有没有办法消除这个空对象引用错误？我正在尝试从扫描仪活动中打开一个底部对话框答案

【问题标题】：Is there any way to remove this nullobject reference error? I am trying to open a bottom dialog from scanner activity有没有办法消除这个空对象引用错误？我正在尝试从扫描仪活动中打开一个底部对话框
【发布时间】：2021-07-20 12:51:48
【问题描述】：

错误：

 E/AndroidRuntime: FATAL EXCEPTION: main
     Process: com.example.swiftpass, PID: 16875
     java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
         at com.example.swiftpass.ScanPopUpDialog.setPrompt(ScanPopUpDialog.java:47)
         at com.example.swiftpass.ScanQrActivity$MyImageAnalyzer.readerBarcodeData(ScanQrActivity.java:170)
         at com.example.swiftpass.ScanQrActivity$MyImageAnalyzer.access$200(ScanQrActivity.java:109)
         at com.example.swiftpass.ScanQrActivity$MyImageAnalyzer$3.onSuccess(ScanQrActivity.java:142)
         at com.example.swiftpass.ScanQrActivity$MyImageAnalyzer$3.onSuccess(ScanQrActivity.java:138)
         at com.google.android.gms.tasks.zzn.run(com.google.android.gms:play-services-tasks@@17.2.0:4)
         at android.os.Handler.handleCallback(Handler.java:789)
         at android.os.Handler.dispatchMessage(Handler.java:98)
         at android.os.Looper.loop(Looper.java:164)
         at android.app.ActivityThread.main(ActivityThread.java:6944)
         at java.lang.reflect.Method.invoke(Native Method)
         at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

XML 代码：

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout
     xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical">

     <RelativeLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content">

         <ImageView
             android:id="@+id/img_close"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginStart="10dp"
             android:layout_marginTop="10dp"
             android:src="@drawable/ic_close">
         </ImageView>

         <TextView
             android:id="@+id/txt_type"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_centerHorizontal="true"
             android:layout_marginTop="6dp"
             android:text="@string/qr_type"
             android:fontFamily="@font/roboto_black"
             android:textSize="20dp">
         </TextView>

         <TextView
             android:id="@+id/txt_prompt"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_centerHorizontal="true"
             android:layout_marginTop="50dp"
             android:layout_marginBottom="10dp"
             android:text="@string/qr_prompt"
             android:fontFamily="@font/roboto_medium"
             android:textSize="18dp">
         </TextView>

     </RelativeLayout>

 </LinearLayout>

底部对话框 java:

包 com.example.swiftpass;

导入android.os.Bundle；导入 android.view.LayoutInflater；导入android.view.View；导入android.view.ViewGroup；导入android.widget.ImageView；导入 android.widget.TextView；导入androidx.annotation.NonNull；导入androidx.annotation.Nullable;

导入 com.google.android.material.bottomsheet.BottomSheetDialogFragment；

公共类 ScanPopUpDialog 扩展 BottomSheetDialogFragment {

 //Declaration of Variables

 TextView type;
 TextView prompt;
 ImageView close;

 @Nullable
 @Override
 public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
     View view = inflater.inflate(R.layout.pop_up_dialog, container, false);

     type = view.findViewById(R.id.txt_type);
     prompt = view.findViewById(R.id.txt_prompt);
     close = view.findViewById(R.id.img_close);
     close.setOnClickListener(this::OnClick);
     return view;
 }

 //This function will listen to button clicks and will call certain functions according to what is pressed by the user
 private void OnClick(View view) {
     switch(view.getId()){
         case R.id.img_close:
             dismiss();
             break;
         case R.id.txt_prompt:
             break;
     }
 }

 public void setPrompt(String type, String prompt){
     this.type.setText(type);
     this.prompt.setText(prompt);

     if (type == "TEXT"){
         this.prompt.setOnClickListener(this::OnClick);
     }
 }

}

扫描仪活动java：

包 com.example.swiftpass;

导入 androidx.annotation.NonNull; 导入androidx.appcompat.app.AppCompatActivity；导入androidx.camera.core.CameraSelector；导入androidx.camera.core.ImageAnalysis；导入androidx.camera.core.ImageCapture；导入androidx.camera.core.ImageProxy；导入androidx.camera.core.Preview；导入androidx.camera.lifecycle.ProcessCameraProvider；导入androidx.camera.view.PreviewView；导入androidx.core.app.ActivityCompat；导入androidx.core.content.ContextCompat；导入androidx.fragment.app.FragmentManager；

导入 android.Manifest; 导入 android.annotation.SuppressLint；导入 android.content.pm.PackageManager；导入android.graphics.Point；导入android.graphics.Rect；导入android.media.Image；导入android.os.Bundle；导入android.util.Size；导入android.widget.Toast；

