致命異常主要在Android上運行的應用程序？

Question

我一直在為一個應用程序編程，在我想進行測試時，eclipse Logcat給了我以下日志，但我不知道為什么會發生這種情況，電話和仿真器會顯示“不幸的是您的應用程序已停止”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

這是代碼：

 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:

不勝感激您的幫助！ 謝謝！

Answer 1

杜德，在調用setContentView之后，在onCreate調用所有視圖初始化。 在調用隱式或非super (...)之后立即在構造函數中調用類成員初始化。 您的視圖稍后會在onCreate中創建。

Answer 2

從日志到要重點關注的行是

    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（）不在MainActivity的第36行中找到具有指定視圖的視圖。 檢查此視圖在您的xml布局中是否存在。

Answer 3

很難以格式化的方式閱讀代碼，但看起來這些行

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);

不在任何方法之外，因此它們將在其他任何事物之前被調用，尤其是onCreate() ，其中您調用setContentView()會使它們為null 。

您的Views存在於布局中，因此如果您在調用setContentView()擴大布局之前嘗試對其進行初始化，則它們將返回null 。 一種更常規，更易讀的方式是將它們聲明為成員變量，然后在onCreate()或如果將全都設為setContentView()之后選擇初始化方法中對其進行初始化。 所以看起來可能像

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，此代碼甚至可以編譯嗎？ 還是您只是將其粘貼在這里錯了？

1）您的findViews應該放在setContentView（）之后的onCreate中。

因此，將其添加到您的onCreate中

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，這段代碼在什么地方都不做？

{
    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"));}}:

將此添加到您的btnEnviar的onClick中。