尝试在 null object 引用上调用虚拟方法并设置点击侦听器

Question

I am trying to have a button within a popup send a variable to another class. However, when setting the on click listener I get this issue. I have initialized the button and tried to move the code to a different location. I have removed some of the code after the issue as it is not relevant

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import android.Manifest;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Context;
import android.content.pm.PackageManager;
import android.hardware.camera2.*;
import android.os.Bundle;
import android.view.*;
import android.util.*;
import android.widget.*;
import java.math.*;


public class MainActivity extends AppCompatActivity {

    ImageButton imageButton, singleImageButton;
    Integer width, height, minISO, maxISO, ISO, numberImages;
    boolean focusable;
    View popupView;
    LayoutInflater inflater;
    SeekBar ISOseekbar, exposureBar;
    TextView ISOreadout, exposureReadout, textView;
    String cameraId, numberImagesString;
    Range<Integer> rangeISO;
    Range<Long> exposureRange;
    Long exposureMax, exposureMin, exposure;
    BigDecimal exposureRoundedMax, exposureRoundedMin;
    Button acceptNumberImages;
    EditText numberImagesInput;


    public void mainUI(){

        setContentView(R.layout.activity_main);
        imageButton = findViewById(R.id.imageButton);
        imageButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                inflater = (LayoutInflater)
                        getSystemService(LAYOUT_INFLATER_SERVICE);
                popupView = inflater.inflate(R.layout.cameralayout, null);
                width = LinearLayout.LayoutParams.WRAP_CONTENT;
                height = LinearLayout.LayoutParams.WRAP_CONTENT;
                focusable = true;
                final PopupWindow popupwindow = new PopupWindow(popupView, width, height, focusable);
                popupwindow.showAtLocation(view, Gravity.CENTER, 0, 0);
                acceptNumberImages = findViewById(R.id.acceptNumberImages);
                acceptNumberImages.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        numberImagesInput = findViewById(R.id.numberImagesInput);
                        numberImagesString = numberImagesInput.getText().toString();
                        numberImages = Integer.parseInt(numberImagesString);
                        takePhoto.multipleImages(numberImages);

                    }
                });
                popupView.setOnTouchListener(new View.OnTouchListener() {
                    @Override
                    public boolean onTouch(View v, MotionEvent event) {
                        popupwindow.dismiss();
                        return true;
                    }
                });

            }

        });

The full error that I get is:

    Process: com.example.startrailscamera, PID: 18190
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.example.startrailscamera.MainActivity$1.onClick(MainActivity.java:52)
        at android.view.View.performClick(View.java:6608)
        at android.view.View.performClickInternal(View.java:6585)
        at android.view.View.access$3100(View.java:785)
        at android.view.View$PerformClick.run(View.java:25921)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:201)
        at android.app.ActivityThread.main(ActivityThread.java:6861)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)

Answer 1

Try changing acceptNumberImages = findViewById(R.id.acceptNumberImages) to acceptNumberImages = popupView.findViewById(R.id.acceptNumberImages) if acceptNumberImages is a view in your cameralayout.xml file.

Answer 2

1. Have you tryed to put the setOnClickListener outside the other setOnClickListener?
2. Are u sure the "findViewById(R.id.acceptNumberImages);" aren't returning null?