致命异常主要在Android上运行应用程序？

Question

我一直在编写一个应用程序，当时我想进行测试，eclipse Logcat给了我以下日志我不知道为什么会发生这种情况，手机和模拟器给出“不幸的是你的应用程序停止了“消息：

07-26 19:47:03.880: W/dalvikvm(834): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
07-26 19:47:03.910: E/AndroidRuntime(834): FATAL EXCEPTION: main
07-26 19:47:03.910: E/AndroidRuntime(834): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.xanmaya.kapschfinal/com.xanmaya.kapschfinal.MainActivity}: java.lang.NullPointerException
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.os.Handler.dispatchMessage(Handler.java:99)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.os.Looper.loop(Looper.java:137)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.ActivityThread.main(ActivityThread.java:5041)
07-26 19:47:03.910: E/AndroidRuntime(834):  at java.lang.reflect.Method.invokeNative(Native Method)
07-26 19:47:03.910: E/AndroidRuntime(834):  at java.lang.reflect.Method.invoke(Method.java:511)
07-26 19:47:03.910: E/AndroidRuntime(834):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-26 19:47:03.910: E/AndroidRuntime(834):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-26 19:47:03.910: E/AndroidRuntime(834):  at dalvik.system.NativeStart.main(Native Method)
07-26 19:47:03.910: E/AndroidRuntime(834): Caused by: java.lang.NullPointerException
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.Activity.findViewById(Activity.java:1839)
07-26 19:47:03.910: E/AndroidRuntime(834):  at com.xanmaya.kapschfinal.MainActivity.<init>(MainActivity.java:36)
07-26 19:47:03.910: E/AndroidRuntime(834):  at java.lang.Class.newInstanceImpl(Native Method)
07-26 19:47:03.910: E/AndroidRuntime(834):  at java.lang.Class.newInstance(Class.java:1319)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
07-26 19:47:03.910: E/AndroidRuntime(834):  ... 11 more

以下是代码：

 package com.xanmaya.kapschfinal;

import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;

public class MainActivity extends Activity {

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

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);


Button btnEnviar = (Button) findViewById(R.id.btnEnviar);
btnEnviar.setOnClickListener(new View.OnClickListener() { 
@Override
public void onClick(View v) {
    }}
);
return true;

}
EditText etModulo = (EditText) findViewById(R.id.etModulo);
EditText etAmpli = (EditText) findViewById(R.id.etAmpli);
EditText etAntena = (EditText) findViewById(R.id.etAntena);
EditText etCable = (EditText) findViewById(R.id.etCable);
EditText etFecha = (EditText) findViewById(R.id.etFecha);
EditText etlugar = (EditText) findViewById(R.id.etlugar);
EditText etenvia = (EditText) findViewById(R.id.etenvia);
CheckBox checkampli = (CheckBox) findViewById(R.id.checkampli);
CheckBox checkantena = (CheckBox) findViewById(R.id.checkantena);
CheckBox checkmodulo = (CheckBox) findViewById(R.id.checkmodulo);
CheckBox checkcable = (CheckBox) findViewById(R.id.checkcable);

{
    Intent emailIntent = new Intent(Intent.ACTION_SENDTO);
emailIntent.setData(Uri.parse("mailto:"));
emailIntent.putExtra(Intent.EXTRA_EMAIL, "villasantdesign@gmail.com");
emailIntent.putExtra(Intent.EXTRA_SUBJECT, "Resumen");
emailIntent.putExtra(Intent.EXTRA_TEXT, etModulo.getText()); etAntena.getText(); etCable.getText(); etlugar.getText(); etFecha.getText(); etAmpli.getText();}{;
Intent emailIntent = new Intent(Intent.ACTION_SENDTO);
emailIntent.setType("message/rfc822");
startActivity(Intent.createChooser(emailIntent, "btnEnviar"));}}`code:

感谢您的帮助！谢谢！

Answer 1

Dude，在调用setContentView后调用onCreate中的所有视图初始化。在调用隐式或非super (...)之后立即在构造函数中调用类成员初始化。您的视图将在稍后的onCreate中创建。

