java–Android First App教程问题

我一直试图让它工作,甚至完全按照教程的说法复制和粘贴代码,但它似乎不起作用.我知道问题出在MainActivity或displayMessageActivity中,但我看不出有什么问题.我还将displayMessageActivity与MainActivity放在同一个文件夹中.

我收到以下错误.

displayMessageActivityGradle: error: cannot find symbol class SuppresslintGradle: error: package R does not existGradle: error: cannot find symbol variable NavUtilsMainActivityGradle: error: cannot find symbol class displayMessageActivity

我已经习惯了一段时间,并且无法弄清楚我做错了什么.任何帮助深表感谢.

是)我有的,

AndroIDManifest.xml中

~snip~        

DisplayMessageActivity

import android.app.Activity;import android.os.Build;import android.os.Bundle;import android.view.MenuItem;public class DisplayMessageActivity extends Activity {    @SuppressLint("NewApi")    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_display_message);        // Make sure we're running on Honeycomb or higher to use ActionBar APIs        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {            // Show the Up button in the action bar.            getActionBar().setDisplayHomeAsUpEnabled(true);        }    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        switch (item.getItemId()) {            case android.R.id.home:                NavUtils.navigateUpFromSameTask(this);                return true;        }        return super.onOptionsItemSelected(item);    }}

主要活动

package com.example.myfirstapp;import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.view.Menu;import android.view.View;import android.widget.EditText;public class MainActivity extends Activity {    public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";    @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);        return true;    }    public void sendMessage(View view) {        Intent intent = new Intent(this,DisplayMessageActivity.class);        EditText editText = (EditText) findViewById(R.id.edit_message);        String message = editText.getText().toString();        intent.putExtra(EXTRA_MESSAGE,message);        startActivity(intent);    }}

UPDATE

Juned和Peter是对的.它不能立即工作的唯一原因是因为我弄乱了其他东西.多谢你们！

import android.annotation.SuppressLint;import android.support.v4.app.NavUtils;

compile 'com.android.support:support-v4:18.0.+'