Android - 无法解析符号“R”答案

【问题标题】：Android - Cannot resolve symbol "R"Android - 无法解析符号“R”
【发布时间】：2015-04-23 04:18:19
【问题描述】：

许多关于 stackoverflow 的回复建议导入 R。我这样做了，并且在问这个问题之前，我确保重建/清理我的路径超过 10 次。

以下是我的文件的排列方式：

我们都可以清楚地看到错误位于MainActivity 文件或 XML 文件之间。

这是 MainActivity 文件的代码，它几乎是 Google 的 git hub 帐户的副本，唯一的错误是它无法识别“R”是什么。：

    package com.eatwithme;

/*
 * Copyright (C) 2015 Google Inc. All Rights Reserved.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

import android.content.res.Resources;
import android.net.Uri;
import android.os.Bundle;
import android.text.Html;
import android.text.Spanned;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import com.eatwithme.activities.SampleActivityBase;
import com.eatwithme.logger.Log;
import com.eatwithme.R;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.PendingResult;
import com.google.android.gms.common.api.ResultCallback;
import com.google.android.gms.location.places.Place;
import com.google.android.gms.location.places.PlaceBuffer;
import com.google.android.gms.location.places.Places;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.LatLngBounds;



public class MainActivity extends SampleActivityBase
        implements GoogleApiClient.OnConnectionFailedListener, GoogleApiClient.ConnectionCallbacks {

    /**
     * GoogleApiClient wraps our service connection to Google Play Services and provides access
     * to the user's sign in state as well as the Google's APIs.
     */
    protected GoogleApiClient mGoogleApiClient;

    private PlaceAutocompleteAdapter mAdapter;

    private AutoCompleteTextView mAutocompleteView;
    private TextView mPlaceDetailsText;

    private static final LatLngBounds BOUNDS_GREATER_SYDNEY = new LatLngBounds(
            new LatLng(-34.041458, 150.790100), new LatLng(-33.682247, 151.383362));

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Set up the Google API Client if it has not been initialised yet.
        if (mGoogleApiClient == null) {
            rebuildGoogleApiClient();
        }

        setContentView(R.layout.activity_main);

        // Retrieve the AutoCompleteTextView that will display Place suggestions.
        mAutocompleteView = (AutoCompleteTextView)
                findViewById(R.id.autocomplete_places);

        // Register a listener that receives callbacks when a suggestion has been selected
        mAutocompleteView.setOnItemClickListener(mAutocompleteClickListener);

        // Retrieve the TextView that will display details of the selected place.
        mPlaceDetailsText = (TextView) findViewById(R.id.place_details);

        // Set up the adapter that will retrieve suggestions from the Places Geo Data API that cover
        // the entire world.
        mAdapter = new PlaceAutocompleteAdapter(this, android.R.layout.simple_list_item_1,
                BOUNDS_GREATER_SYDNEY, null);
        mAutocompleteView.setAdapter(mAdapter);

        // Set up the 'clear text' button that clears the text in the autocomplete view
        Button clearButton = (Button) findViewById(R.id.button_clear);
        clearButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mAutocompleteView.setText("");
            }
        });
    }

    /**
     * Listener that handles selections from suggestions from the AutoCompleteTextView that
     * displays Place suggestions.
     * Gets the place id of the selected item and issues a request to the Places Geo Data API
     * to retrieve more details about the place.
     *
     * @see com.google.android.gms.location.places.GeoDataApi#getPlaceById(com.google.android.gms.common.api.GoogleApiClient,
     * String...)
     */
    private AdapterView.OnItemClickListener mAutocompleteClickListener
            = new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            /*
             Retrieve the place ID of the selected item from the Adapter.
             The adapter stores each Place suggestion in a PlaceAutocomplete object from which we
             read the place ID.
              */
            final PlaceAutocompleteAdapter.PlaceAutocomplete item = mAdapter.getItem(position);
            final String placeId = String.valueOf(item.placeId);
            Log.i(TAG, "Autocomplete item selected: " + item.description);

            /*
             Issue a request to the Places Geo Data API to retrieve a Place object with additional
              details about the place.
              */
            PendingResult<PlaceBuffer> placeResult = Places.GeoDataApi
                    .getPlaceById(mGoogleApiClient, placeId);
            placeResult.setResultCallback(mUpdatePlaceDetailsCallback);

