奇怪的错误，android，java.lang.NoClassDefFoundError

public class LOGO_Activity extends BaseActivityExit implements Interface_MyThread {
    SharedPreferences preferences;
    private Editor editor;
    private String usernameStr;
    private String passwordStr;

    Handler handler = new Handler();
    Runnable runnable = new Runnable() {
        @Override
        public void run() {
            // handler自带方法实现定时器
            Intent intent = new Intent(LOGO_Activity.this,MainActivity.class);
            startActivity(intent);
        }
    };

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

        preferences = getSharedPreferences("user_account", this.MODE_PRIVATE);
        editor = preferences.edit();

        usernameStr = preferences.getString("username", "null");
        passwordStr = preferences.getString("password", "null");

        handler.postDelayed(runnable, 2000); // 每隔2s执行

        //new MyThread(LOGO_Activity.this,ServerAPI.system_getAndroidVersionJson, 0).start();
    }```

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没在AndroidMainfest里注册MainActivity？

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看一下MainActivity类出现什么问题