Java 在eclipse emulator上运行应用程序时出错

我制作了一个android应用程序，每次我在Emulator中的Eclipse上运行它时，它都会停止。连我都没有错！这是一个非常简单的应用程序。。。但是在模拟器中它崩溃了。我不知道为什么会发生这种情况。在emulator中出现“进程意外停止”或类似的内容

以下是日志：

05-05 09:26:58.699: D/AndroidRuntime(1222): Shutting down VM
05-05 09:26:58.749: W/dalvikvm(1222): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
05-05 09:26:58.819: E/AndroidRuntime(1222): FATAL EXCEPTION: main
05-05 09:26:58.819: E/AndroidRuntime(1222): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.create.namestrings/com.create.namestrings.MainActivity}: java.lang.NullPointerException
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.os.Looper.loop(Looper.java:137)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.ActivityThread.main(ActivityThread.java:5041)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at java.lang.reflect.Method.invokeNative(Native Method)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at java.lang.reflect.Method.invoke(Method.java:511)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at dalvik.system.NativeStart.main(Native Method)
05-05 09:26:58.819: E/AndroidRuntime(1222): Caused by: java.lang.NullPointerException
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.Activity.findViewById(Activity.java:1839)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at com.create.namestrings.MainActivity.<init>(MainActivity.java:16)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at java.lang.Class.newInstanceImpl(Native Method)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at java.lang.Class.newInstance(Class.java:1319)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
05-05 09:26:58.819: E/AndroidRuntime(1222):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
05-05 09:26:58.819: E/AndroidRuntime(1222):     ... 11 more
05-05 09:27:51.169: E/Trace(1263): error opening trace file: No such file or directory (2)

以及舱单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.create.namestrings"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.create.namestrings.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

请帮忙

试试看：

//Rest is the same
EditText etName;
RadioButton RbtnGirl;
RadioButton RbtnBoy;
Button btn;
TextView txt;

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

    etName = (EditText) findViewById (R.id.editText1);
    RbtnGirl = (RadioButton) findViewById (R.id.radioButton1);
    RbtnBoy = (RadioButton) findViewById (R.id.radioButton2);
    btn = (Button) findViewById (R.id.button1);
    txt = (TextView) findViewById (R.id.textView2);
    //Rest is the same

而不是你的代码

---

在

onCreate（）

中使用

btn

时，您收到了

NullPointerException

。这是因为

findViewById（）

在当前扩展的布局中查找视图，该视图在调用

setContentView（）

之前不存在。当您在方法之外初始化视图时，它们都会得到一个空值，因为调用

setContentView（）

的

onCreate（）

尚未被调用。

设置布局内容后，您会发现ID

   private EditText etName;
   private RadioButton RbtnGirl;
   private RadioButton RbtnBoy;
   private Button btn;
   private TextView txt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    etName = (EditText) findViewById (R.id.editText1);
    RbtnGirl = (RadioButton) findViewById (R.id.radioButton1);
    RbtnBoy = (RadioButton) findViewById (R.id.radioButton2);
    btn = (Button) findViewById (R.id.button1);
    txt = (TextView) findViewById (R.id.textView2);
    ......

在将视图设置为布局之前，您正在查找id。因此您得到了NullPointerException

我更新了我的答案，如果按如下操作，您将不得不使文本视图成为最终文本视图，因为您将在单击按钮时使用文本视图。这是不必要的，因此将变量声明为类变量

    setContentView(R.layout.activity_main);
    final Textview txt = (TextView) findViewById (R.id.textView2); 

    setContentView(R.layout.activity_main);
    final Textview txt = (TextView) findViewById (R.id.textView2);