向数据库添加新行并意外关闭应用程序答案

【问题标题】：Adding new line to database and unexpectedly closes app向数据库添加新行并意外关闭应用程序
【发布时间】：2015-12-12 20:55:43
【问题描述】：

我目前是 android 编程的初学者，现在我正在开发一个应用程序来与 LAMP 服务器建立 JSON 连接并显示 JSON 数据。目前已成功建立连接，我可以创建产品并在数据库中查看它，但应用程序每次都意外关闭，有人可以帮助我并指出正确的方向，如果需要会添加更多内容。

public class JSONParser {

static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

// constructor
public JSONParser() {

}

// function get json from url
// by making HTTP POST or GET mehtod
public JSONObject makeHttpRequest(String url, String method,
                                  List<NameValuePair> params) {

    is = null;
    jObj = null;
    json = "";

    // Making HTTP request
    try {

        Log.i("url", url);

        // check for request method
        if(method == "POST"){
            // request method is POST
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            Log.i("url", url);
            HttpPost httpPost = new HttpPost(url);

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();

        }else if(method == "GET"){
            // request method is GET
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            Log.i("url", url);
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }


    Log.i("Stage 1", "Stage 1");

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);

        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");

            Log.i("1 ", line);
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    Log.i("Stage 2", "Stage 2");

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    Log.i("Stage 3", "Stage 3");

    // return JSON String
    return jObj;

}

public class NewProductActivity extends Activity {


// Progress Dialog
private ProgressDialog pDialog;

JSONParser jsonParser = new JSONParser();
EditText inputName;
EditText inputPrice;
EditText inputDesc;

// url to create new product
private static String url_create_product = "http://192.168.1.165/wp-admin/android_connect/create_product.php";

// JSON Node names
private static final String TAG_SUCCESS = "success";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.add_product);

    // Edit Text
    inputName = (EditText) findViewById(R.id.inputName);
    inputPrice = (EditText) findViewById(R.id.inputPrice);
    inputDesc = (EditText) findViewById(R.id.inputDesc);

    // Create button
    Button btnCreateProduct = (Button) findViewById(R.id.btnCreateProduct);

    // button click event
    btnCreateProduct.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {
            // creating new product in background thread
            new CreateNewProduct().execute();
        }
    });
}

/**
 * Background Async Task to Create new product
 * */
class CreateNewProduct extends AsyncTask<String, String, String> {

    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(NewProductActivity.this);
        pDialog.setMessage("Creating Product..");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    /**
     * Creating product
     * */
    @SuppressWarnings("ResourceType")
    protected String doInBackground(String... args) {
        String name = inputName.getText().toString();
        String price = inputPrice.getText().toString();
        String description = inputDesc.getText().toString();

        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("name", name));
        params.add(new BasicNameValuePair("price", price));
        params.add(new BasicNameValuePair("description", description));

        // getting JSON Object
        // Note that create product url accepts POST method
        JSONObject json = jsonParser.makeHttpRequest(url_create_product,
                "POST", params);

        // check log cat fro response
        Log.d("Create Response", json.toString());

        // check for success tag
        try {
            int success = json.getInt(TAG_SUCCESS);

            if (success == 1) {
                // successfully created product
                Intent i = new Intent(getApplicationContext(), AllProductsActivity.class);
                startActivity(i);

                // closing this screen
                finish();
            } else {
                // failed to create product
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;
    }

    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
        // dismiss the dialog once done
        pDialog.dismiss();
    }

