Android EditText未加载

那么我的应用程序运行正常

一旦我将其添加回：

//final EditText editText = (EditText) findViewById(R.id.editText1);

fragmentactivity无法加载，并在android设备上因错误而终止

final EditText editText = (EditText) findViewById(R.id.editText1);

---

行取消注释，没有任何类型的错误或警告，因此我知道我已经完成了导入…

您必须在

onCreate

方法中放置以下行

            06-13 18:52:07.924: E/Trace(28101): error opening trace file: No such file or directory (2)
            06-13 18:52:08.004: E/AndroidRuntime(28101): FATAL EXCEPTION: main
            06-13 18:52:08.004: E/AndroidRuntime(28101): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.methanegaszonegeolocator/com.example.methanegaszonegeolocator.MainActivity}: java.lang.NullPointerException
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2012)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2113)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at android.app.ActivityThread.access$700(ActivityThread.java:139)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1224)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at android.os.Handler.dispatchMessage(Handler.java:99)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at android.os.Looper.loop(Looper.java:137)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at android.app.ActivityThread.main(ActivityThread.java:4918)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at java.lang.reflect.Method.invokeNative(Native Method)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at java.lang.reflect.Method.invoke(Method.java:511)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
            06-13 18:52:08.004: E/AndroidRuntime(28101):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)

所以在你的情况下，它将是

final EditText editText = (EditText) findViewById(R.id.editText1);

---

这归结为在类实例化时无法调用findViewById

您必须在onCreate方法中调用该行

如果你需要在课堂上的任何地方访问它，那么在课堂的顶端，你应该：

public class MainActivity extends FragmentActivity {

    /**
     * Note that this may be null if the Google Play services APK is not available.
     */
    private GoogleMap mMap;
    final EditText editText; 

    @Override
    protected void onCreate(Bundle arg0) {
        super.onCreate(arg0);
        setContentView(R.layout.activity_main); // PASS YOUR LAYOUT HERE

        editText = (EditText) findViewById(R.id.editText1);
    }

然后在onCreate方法中执行以下操作：

final EditText editText;

final EditText editText;

editText = (EditText) findViewById(R.id.editText1);