AlertDialog.Builder显示API请求

时间：2018-10-17 07:11:24

标签： java android android-alertdialog

我开始学习开发android应用程序（希望我能理解这项很棒的技术）。

我有一个REST API，可以使用PHP构建自己。

情况是，Android应用程序扫描QR码，然后将resultScan发送到我的Rest API。

这是我的代码：

import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.os.Build;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import com.google.zxing.Result;
import me.dm7.barcodescanner.zxing.ZXingScannerView;
import org.json.JSONObject;



public class InfoCoilActivity extends AppCompatActivity implements ZXingScannerView.ResultHandler {
    private static final int REQUEST_CAMERA = 1;
    private ZXingScannerView scannerView;
    private String responseResult;

    @Override
    public void handleResult(Result result) {
        final String scanResult = result.getText();
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Result Scan For Info Coil");
        builder.setPositiveButton("Continue", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                scannerView.resumeCameraPreview(InfoCoilActivity.this);
            }
        });
        builder.setMessage("Result " + handleRequestApi(scanResult));
        AlertDialog alert = builder.create();
        alert.show();
    }

    public String handleRequestApi(String textCode) {
        String URL = "http://my-web.com/api/morowali-coil/" + textCode;
        final RequestQueue requestQueue = Volley.newRequestQueue(this);

        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(
                Request.Method.GET,
                URL,
                null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        responseResult = response.toString();
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        responseResult = error.toString();
                    }
                }
        );
        requestQueue.add(jsonObjectRequest);
        return responseResult;
    }
}

请参阅builder.setMessage("Result " + handleRequestApi(scanResult)); 当我扫描第一张照片中的二维码时，收到消息

Result null

我尝试在logcat中看到，在第一张照片中，成功获得了这样的响应json：

10-17 14:07:01.492 11568-11568/com.dzil.myapplication E/Rest Response:: {"id":889,"coil_number":"QLZ18K01014A","planning_delivery":"WAREHOUSE","billet_number":"Y180908B03-4","width":0,"thickness":"0.00","grade":"S30403","size":"1.84*1250*C","actual_size":"1.85*1249","quantity":1,"nett":20930,"gross":21016,"customer":"IIS","contract_number":"IRNC18\/CC1137","procurement_contract_number":"","white_roll_number":"N1809100738","production_date":"2018-09-21","standard_eksekutif":"EN 10028-7","order_number":"ET18\/CC708001-IIS","unstuffing_plan":"2018-10-14","length":1143,"production_warehouse":"6#库","port":"Surabaya","vessel":null,"vessel_id":2,"urut":889,"lokasi":null,"lokasi_terakhir":null,"nama_file":"Copy of morowali-surabaya-example-format-data","created_by":"1","updated_by":"1","created_at":"2018-10-12 16:09:46","updated_at":"2018-10-12 16:09:46"}

但是当我再次尝试第二次尝试时，通常会得到上面的json之类的json 

Result {"id":889,"coil_number":"QLZ18K01014A","planning_delivery":"WAREHOUSE","billet_number":"Y180908B03-4","width":0,"thickness":"0.00","grade":"S30403","size":"1.84*1250*C","actual_size":"1.85*1249","quantity":1,"nett":20930,"gross":21016,"customer":"IIS","contract_number":"IRNC18\/CC1137","procurement_contract_number":"","white_roll_number":"N1809100738","production_date":"2018-09-21","standard_eksekutif":"EN 10028-7","order_number":"ET18\/CC708001-IIS","unstuffing_plan":"2018-10-14","length":1143,"production_warehouse":"6#库","port":"Surabaya","vessel":null,"vessel_id":2,"urut":889,"lokasi":null,"lokasi_terakhir":null,"nama_file":"Copy of morowali-surabaya-example-format-data","created_by":"1","updated_by":"1","created_at":"2018-10-12 16:09:46","updated_at":"2018-10-12 16:09:46"}

请咨询！

4 个答案:

答案 0 :(得分：2)

handleRequestApi是一种异步方法，这意味着它会在从您的API获取任何值之前返回。

因此return responseResult将始终返回null的初始值。

请参阅：Asynchronous vs synchronous execution, what does it really mean? 有关异步任务的更多信息

答案 1 :(得分：2)

由于异步，您不能这样做。因为handleRequestApi()方法没有请求的响应，所以第一个镜头返回null。第二张照片由于缓存而返回某些内容。

要正确使用异步，您必须直接在 onResponse()回调。您要显示AlertDialog吗？做这样的事情

@Override
public void onResponse(JSONObject response) {
    responseResult = response.toString();
    AlertDialog.Builder builder = new AlertDialog.Builder(InfoCoilActivity .this);
    builder.setTitle("Result Scan For Info Coil");
    builder.setPositiveButton("Continue", new DialogInterface.OnClickListener() 
    {
        @Override
        public void onClick(DialogInterface dialogInterface, int i) {
            scannerView.resumeCameraPreview(InfoCoilActivity.this);
        }
    });
    builder.setMessage("Result " + response);
    AlertDialog alert = builder.create();
    alert.show();
}

答案 2 :(得分：1)

您的对话框是立即创建的，无需等待响应，因为函数handleRequestApi(scanResult)是异步调用的，因此它显示为null，因为您活动中responseResult的初始值当时为null。 / p>

要解决此问题，只应在对话框收到响应时创建对话框：

new Response.Listener<JSONObject>() {
    @Override
    public void onResponse(JSONObject response) {
        AlertDialog dialog = new AlertDialog.Builder(this)
            .setTitle(...)
            .setPositiveButton(...)
            .setMessage(response.toString())
            .create();
        dialog.show();
    }
}, ...

答案 3 :(得分：0)

此错误是由于使用齐射和警报对话框的异步性引起的。您可以创建如下代码的自定义界面：

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute } from '@angular/router';

@Component({
  selector: 'app-hello',
  template: `<h2>Check Console for Output</h2>`,
})
export class HelloComponent implements OnInit {
  constructor(private route:ActivatedRoute){}
  ngOnInit(){
    this.route.queryParams.subscribe((query)=>{
      console.log(query);
      console.log("MODE",query['MODE']);//output MODE:p
    });
  }
}

并在您的代码中使用它。

public interface VolleyResponseListener{
    void onVolleyResponse(String response);        
}

注意：：我已添加和删除了一些代码。请注意public class InfoCoilActivity extends AppCompatActivity implements ZXingScannerView.ResultHandler, VolleyResponseListener { private static final int REQUEST_CAMERA = 1; private ZXingScannerView scannerView; private String responseResult; private VolleyResponseListener volleyResponseListener; public interface VolleyResponseListener{ void onVolleyResponse(String response); } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); volleyResponseListener = (VolleyResponseListener) this; //... your codes... } @Override public void handleResult(Result result) { handleRequestApi(result.getText()); } public void handleRequestApi(String textCode) { String URL = "http://my-web.com/api/morowali-coil/" + textCode; final RequestQueue requestQueue = Volley.newRequestQueue(this); JsonObjectRequest jsonObjectRequest = new JsonObjectRequest( Request.Method.GET, URL, null, new Response.Listener<JSONObject>() { @Override public void onResponse(JSONObject response) { volleyResponseListener.onVolleyResponse(response.toString()); } }, new Response.ErrorListener() { @Override public void onErrorResponse(VolleyError error) { volleyResponseListener.onVolleyResponse(error.toString()); } } ); requestQueue.add(jsonObjectRequest); } @Override public void onVolleyResponse(String response){ AlertDialog.Builder builder = new AlertDialog.Builder(this); builder.setTitle("Result Scan For Info Coil"); builder.setPositiveButton("Continue", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialogInterface, int i) { scannerView.resumeCameraPreview(InfoCoilActivity.this); } }); builder.setMessage("Result " + response); AlertDialog alert = builder.create(); alert.show(); } } 和implements。

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