}

logcat 09-16 10:47:27.285 23440-23458/com.example.androidhive.productjsonphp I/OpenGLRenderer：初始化 EGL，版本 1.4 09-16 10:47:27.287 23440-23458/com.example.androidhive.productjsonphp D/OpenGLRenderer：启用调试模式 0 09-16 10:47:28.372 23440-23440/com.example.androidhive.productjsonphp V/Monotype： SetAppTypeFace- 尝试翻转，app = com.example.androidhive.productjsonphp 09-16 10:47:28.372 23440-23440/com.example.androidhive.productjsonphp V/Monotype：字体 getFontPathFlipFont - systemFont = default#default 09-16 10:47:28.449 23440-23471/com.example.androidhive.productjsonphp 我/网址﹕ http://api.androidhive.info/android_connect/get_all_products.php 09-16 10:47:28.451 23440-23471/com.example.androidhive.productjsonphp 我/网址﹕ http://api.androidhive.info/android_connect/get_all_products.php? 09-16 10:47:28.674 23440-23458/com.example.androidhive.productjsonphp D/OpenGLRenderer：endAllStagingAnimators on 0xb7f62f50 (RippleDrawable) 与句柄 0xb7f75e00 09-16 10:47:29.017 23440-23471/com.example.androidhive.productjsonphp I/Stage 1: Stage 1 09-16 10:47:29.022 23440-23471/com.example.androidhive.productjsonphp I / 1：未知数据库'download_androidhive'09-16 10：47：29.022 23440-23471/com.example.androidhive.productjsonphp I/第 2 阶段：第 2 阶段 09-16 10:47:29.023 23440-23471/com.example.androidhive.productjsonphp E/JSON Parser﹕解析数据时出错 org.json.JSONException: Value 未知类型的 java.lang.String 无法转换为 JSONObject 09-16 10:47:29.023 23440-23471/com.example.androidhive.productjsonphp I/Stage 3: Stage 3 09-16 10:47:29.029 23440-23471/com.example.androidhive.productjsonphp E/AndroidRuntime﹕ 致命异常：AsyncTask #1 进程：com.example.androidhive.productjsonphp，PID：23440 java.lang.RuntimeException：执行 doInBackground() 时发生错误在 android.os.AsyncTask$3.done(AsyncTask.java:300) 在 java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355) 在 java.util.concurrent.FutureTask.setException(FutureTask.java:222) 在 java.util.concurrent.FutureTask.run(FutureTask.java:242) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 在 java.lang.Thread.run(Thread.java:818) 引起：java.lang.NullPointerException：尝试调用虚拟方法'java.lang.String org.json.JSONObject.toString()' 空对象引用在 com.example.androidhive.productjsonphp.AllProductsActivity$LoadAllProducts.doInBackground(AllProductsActivity.java:130) 在 com.example.androidhive.productjsonphp.AllProductsActivity$LoadAllProducts.doInBackground(AllProductsActivity.java:105) 在 android.os.AsyncTask$2.call(AsyncTask.java:288) 在 java.util.concurrent.FutureTask.run(FutureTask.java:237) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 在 java.lang.Thread.run(Thread.java:818) 09-16 10:47:29.528 23440-23440/com.example.androidhive.productjsonphp E/WindowManager﹕android.view.WindowLeaked: Activity com.example.androidhive.productjsonphp.AllProductsActivity 已泄露窗口 com.android.internal.policy.impl.PhoneWindow$DecorView{78d7c4f V.E..... R......D 0,0-479,116} 最初添加在这里在 android.view.ViewRootImpl.(ViewRootImpl.java:363) 在 android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:261) 在 android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69) 在 android.app.Dialog.show(Dialog.java:298) 在 com.example.androidhive.productjsonphp.AllProductsActivity$LoadAllProducts.onPreExecute(AllProductsActivity.java:117) 在 android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587) 在 android.os.AsyncTask.execute(AsyncTask.java:535) 在 com.example.androidhive.productjsonphp.AllProductsActivity.onCreate(AllProductsActivity.java:57) 在 android.app.Activity.performCreate(Activity.java:5975) 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2378) 在 android.app.ActivityThread.access$800(ActivityThread.java:147) 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1281) 在 android.os.Handler.dispatchMessage(Handler.java:102) 在 android.os.Looper.loop(Looper.java:135) 在 android.app.ActivityThread.main(ActivityThread.java:5255) 在 java.lang.reflect.Method.invoke（本机方法）在 java.lang.reflect.Method.invoke(Method.java:372) 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:838) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:651) 09-16 10:47:34.521 23440-23471/com.example.androidhive.productjsonphp I/Process﹕发送信号。 PID：23440 SIG：9

【问题讨论】：

标签： javascript android json android-asynctask lampp

【解决方案1】：

您尝试从字符串“json”解析Json，但是这个“json”字符串给出空值，如果请检查“json”字符串是否为空，然后再使用它。

那么，试试这段代码

if(json!=null && !json.equals(""))
{
try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
)else{
Toast.makeText(context, "json is empty", Toast.LENGTH_LONG).show();
}

【讨论】：