncTask.java:177)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at android.os.Handler.dispatchMessage(Handler.java:102)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at android.os.Looper.loop(Looper.java:136)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at android.app.ActivityThread.main(ActivityThread.java:5118)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at java.lang.reflect.Method.invokeNative(Native Method)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at java.lang.reflect.Method.invoke(Method.java:515)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606)
12-29 22:50:16.267: E/AndroidRuntime(32639):    at dalvik.system.NativeStart.main(Native Method)

If necessary, I can download the project. Or even the app apk file.

1 answer

0


You’re getting an NPE, you’re trying to access a property of a component that is NULL. This is a exception frequent.

In your case, you did not set the object to the element.

At your event OnCreate do so:

// veja o nome que você deu pro seu TextView
editResultado = (TextView) findViewById(R.id.textView1);

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