我的应用程序在执行时抛出异常

Question

这是我的 logcat:

07-01 17:51:51.190 14519-14519/? I/art: Not late-enabling -Xcheck:jni (already on) 07-01 17:51:51.290 14519-14519/? D/AndroidRuntime: Shutting down VM 07-01 17:51:51.290 14519-14519/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.exampl.home.assignmentques5, PID: 14519 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.exampl.home.assignmentques5/com.exampl.home.assignmentques5.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' 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.access0(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.text.Editable android.widget.EditText.getText()' on a null object reference at com.exampl.home.assignmentques5.MainActivity.(MainActivity.java:24) 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.access0(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) 07-01 17:52:00.390 14519-14526/com.exampl.home.assignmentques5 W/art: Suspending all threads took: 180ms 07-01 17:56:51.770 14519-14519/? I/Process: Sending signal. 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

所有这些对象：

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

没有在 onCreated

中初始化

所以您正在尝试获取空引用的文本 EditText 在这样做之前：（最好将其移至方法内部）

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();
}

Answer 2

这是因为您正试图在 EditText 上 getText() 创建 class MainActivity 时的 null。您应该像使用 onCreate 方法中的按钮一样使用 findView 初始化您的 et1, et2, et3。只有这样你才能从他们那里 getText()。

我的应用程序在执行时抛出异常

My application throws an exception upon execution

android

fatal-error

runtimeexception