我的应用程序在执行时引发异常

Question

这是我的日志猫:

07-01 17:51:51.190 14519-14519/？I/ART:不晚-Enabled-xcheck:jni（已经打开）07-01 17:51:51.290 14519-14519/？D/AndroidRuntime:正在关闭VM 07-01 17:51:51.290 14519-14519/？E/AndroidRuntime:致命异常:主进程:com.exampl.home.AssignmentQues5，PID:14519 java.lang.RuntimeException:无法实例化活动组件InfoCom.exampl.home.AssignmentQues5/com.exampl.home.AssignmentQues5.MainActivity}:java.lang.NullPointerException:尝试在Android.app.ActivityThread.PerformLaunchActivity(ActivityThread.Java:2236)处调用虚拟方法“android.text.Editablescaller.run(zygoteinit.java:903)at com.android.internal.os.zygoteinit.main(zygoteinit.java:698)由以下原因引起:java.lang.NullPointerException:试图在com.exampl.home.assignmentques5.mainactivy.(mainactivy.java:24）at java.lang.reflect.constructor.newinstance(Native method）at java.lang.class.newinstance(Class.Java:1606)at在android.app.activitythread.access800(activitythread.java:151) ；在Android.app.ActivityThread.HandleMessage(ActivityThread.java:1303) ；在android.os.handler.DispatchMessage(handler.java:102) ；在android.os.looper.loop(looper.java:135) ；在android.app.activitythread.main(activitythread.java:5254) ；在java.lang.reflect.Method.invoke(Native Method) ；在java.lang.reflect.method.invoke(Method.java:372) ；在com.android.internal.os.zygoteinitMethodAndArgscaller.run(zygoteinit.java:903) ；网址:com.android.internal.os.zygoteinit.main(zygoteinit.java:698) ；07-01 17:52:00.390 14519-14526/com.exampl.home.assignmentques5 W/ART:挂起所有线程所用时间:180ms 07-01 17:56:51.770 14519-14519/？I/process:发送信号。PID:14519 SIG:9

这是我的Java代码:

package com.exampl.home.assignmentques5;

{
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener
{
    Button b1,b2;
    EditText et1,et2,et3,et4,et5,et6,et7;
    TextView tv1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        b1=(Button)findViewById(R.id.button);
        b2=(Button)findViewById(R.id.button2);
        b1.setOnClickListener(this);
        b2.setOnClickListener(this);
        tv1=(TextView)findViewById(R.id.textView4);
    }
    String s1 = et1.getText().toString();
    String s2 = et2.getText().toString();
    String s3 = et3.getText().toString();
    String s4 = et4.getText().toString();
    String s5 = et5.getText().toString();
    String s6 = et6.getText().toString();
    String s7 = et7.getText().toString();

    int a = Integer.parseInt(s7);

    @Override
    public void onClick(View v)
    { 
        if(v.getId()==R.id.button)
        {
            String S = "Your name is "+s1+" "+s2+" "+s3+"\nYour Address is"+et4+" "+et5+" "+et6+" "+a;
            tv1.setText(S);
        }
        else
        {   et1.setText(" ");
            et2.setText(" ");
            et3.setText(" ");
            et4.setText(" ");
            et5.setText(" ");
            et6.setText(" ");
            et7.setText(" ");

        }

    }
}

Answer 1

这是因为在创建类 时，您试图在 上的 为空。您应该使用 初始化 ，就像使用 方法中的按钮一样。只有这样才能从它们中获取 。

Answer 2

所有这些对象:

EditText et1,et2,et3,et4,et5,et6,et7;

未在onCreated中初始化

因此，在执行此操作之前，您试图获取一个null引用EditText的文本:（最好将其移动到方法内部）

String s1  ;
String s2  ;
String s3  ;
....

在onCreate方法中初始化Wodgets

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    b1=(Button)findViewById(R.id.button);
    b2=(Button)findViewById(R.id.button2);
    b1.setOnClickListener(this);
    b2.setOnClickListener(this);
    tv1=(TextView)findViewById(R.id.textView4);


    //
    et1 = (EditText )findViewById(R.id.????);
    et2 = (EditText )findViewById(R.id.????);
    et3 = (EditText )findViewById(R.id.????);
    ...
   initStrings();
}
private void initStrings(){
  s1 = et1.getText().toString();
  s2 = et2.getText().toString();
  s3 = et3.getText().toString();
  s4 = et4.getText().toString();
  s5 = et5.getText().toString();
  s6 = et6.getText().toString();
  s7 = et7.getText().toString();
}