导入 com.google.android.gms.tasks.OnCompleteListener; 导入 com.google.android.gms.tasks.OnFailureListener；导入 com.google.android.gms.tasks.OnSuccessListener；导入 com.google.android.gms.tasks.Task；导入 com.google.common.util.concurrent.ListenableFuture；导入 com.google.mlkit.vision.barcode.Barcode；导入 com.google.mlkit.vision.barcode.BarcodeScanner；导入 com.google.mlkit.vision.barcode.BarcodeScannerOptions；导入 com.google.mlkit.vision.barcode.BarcodeScanning；导入 com.google.mlkit.vision.common.InputImage；

导入 java.util.List; 导入 java.util.concurrent.ExecutionException；导入 java.util.concurrent.ExecutorService；导入 java.util.concurrent.Executors;

公共类 ScanQrActivity 扩展 AppCompatActivity {

 //Declaration of Variables

 private ListenableFuture cameraProviderFuture;
 private ExecutorService cameraExecutor;
 private PreviewView previewView;
 private MyImageAnalyzer analyzer;

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

     //Assigning of widgets and Setting up of listeners
     initializeScan();


     cameraProviderFuture.addListener(new Runnable() {
         @Override
         public void run() {
             try {
                 if (ActivityCompat.checkSelfPermission(ScanQrActivity.this, Manifest.permission.CAMERA) != (PackageManager.PERMISSION_GRANTED)){
                     ActivityCompat.requestPermissions(ScanQrActivity.this, new String [] {Manifest.permission.CAMERA}, 101);
                 }else{
                     ProcessCameraProvider processCameraProvider = (ProcessCameraProvider) cameraProviderFuture.get();
                     bindPreview(processCameraProvider);
                 }
             }catch (ExecutionException e){
                 e.printStackTrace();
             }catch (InterruptedException e){
                 e.printStackTrace();
             }
         }
     }, ContextCompat.getMainExecutor(this));
 }

 @Override
 public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
     if (requestCode == 101 && grantResults.length > 0){
         ProcessCameraProvider processCameraProvider = null;
         try {
             processCameraProvider = (ProcessCameraProvider) cameraProviderFuture.get();
         } catch (ExecutionException e) {
             e.printStackTrace();
         } catch (InterruptedException e) {
             e.printStackTrace();
         }
         bindPreview(processCameraProvider);
     }
 }

 private void bindPreview(ProcessCameraProvider processCameraProvider) {

     Preview preview = new Preview.Builder().build();
     CameraSelector cameraSelector = new CameraSelector.Builder().requireLensFacing(CameraSelector.LENS_FACING_BACK).build();
     preview.setSurfaceProvider(previewView.getSurfaceProvider());
     ImageCapture imageCapture = new ImageCapture.Builder().build();
     ImageAnalysis imageAnalysis = new ImageAnalysis.Builder()
             .setTargetResolution(new Size(1280, 720))
             .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
             .build();
     imageAnalysis.setAnalyzer(cameraExecutor, analyzer);
     processCameraProvider.unbindAll();
     processCameraProvider.bindToLifecycle(this,cameraSelector, preview, imageCapture, imageAnalysis);
 }

 public class MyImageAnalyzer implements ImageAnalysis.Analyzer{
     private FragmentManager fragmentManager;
     private ScanPopUpDialog bottomDialog;

     public MyImageAnalyzer(FragmentManager fragmentManager){
         this.fragmentManager = fragmentManager;
         bottomDialog = new ScanPopUpDialog();
     }

     @Override
     public void analyze(@NonNull ImageProxy imageProxy) {
          scanBarcode(imageProxy);
     }

     private void scanBarcode(ImageProxy imageProxy) {

         BarcodeScannerOptions options =
                 new BarcodeScannerOptions.Builder()
                         .setBarcodeFormats(
                                 Barcode.FORMAT_QR_CODE)
                         .build();

         @SuppressLint("UnsafeExperimentalUsageError") Image mediaImage = imageProxy.getImage();
         assert mediaImage != null;
         InputImage inputImage =
                 InputImage.fromMediaImage(mediaImage, imageProxy.getImageInfo().getRotationDegrees());

