只是尝试我的第二个应用程序，但收到错误消息“不幸的是您的应用程序已停止”。

Question

package com.example.medreminder;

import androidx.appcompat.app.AppCompatActivity;``

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

    public class MainActivity extends AppCompatActivity {

   String MedecineName;
   int DailyDozage , NoOfPiecesBought;

   EditText medecinename;
   EditText dailydozage;
   EditText noofpiecesbought;

   Button submitbutton = (Button) findViewById(R.id.submitbutton);





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

      medecinename = (EditText) findViewById(R.id.medecinename);
      dailydozage = (EditText) findViewById(R.id.dailydozage);
      noofpiecesbought = (EditText) findViewById(R.id.noofpiecesbought);

      submitbutton = findViewById(R.id.submitbutton);
      submitbutton = (Button) findViewById(R.id.submitbutton);
      submitbutton.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
             MedecineName = medecinename.getText().toString();
             DailyDozage =Integer.valueOf(dailydozage.getText().toString());
             NoOfPiecesBought = Integer.valueOf(noofpiecesbought.getText().toString());


            showToast(MedecineName);
            showToast(String.valueOf(DailyDozage));
            showToast(String.valueOf( NoOfPiecesBought));

        }
    });
}

private void showToast(String Text)
{
    Toast.makeText(MainActivity.this, Text , Toast.LENGTH_SHORT).show();
}

}

__________________________________________ LOGCAT ________________________________________________________________________________________________________________________________________________________________________________________________

03-13 17：44：04.993 5251-5256 /？电子/艺术：无法向调试器发送回复：管道损坏03-13 17：44：05.075 5251-5251 /？ E / AndroidRuntime：致命异常：main流程：com.example.medreminder，PID：5251java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.medreminder / com.example.medreminder.MainActivity}：java.lang.NullPointerException：尝试调用虚拟方法'void android.widget.Button.setOnClickListener（android。 view.View $ OnClickListener）'上的空对象引用在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2416）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2476）在android.app.ActivityThread.-wrap11（ActivityThread.java）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1344）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:148）在android.app.ActivityThread.main（ActivityThread.java:5417）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:726）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:616）原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.Button.setOnClickListener（android.view.View $ OnClickListener）'在com.example.medreminder.MainActivity.onCreate（MainActivity.java:36）在android.app.Activity.performCreate（Activity.java:6237）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1107）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2369）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2476）在android.app.ActivityThread.-wrap11（ActivityThread.java）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1344）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:148）在android.app.ActivityThread.main（ActivityThread.java:5417）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:726）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:616）。

package com.example.medreminder; import androidx.appcompat.app.AppCompatActivity;``导入android.os.Bundle;导入android.view.View;导入android.widget.Button;导入android.widget.EditText; ...

Answer 1

您正在尝试在空对象引用上调用setOnClickListener。您的submitbutton指的是null。