aplicación estrellarse durante el uso de hiladores de moverse a otra actividad

Rabbani Shaik:

Tengo tres hilanderas de manera que tengo que mover a la actividad respetado dependiendo de la entrada en spinners.App se bloquea mientras se ejecuta .i no tienen idea acerca del error. Cualquier ayuda sería appretiated.

He comprobado mi código dos veces y no podía encontrar ningún error La aplicación se bloquea cuando cada vez que trato de ejecutarlo en mi dispositivo.

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
    private Button btn;
    Spinner spin1;
    Spinner spin2;
    Spinner spin3;

    String[] years = {"1", "2", "3", "4"};
    String[] branches = {"CSE", "ECE", "EEE", "CIVIL", "IT", "MECH"};
    String[] sections = {"A", "B", "C"};

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

        Spinner spin1 = (Spinner) findViewById(R.id.spinner1);
        spin1.setOnItemSelectedListener(this);
        ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, years);
        //Drop down layout style - list view with radio button
        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        //attaching dataAdapter to spinner
        spin1.setAdapter(dataAdapter);

        Spinner spin2 = (Spinner) findViewById(R.id.spinner2);
        spin2.setOnItemSelectedListener(this);
        ArrayAdapter<String> dataAdapter2 = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, branches);
        dataAdapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spin2.setAdapter(dataAdapter2);

        Spinner spin3 = (Spinner) findViewById(R.id.spinner3);
        spin3.setOnItemSelectedListener(this);
        ArrayAdapter<String> dataAdapter3 = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, sections);
        dataAdapter3.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spin3.setAdapter(dataAdapter3);

        Button btn = (Button) findViewById(R.id.display);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                displaycheck();
            }
        });
    }

    public void displaycheck() {
        String sp1 = spin1.getSelectedItem().toString();
        String sp2 = spin2.getSelectedItem().toString();
        String sp3 = spin3.getSelectedItem().toString();

        if (sp1.equals("3") && sp2.equals("CSE") && sp3.equals("B")) {
            Intent it = new Intent(this, M2.class);
            startActivity(it);
        }
    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        //on selecting a spinner item
        String item = parent.getItemAtPosition(position).toString();
        Toast.makeText(parent.getContext(), "Selected: " + item, Toast.LENGTH_LONG).show();
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {
    }
}``````
i have expected succesfull opening of other activity, but it`s crashing

**manifest.xml**   `<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.meratimetable">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".M2"></activity>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>    `

**stack trace**

`Process: com.example.meratimetable, PID: 2470
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.widget.Spinner.getSelectedItem()' on a null object reference
        at com.example.meratimetable.MainActivity.displaycheck(MainActivity.java:59)
        at com.example.meratimetable.MainActivity$1.onClick(MainActivity.java:53)
        at android.view.View.performClick(View.java:7339)
        at android.widget.TextView.performClick(TextView.java:14226)
        at android.view.View.performClickInternal(View.java:7305)
        at android.view.View.access$3200(View.java:846)
        at android.view.View$PerformClick.run(View.java:27787)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7081)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
2019-10-18 22:33:14.517 4053-4841/? E/rs$DefaultThreadFactory: ===== Detect pool-thread leak =====
2019-10-18 22:33:14.517 4053-4841/? E/rs$DefaultThreadFactory: dalvik.system.VMStack.getThreadStackTrace(Native Method)`

GensaGames:

Usted sobrescribir los elementos de los estados de actividad. Cambiar su Spinningdeclaración a la siguiente.

Desde:

    Spinner spin1 = (Spinner) findViewById(R.id.spinner1);

A:

    spin1 = (Spinner) findViewById(R.id.spinner1);