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AlertDialog.Builder从API请求中显示空值

android-alertdialog android java
  •  0
  • Fadly Dzil  · 技术社区  · 7 年前

    我有一个restapi,我自己用PHP构建。

    这是我的密码: 

    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;
    }
}

    请进来看看 builder.setMessage("Result " + handleRequestApi(scanResult)); 当我第一次扫描二维码时,我收到了一条信息 

    Result null

    我试着在logcat中看到,在第一个镜头中,成功地得到如下json响应: 

    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"}

    但当我在第二个镜头中再次尝试时,我得到上面那些类似json的json是很正常的 

    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"}

    请指教!

    4 回复  |  直到 7 年前
        1
  •  2
  •   marmor    7 年前

    handleRequestApi 是一个异步方法,意味着它返回 之前 从API中获取任何值。

    所以 return responseResult 将始终返回null的初始值。

    请参见: Asynchronous vs synchronous execution, what does it really mean?

        2
  •  2
  •   Bruno    7 年前

    你不能这样做,因为异步。第一个快照返回null,因为 handleRequestApi() 方法没有请求的响应。第二个镜头返回的东西,因为缓存。

    要正确使用异步,必须直接在 onResponse() 回拨。要显示警报对话框吗?做这样的事 

    @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();
}
        3
  •  1
  •   Aaron    7 年前

    由于函数 handleRequestApi(scanResult) 异步调用,因此它显示为null,因为 responseResult 在您的活动中,当时为空。

    要解决此问题,应仅在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();
    }
}, ...
        4
  •  0
  •   Sina Khorshidian    7 年前

    此错误是由于使用截击和警报对话框时的异步性造成的。您可以创建如下代码所示的自定义界面: 

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



    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();
    }

}

    注意: implements 和 onCreate .

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