            Toast.makeText(getApplicationContext(), "Clicked: " + item.description,
                    Toast.LENGTH_SHORT).show();
            Log.i(TAG, "Called getPlaceById to get Place details for " + item.placeId);
        }
    };

    /**
     * Callback for results from a Places Geo Data API query that shows the first place result in
     * the details view on screen.
     */
    private ResultCallback<PlaceBuffer> mUpdatePlaceDetailsCallback
            = new ResultCallback<PlaceBuffer>() {
        @Override
        public void onResult(PlaceBuffer places) {
            if (!places.getStatus().isSuccess()) {
                // Request did not complete successfully
                Log.e(TAG, "Place query did not complete. Error: " + places.getStatus().toString());

                return;
            }
            // Get the Place object from the buffer.
            final Place place = places.get(0);

            // Format details of the place for display and show it in a TextView.
            mPlaceDetailsText.setText(formatPlaceDetails(getResources(), place.getName(),
                    place.getId(), place.getAddress(), place.getPhoneNumber(),
                    place.getWebsiteUri()));

            Log.i(TAG, "Place details received: " + place.getName());
        }
    };

    private static Spanned formatPlaceDetails(Resources res, CharSequence name, String id,
                                              CharSequence address, CharSequence phoneNumber, Uri websiteUri) {
        Log.e(TAG, res.getString(R.string.place_details, name, id, address, phoneNumber,
                websiteUri));
        return Html.fromHtml(res.getString(R.string.place_details, name, id, address, phoneNumber,
                websiteUri));

    }


    /**
     * Construct a GoogleApiClient for the {@link Places#GEO_DATA_API} using AutoManage
     * functionality.
     * This automatically sets up the API client to handle Activity lifecycle events.
     */
    protected synchronized void rebuildGoogleApiClient() {
        // When we build the GoogleApiClient we specify where connected and connection failed
        // callbacks should be returned, which Google APIs our app uses and which OAuth 2.0
        // scopes our app requests.
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .enableAutoManage(this, 0 /* clientId */, this)
                .addConnectionCallbacks(this)
                .addApi(Places.GEO_DATA_API)
                .build();
    }

    /**
     * Called when the Activity could not connect to Google Play services and the auto manager
     * could resolve the error automatically.
     * In this case the API is not available and notify the user.
     *
     * @param connectionResult can be inspected to determine the cause of the failure
     */
    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {

        Log.e(TAG, "onConnectionFailed: ConnectionResult.getErrorCode() = "
                + connectionResult.getErrorCode());

        // TODO(Developer): Check error code and notify the user of error state and resolution.
        Toast.makeText(this,
                "Could not connect to Google API Client: Error " + connectionResult.getErrorCode(),
                Toast.LENGTH_SHORT).show();

        // Disable API access in the adapter because the client was not initialised correctly.
        mAdapter.setGoogleApiClient(null);

    }


    @Override
    public void onConnected(Bundle bundle) {
        // Successfully connected to the API client. Pass it to the adapter to enable API access.
        mAdapter.setGoogleApiClient(mGoogleApiClient);
        Log.i(TAG, "GoogleApiClient connected.");

    }

    @Override
    public void onConnectionSuspended(int i) {
        // Connection to the API client has been suspended. Disable API access in the client.
        mAdapter.setGoogleApiClient(null);
        Log.e(TAG, "GoogleApiClient connection suspended.");
    }

}

另外，这是我的 Android 清单文件（已删除我的密钥）。请注意我的活动名称。我这样做是因为如果我删除活动名称前的com.eatwithme，它会给我一个错误。

    <?xml version="1.0" encoding="UTF-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.google.playservices.placecomplete"
    android:versionCode="1"
    android:versionName="1.0">
<uses-sdk
    android:minSdkVersion="14"
    android:targetSdkVersion="19"/>

<!-- PlacePicker also requires OpenGL ES version 2 -->
<uses-feature
    android:glEsVersion="0x00020000"
    android:required="true"/>

<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>

<application
    android:allowBackup="true"
    android:label="@string/app_name"
    android:icon="@mipmap/ic_launcher"
    android:theme="@style/AppTheme">

    <meta-data
        android:name="com.google.android.gms.version"
        android:value="@integer/google_play_services_version"/>

    <meta-data
        android:name="com.google.android.geo.API_KEY"
        android:value="AnLE"/>

