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已被多次询问，但没有推荐解决方案的解决方案。

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Emulator上运行后，我的IDE突然出现了R.id属性的错误。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.

我试图创建一个新项目，看看是否有什么不同但错误不断涌来。在我看来，这可能是内部错误。即使我刚刚更新我的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 2.1中也是如此，忽略了Instant Run性能及其解决方案。小R错误现在消失了。现在，我试图改回2.1.0，R错误也消失了...... !!
有时这个小东西让我发疯了一点。

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.

对我感到羞耻。

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