Android Studio 2.1 无法解析符号“R" [英] Android Studio 2.1 Cannot resolve symbol 'R'

问题描述

Android Studio 2.1，Java V8 更新 91，Gradle 2.1.0.

Android Studio 2.1, Java V8 Update 91, Gradle 2.1.0 .

我知道这个问题在这里被问过很多次，但没有一个推荐的解决方案奏效.

I know that this questions has been asked many times here, but none of the recommendation solutions works out.

在编译准备好在模拟器上运行后，我的 IDE 突然在 R.id 属性处给出错误.即使我没有对文件进行任何更改，每个 Java 文件也会突然出现相同的错误.

In a sudden after compiling ready to run on Emulator, my IDE give an error at the R.id attribute. Every Java files suddenly give the same error even I don't make any changes to the file.

我尝试创建一个新项目，看看情况是否有所不同，但错误不断出现.在我看来，这又可能是内部错误.即使我刚刚更新了我的 IDE.

I tried to make a new project, see if things different but the error keep coming. In my mind it could be internal error, again. Even I just update my IDE just now.

Java 文件；

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

    setContentView(R.layout.activity_science);

    list_View = (ListView) findViewById(R.id.maintable); 
    String[] Days = new String[] { "Sunday", "Monday", "Tuesday", "Wednesday","Thursday", "Friday", "Saturday"};
    dayList.addAll(Arrays.asList(Days));
    adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, dayList);
    list_View.setAdapter(adapter);

    NfcAdapter nfc = NfcAdapter.getDefaultAdapter(this);

    if (nfc.isEnabled()) {
        adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, dayList);
        Toast.makeText(this, "NFC turned ON", Toast.LENGTH_SHORT).show();
    }

    else {
        Toast.makeText(this, "Please turn On NFC", Toast.LENGTH_SHORT).show();
    }

}

R 是错误.

与Java相关联的XML文件；

XML file that associate to the Java;

<ListView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/maintable"
    >
</ListView>

这又是一个内部错误吗?

Is this, again, an internal error?

推荐答案

我尝试将 Gradle 版本从 2.1.0 更改为 2.0.0，即使在 AS 版本 2.1 中，也忽略了 Instant Run 性能及其效果.小 R 错误现在消失了.现在，我尝试改回 2.1.0，R 错误也消失了..！！有时这件小事让我有点发疯.

I try to change the Gradle version from 2.1.0 to 2.0.0, even in AS ver 2.1, ignoring the Instant Run performance and its work out. The little R error is now gone. Now, I tried to change back to 2.1.0, the R error also gone..!! Sometime this little thing drive me crazy, a bit.

为我感到羞耻.

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