Java 当JSON值为空时，应用程序崩溃

我有一个jsonArray，当数组为空时，我收到一个崩溃消息，说

应用程序不幸停止了

。但是如果数组为空，我想显示一个文本。我该怎么做？在过去的两天里，我陷入了这个问题JSON数组如下：

[{"head_name":null,"amount":null,"vat":null,"for_month":null,"status":null}]

以下是我的java代码：

String url_payment_jul = Config.PAYMENT_JUL_URL+"?reference="+Config.userInfo.get(5);
    JsonArrayRequest req_jul = new JsonArrayRequest(url_payment_jul,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response_jul) {
                    Log.d("my data", response_jul.toString());

                    try {
                        // Parsing json array response
                        // loop through each json object
                        String jsonResponse = "";
                        for (int i = 0; i < response_jul.length(); i++) {

                            JSONObject paymentInfo_jul = (JSONObject)response_jul.get(i);

                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("amount"));// Amount_jul in index (0)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("vat"));// VAT_jul in index (1)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("status"));// Status_jul in index (2)
                        }

                        String status_jul = Config.paymentInfo_jul.get(2);

                        if (status_jul == null){
                            textView_status_jul.setText(" Not Paid");

                        }else {
                            fixedAmount_jul();
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                        Toast.makeText(getApplicationContext(),
                                "Error: " + e.getMessage(),
                                Toast.LENGTH_LONG).show();
                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            VolleyLog.d(",y error", "Error: " + error.getMessage());
            Toast.makeText(getApplicationContext(),
                    error.getMessage(), Toast.LENGTH_SHORT).show();
        }
    });

String url\u payment\u jul=Config.payment\u jul\u url+”？reference=“+Config.userInfo.get（5）；
JsonArrayRequest req_jul=新JsonArrayRequest（url_payment_jul，
新的Response.Listener（）{
@凌驾
公共无效响应（JSONArray响应）{
Log.d（“我的数据”，response_jul.toString（））；
试一试{
//解析json数组响应
//循环遍历每个json对象
字符串jsonResponse=“”；
对于（int i=0；i

使用

或者，可以使用

optString

函数进一步简化

获取与键关联的可选字符串。它返回 如果没有这样的键，则默认值

 public String optString(String key, String defaultValue) {

试试这个：

Config.paymentInfo_jul.add(paymentInfo_jul.getString("amount") == null ? YOUR_DEFAULT_VALUE : paymentInfo_jul.getString("amount"));

请尝试以下代码段：

if(response_jul.toString().equals("Null")){
   Log.i("jsa","null");
}

---

对于这些问题，您必须使用try-and-catch-ladder代码让您的代码进入

try{
    String status_jul = Config.paymentInfo_jul.get(2);
fixedAmount_jul();                            
textView_status_jul.setText(" Not Paid");

   }catch {
   Toast.makeText(getApplicationContext(),"Error: " + e.getMessage(),Toast.LENGTH_LONG).show();
           }
}

在你的for循环中

try
{
 JSONObject paymentInfo_jul = (JSONObject) response_jul
                                    .get(i);

                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("amount"));// Amount_jul in index (0)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("vat"));// VAT_jul in index (1)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("status"));// Status_jul in index (2)
}
catch(Exception e)
{
       Toast.makeText(getApplicationContext(),"Error: " + e.getMessage(),Toast.LENGTH_LONG).show();

}

---

在每个使用if和else的地方，请使用try catch而不是if和else。

这样做解决了我的问题：

 if (status_jul.equals("null")){
                        textView_status_jul.setText(" Not Paid");

                    }else {
                        fixedAmount_jul();
                    }

---

首先在xml布局上创建一个文本视图，当jsonarray为空时显示文本，可见性为空

<TextView
        android:id="@+id/empty_view"
        android:padding="10dp"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="You have no new  notifications"
        android:visibility="gone" />

在onResponse（）方法上，在应用for循环之前，检查数组的长度，如果长度为0，则使textview的可见性与

if(response_jul.length()==0){
emptyView.setVisibility(View.VISIBLE);
}else{
 for (int i = 0; i < response_jul.length(); i++) {

                            JSONObject paymentInfo_jul = (JSONObject) response_jul
                                    .get(i);

                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("amount"));// Amount_jul in index (0)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("vat"));// VAT_jul in index (1)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("status"));// Status_jul in index (2)
                        }


                        String status_jul = Config.paymentInfo_jul.get(2);

                        if (status_jul == null){
                            textView_status_jul.setText(" Not Paid");

                        }else {
                            fixedAmount_jul();
                        }

}

if（响应长度（）==0）{
emptyView.setVisibility（View.VISIBLE）；
}否则{
对于（int i=0；i

当数组为空时显示Json

 if (status_jul.equals("null")){
                        textView_status_jul.setText(" Not Paid");

                    }else {
                        fixedAmount_jul();
                    }

<TextView
        android:id="@+id/empty_view"
        android:padding="10dp"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="You have no new  notifications"
        android:visibility="gone" />

if(response_jul.length()==0){
emptyView.setVisibility(View.VISIBLE);
}else{
 for (int i = 0; i < response_jul.length(); i++) {

                            JSONObject paymentInfo_jul = (JSONObject) response_jul
                                    .get(i);

                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("amount"));// Amount_jul in index (0)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("vat"));// VAT_jul in index (1)
                            Config.paymentInfo_jul.add( paymentInfo_jul.getString("status"));// Status_jul in index (2)
                        }


                        String status_jul = Config.paymentInfo_jul.get(2);

                        if (status_jul == null){
                            textView_status_jul.setText(" Not Paid");

                        }else {
                            fixedAmount_jul();
                        }

}