    <activity
        android:name="com.eatwithme.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>

我个人已经尽力了，但遗憾的是，我无法解决这个冲突。在我看来，唯一的三个错误来源可能是

1) 没有 R 文件

2) AndoridManifest 文件不对

3) 主文件不正确 4) 文件顺序不对

关于这个问题的任何指导？

【问题讨论】：

标签： java android xml android-activity

【解决方案1】：

问题在于您的 xml 清单：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
Wrong --> package="com.example.google.playservices.placecomplete"
android:versionCode="1"
android:versionName="1.0">

它必须是您项目的确切包名称，即：

package="com.eatwithme"

不是 google 示例包名称。

【讨论】：

老实说，在同一个文件上工作了 8 多个小时后，我很惭愧我没有注意到那个错误。谢谢：D
让我看看是否解决了它（希望应该）
你是我的救星！我为自己的错误感到非常羞耻哈哈！我会尽快接受您的回答！ :)

【解决方案2】：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.google.playservices.placecomplete"

将此包名称更改为您的包名称，即 com.eatwithme 包。

【讨论】：

【解决方案3】：

我没有通读您的所有代码 - 抱歉 :)

我建议删除您对 R 的导入。如果您确定所有文件都在正确的位置，请按照 @Abhishekvasisht 的建议和“清理项目”执行（在 Android Studio 中，您单击构建 > 清理项目；我忘记了在哪里它在 Eclipse 中）。

如果这不起作用，您还可以尝试所谓的“使缓存无效并重新启动”。这有点极端，因为它摆脱了项目的本地历史，但听起来你已经到了绝望的地步。在 Android Studio 中，您单击 File > Invalidate Caches / Restart... 并且您想要选择在同一操作中使所有内容无效并重新启动的选项。

作为最后的手段，您可以尝试将现有代码作为新的 Android 项目导入。这是一个废话拍摄，但过去它对我有用过几次。

祝你好运！对不起，伙计，我知道这会是多么令人沮丧。

【讨论】：

【解决方案4】：

如果您是 udacity android 应用程序开发和学习课程 2A/5th 主题的初学者，并且在运行 MainActivity.java 代码编译时出现问题，则将以下代码放入 MainActivity.java 代码如下

 package com.example.android.justjava;
    import android.support.v7.app.ActionBarActivity;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.view.View;
    import android.widget.TextView;
public class MainActivity extends ActionBarActivity {

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

        public void submitOrder(View view) {
            display(1);
        }
        private void display(int number) {
            TextView quantityTextView = (TextView) findViewById(
                    R.id.quanity_text_view);
            quantityTextView.setText("" + number);
        }
        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.menu_main, menu);
            return true;
        }

        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
            // Handle action bar item clicks here. The action bar will
            // automatically handle clicks on the Home/Up button, so long
            // as you specify a parent activity in AndroidManifest.xml.
            int id = item.getItemId();

            //noinspection SimplifiableIfStatement
            if (id == R.id.action_settings) {
                return true;
            }

            return super.onOptionsItemSelected(item);
        }
    }

【讨论】：

【解决方案5】：

我没有足够的引用来添加 cmets，否则这将是一个评论。

根据我的个人经验，尝试“清理并重建”，这有时会清除此错误。

希望其他人可以支持我

【讨论】：

恐怕我这样做了超过 10 次。在过去的两个小时里，这就是我所做的一切，因为我几乎迷路了。不过谢谢你的建议！ :D

【解决方案6】：

确保您的所有 XML 文件都具有有效的资源、图像和内容以及清理项目。

我从 GitBucket 更新了我的项目，但不知何故丢失了一个 .png，所以我得到了那个错误并且 R 丢失了。我专注于解决 R 问题并为此浪费了几个小时，当我将随机的 .png 替换为丢失的一个并清理项目时，R 又回来了。

【讨论】：

【解决方案7】：

迟到的答案，另一种解决方案。认为有人需要它。

我使用的是 gradle 3.3.0。这是罪魁祸首。浪费了我生命中的 6.50 小时。 Gradle 3.2.1 消除了这个错误。

classpath 'com.android.tools.build:gradle:3.2.1'

【讨论】：

【解决方案8】：

我遇到了同样的问题。我的解决方案是我保存项目的目录路径太长。

【讨论】：