java - TextWatcher 在启动后关闭我的应用程序

Question

自从我开始使用 TextWatcher 以来，我的应用程序不断崩溃...正如你在下面看到的，我为 3 个 EditText 字段创建了一个 TextWatcher...我做了一个按钮来监听 3 个 EditText..如果它们为空，则按钮将被禁用。当字段被填充时，按钮应该被启用..

 package com.example.magazijnapp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.MenuPopupWindow;

import android.content.DialogInterface;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.SpinnerAdapter;
import android.widget.Switch;
import android.widget.TextView;
import android.widget.Toast;

import org.w3c.dom.Text;

import java.sql.Array;

public class MainActivity extends AppCompatActivity {

    Spinner spinnermagazijn;
    Button knop;
    private EditText EditTextregisternummerbalk;
    private EditText EditTextticketnummerbalk;
    private EditText EditTextartikelnummerbalk;
    private Button knopconfirm;




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

        EditTextregisternummerbalk = findViewById(R.id.registernummerbalk);
        EditTextticketnummerbalk = findViewById(R.id.ticketnummerbalk);
        EditTextartikelnummerbalk = findViewById(R.id.artikelnummerbalk);
        knopconfirm = findViewById(R.id.knop);

        EditTextregisternummerbalk.addTextChangedListener(invulTextWatcher);
        EditTextticketnummerbalk.addTextChangedListener(invulTextWatcher);
        EditTextartikelnummerbalk.addTextChangedListener(invulTextWatcher);
    }
        private TextWatcher invulTextWatcher = new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                String registernummerinput = EditTextregisternummerbalk.getText().toString().trim();
                String ticketnummerinput = EditTextticketnummerbalk.getText().toString().trim();
                String artikelnummerinput = EditTextartikelnummerbalk.getText().toString().trim();

                knopconfirm.setEnabled(!registernummerinput.isEmpty() && !ticketnummerinput.isEmpty() &&! artikelnummerinput.isEmpty());
            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        };
    {

        spinnermagazijn = findViewById(R.id.spinnermagazijn);

        knop = findViewById(R.id.knop);
        populatespinnermagazijn();


        // Dit is het stukje voor de Knop afboeken waarmee je een melding genereerd,  String aanpassen voor ander resultaat.
        knop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            Toast.makeText(MainActivity.this, (R.string.succes), Toast.LENGTH_SHORT) .show();
            }

        });


    }
        // Dit gedeelte is voor de spinner.
    private void populatespinnermagazijn() {
        ArrayAdapter<String> magazijnenAdapter  = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, getResources().getStringArray(R.array.steunpunten));
        magazijnenAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinnermagazijn.setAdapter(magazijnenAdapter);
    }
}

这是我的 logcat...

03-19 21:04:06.293 21151-21151/? E/libprocessgroup: failed to make and chown /acct/uid_10060: Read-only file system
03-19 21:04:06.293 21151-21151/? W/Zygote: createProcessGroup failed, kernel missing CONFIG_CGROUP_CPUACCT?
03-19 21:04:06.293 21151-21151/? I/art: Not late-enabling -Xcheck:jni (already on)
03-19 21:04:06.313 21151-21161/? I/art: Debugger is no longer active
03-19 21:04:06.351 21151-21151/? D/AndroidRuntime: Shutting down VM
03-19 21:04:06.354 21151-21151/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.magazijnapp, PID: 21151
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.magazijnapp/com.example.magazijnapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
        at android.app.ActivityThread.access$800(ActivityThread.java:151)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:149)
        at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:99)
        at android.content.Context.obtainStyledAttributes(Context.java:437)
        at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:692)
        at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:659)
        at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:479)
        at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:214)
        at com.example.magazijnapp.MainActivity.<init>(MainActivity.java:73)
        at java.lang.reflect.Constructor.newInstance(Native Method)
        at java.lang.Class.newInstance(Class.java:1606)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1066)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
        at android.app.ActivityThread.access$800(ActivityThread.java:151) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:135) 
        at android.app.ActivityThread.main(ActivityThread.java:5254) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:372) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
03-19 21:04:07.996 21151-21151/? I/Process: Sending signal. PID: 21151 SIG: 9

Answer 1

有两个findViewById(R.id.knop);

删除这一行:

knop = findViewById(R.id.knop);

并更改:

knopconfirm.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
        Toast.makeText(MainActivity.this, (R.string.succes), Toast.LENGTH_SHORT) .show();
        }

    });