Android DatePicker弹出-运行时错误

Question

ADT没有显示警告，但是试图在模拟器上运行它却失败了。

(我修改了一点this code )

public class MainActivity extends Activity {

final Calendar myCalendar = Calendar.getInstance();
final EditText textEdit = (EditText) findViewById(R.id.edit_message);

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

    final DatePickerDialog.OnDateSetListener date = new DatePickerDialog.OnDateSetListener() {

        @Override
        public void onDateSet(DatePicker view, int year, int monthOfYear,
                int dayOfMonth) {
            // TODO Auto-generated method stub
            myCalendar.set(Calendar.YEAR, year);
            myCalendar.set(Calendar.MONTH, monthOfYear);
            myCalendar.set(Calendar.DAY_OF_MONTH, dayOfMonth);
            updateLabel();
        }

    };

    textEdit.setOnClickListener(new OnClickListener() {

        public void onClick(View v ) {
            // TODO Auto-generated method stub
            new DatePickerDialog(MainActivity.this, date, myCalendar
                    .get(Calendar.YEAR), myCalendar.get(Calendar.MONTH),
                    myCalendar.get(Calendar.DAY_OF_MONTH)).show();
        }
    });

}

private void updateLabel() {

    String myFormat = "MM/dd/yy"; //In which you need put here
    SimpleDateFormat sdf = new SimpleDateFormat(myFormat, Locale.US);

    textEdit.setText(sdf.format(myCalendar.getTime()));
}

错误日志：

: W/dalvikvm(2025): threadid=1: thread exiting with uncaught exception (group=0xa86ce648)
: E/AndroidRuntime(2025): FATAL EXCEPTION: main
: E/AndroidRuntime(2025): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.hh_app/com.example.hh_app.MainActivity}: java.lang.NullPointerException
: E/AndroidRuntime(2025):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
: E/AndroidRuntime(2025):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
: E/AndroidRuntime(2025):   at android.app.ActivityThread.access$600(ActivityThread.java:141)
: E/AndroidRuntime(2025):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
: E/AndroidRuntime(2025):   at android.os.Handler.dispatchMessage(Handler.java:99)
: E/AndroidRuntime(2025):   at android.os.Looper.loop(Looper.java:137)
: E/AndroidRuntime(2025):   at android.app.ActivityThread.main(ActivityThread.java:5103)
: E/AndroidRuntime(2025):   at java.lang.reflect.Method.invokeNative(Native Method)
: E/AndroidRuntime(2025):   at java.lang.reflect.Method.invoke(Method.java:525)
: E/AndroidRuntime(2025):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
: E/AndroidRuntime(2025):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
: E/AndroidRuntime(2025):   at dalvik.system.NativeStart.main(Native Method)
: E/AndroidRuntime(2025): Caused by: java.lang.NullPointerException
: E/AndroidRuntime(2025):   at android.app.Activity.findViewById(Activity.java:1853)
: E/AndroidRuntime(2025):   at com.example.hh_app.MainActivity.<init>(MainActivity.java:19)
: E/AndroidRuntime(2025):   at java.lang.Class.newInstanceImpl(Native Method)
: E/AndroidRuntime(2025):   at java.lang.Class.newInstance(Class.java:1130)
: E/AndroidRuntime(2025):   at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
: E/AndroidRuntime(2025):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
: E/AndroidRuntime(2025):   ... 11 more

谢谢。

Answer 1

您需要在setContentView(R.layout.activity_main);之后将editText的赋值移动到onCreate方法中。

textEdit = (EditText) findViewById(R.id.edit_message);

在onCreate()之前，您没有膨胀视图，所以它没有任何地方可以查找您的editText输出。

最后移除。