Answer 2

要关注的日志中的行是

    07-26 19:47:03.910: E/AndroidRuntime(834): Caused by: java.lang.NullPointerException
    07-26 19:47:03.910: E/AndroidRuntime(834):  at android.app.Activity.findViewById(Activity.java:1839)
    07-26 19:47:03.910: E/AndroidRuntime(834):  at com.xanmaya.kapschfinal.MainActivity.<init>(MainActivity.java:36)

findViewById（）没有在MainActivity的第36行找到具有指定View的视图。检查此视图是否存在于xml布局中。

Answer 3

很难按照格式化的方式阅读您的代码，但似乎这些行

EditText etModulo = (EditText) findViewById(R.id.etModulo);
EditText etAmpli = (EditText) findViewById(R.id.etAmpli);
EditText etAntena = (EditText) findViewById(R.id.etAntena);
EditText etCable = (EditText) findViewById(R.id.etCable);
EditText etFecha = (EditText) findViewById(R.id.etFecha);
EditText etlugar = (EditText) findViewById(R.id.etlugar);
EditText etenvia = (EditText) findViewById(R.id.etenvia);
CheckBox checkampli = (CheckBox) findViewById(R.id.checkampli);
CheckBox checkantena = (CheckBox) findViewById(R.id.checkantena);
CheckBox checkmodulo = (CheckBox) findViewById(R.id.checkmodulo);
CheckBox checkcable = (CheckBox) findViewById(R.id.checkcable);

不在任何方法之内，因此他们会在其他任何方法之前被调用，尤其是onCreate()，您可以调用setContentView()来null。

您的Views存在于您的布局中，因此如果您在通过调用null来扩充布局之前尝试初始化它们，它们将返回setContentView()。一种更传统的方式，更可读的方式是将它们声明为成员变量，然后在onCreate()或初始化方法中初始化它们，如果您选择AFTER all to setContentView()。所以它可能看起来像

public class MainActivity extends Activity {

    EditText etModulo;   // you can declare them as member variables here so they can be used anywhere in the class
    EditText etAmpli; 
    EditText etAntena; 

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

    etModulo = (EditText) findViewById(R.id.etModulo);   // but initialize them here after inflating your layout
    etAmpli = (EditText) findViewById(R.id.etAmpli);
    etAntena = (EditText) findViewById(R.id.etAntena);

}

Answer 4

首先，这个代码甚至可以编译吗？或者你只是把它贴在这里错了？

1）你的findViews应该在你的setContentView（）之后进入onCreate。

所以在你的onCreate中添加它

EditText etModulo = (EditText) findViewById(R.id.etModulo);
EditText etAmpli = (EditText) findViewById(R.id.etAmpli);
EditText etAntena = (EditText) findViewById(R.id.etAntena);
EditText etCable = (EditText) findViewById(R.id.etCable);
EditText etFecha = (EditText) findViewById(R.id.etFecha);
EditText etlugar = (EditText) findViewById(R.id.etlugar);
EditText etenvia = (EditText) findViewById(R.id.etenvia);
CheckBox checkampli = (CheckBox) findViewById(R.id.checkampli);
CheckBox checkantena = (CheckBox) findViewById(R.id.checkantena);
CheckBox checkmodulo = (CheckBox) findViewById(R.id.checkmodulo);
CheckBox checkcable = (CheckBox) findViewById(R.id.checkcable);

2）此外，这个代码在不知名的地方做了什么？

{
    Intent emailIntent = new Intent(Intent.ACTION_SENDTO);
    emailIntent.setData(Uri.parse("mailto:"));
    emailIntent.putExtra(Intent.EXTRA_EMAIL, "villasantdesign@gmail.com");
    emailIntent.putExtra(Intent.EXTRA_SUBJECT, "Resumen");
    emailIntent.putExtra(Intent.EXTRA_TEXT, etModulo.getText()); etAntena.getText(); etCable.getText(); etlugar.getText(); etFecha.getText(); etAmpli.getText();}{;
    Intent emailIntent = new Intent(Intent.ACTION_SENDTO);
    emailIntent.setType("message/rfc822");
    startActivity(Intent.createChooser(emailIntent, "btnEnviar"));}}:

将此内容添加到btnEnviar的onClick中。