         BarcodeScanner scanner = BarcodeScanning.getClient(options);
         Task<List<Barcode>> result = scanner.process(inputImage)
                 .addOnSuccessListener(new OnSuccessListener<List<Barcode>>() {
                     @Override
                     public void onSuccess(List<Barcode> barcodes) {
                         // Task completed successfully
                         readerBarcodeData(barcodes);
                     }
                 })
                 .addOnFailureListener(new OnFailureListener() {
                     @Override
                     public void onFailure(@NonNull Exception e) {
                         // Task failed with an exception
                         // ...
                         e.printStackTrace();
                     }
                 })
                 .addOnCompleteListener(new OnCompleteListener<List<Barcode>>() {
                     @Override
                     public void onComplete(@NonNull Task<List<Barcode>> task) {
                         imageProxy.close();
                     }
                 });
     }

     private void readerBarcodeData(List<Barcode> barcodes) {
         for (Barcode barcode: barcodes) {
             Rect bounds = barcode.getBoundingBox();
             Point[] corners = barcode.getCornerPoints();

             String rawValue = barcode.getRawValue();
             int valueType = barcode.getValueType();
             switch (valueType){
                 case Barcode.TYPE_TEXT:
                     bottomDialog.setPrompt(rawValue, "CLICK TO CONFIRM");
                     break;
                 case Barcode.TYPE_CALENDAR_EVENT:
                     bottomDialog.setPrompt("Calendar Event", "Unsupported Type");
                     break;
                 case Barcode.TYPE_CONTACT_INFO:
                     bottomDialog.setPrompt("Contact Info", "Unsupported Type");
                     break;
                 case Barcode.TYPE_DRIVER_LICENSE:
                     bottomDialog.setPrompt("Driver's License", "Unsupported Type");
                     break;
                 case Barcode.TYPE_EMAIL:
                     bottomDialog.setPrompt("E-mail", "Unsupported Type");
                     break;
                 case Barcode.TYPE_GEO:
                     bottomDialog.setPrompt("Location", "Unsupported Type");
                     break;
                 case Barcode.TYPE_ISBN:
                     bottomDialog.setPrompt("Book Number", "Unsupported Type");
                     break;
                 case Barcode.TYPE_PHONE:
                     bottomDialog.setPrompt("Phone", "Unsupported Type");
                     break;
                 case Barcode.TYPE_PRODUCT:
                     bottomDialog.setPrompt("Product", "Unsupported Type");
                     break;
                 case Barcode.TYPE_SMS:
                     bottomDialog.setPrompt("SMS", "Unsupported Type");
                     break;
                 case Barcode.TYPE_URL:
                     bottomDialog.setPrompt("Link", "Unsupported Type");
                     break;
                 case Barcode.TYPE_WIFI:
                     bottomDialog.setPrompt("Wi-Fi", "Unsupported Type");
                     break;
                 default:
                     bottomDialog.setPrompt("Uknown", "Uknown Type");
             }
             if (!bottomDialog.isAdded()){
                 bottomDialog.show(fragmentManager, "");
             }
         }
     }
 }


 private void initializeScan() {
     previewView = findViewById(R.id.previewView);
     this.getWindow().setFlags(1024,1024);
     cameraExecutor = Executors.newSingleThreadExecutor();
     cameraProviderFuture = ProcessCameraProvider.getInstance(this);
     analyzer = new MyImageAnalyzer(getSupportFragmentManager());
 }

}

【问题讨论】：

标签： android

【解决方案1】：

我解决了，代码如下：

package com.example.swiftpass;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.google.android.material.bottomsheet.BottomSheetDialogFragment;


public class ScanPopUpDialog extends BottomSheetDialogFragment {

    //Declaration of Variables

    TextView type;
    TextView prompt;
    ImageView close;
    String stringType;
    String stringPrompt;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.pop_up_dialog, container, false);

        type = view.findViewById(R.id.txt_type);
        type.setText(getStringType());
        prompt = view.findViewById(R.id.txt_prompt);
        prompt.setText(getStringPrompt());
        if (stringPrompt == "CLICK TO CONFIRM"){
            prompt.setOnClickListener(this::OnClick);
        }
        close = view.findViewById(R.id.img_close);
        close.setOnClickListener(this::OnClick);
        return view;
    }

    //This function will listen to button clicks and will call certain functions according to what is pressed by the user
    private void OnClick(View view) {
        switch(view.getId()){
            case R.id.img_close:
                dismiss();
                break;
            case R.id.txt_prompt:
                break;
        }
    }

    public void setDialog(String type, String prompt){
        /**
         * This method is public because it is being called fron the scan qr activity
         * this will set the value for the objects stringType and stringPrompt
         * this does not return any value thus, the values will be accessed through
         * get method
         */
        stringType = type;
        stringPrompt = prompt;
    }

    /**
     *These methods are used to access the value set by the setDialog method
     *
     */
    private String getStringType(){
        return stringType;
    }

    private String getStringPrompt(){
        return stringPrompt;
    }
}

【讨论】：