JNI "未定义引用 "到c++方法。

Question

我想在android studio中用JNI创建扑克应用，我想保存一个c++类（TexasHoldem）的实例，并在我写的texasJNI.java中只调用它的方法。

public class jniTexasHoldem {
  private long texasHoldm;
  jniTexasHoldem() {
      ConstructNativeTexas();
  }


  // Used to load the 'native-lib' library on application startup.
  static {
      System.loadLibrary("native-lib");
  }

  /**
   * A native method that is implemented by the 'native-lib' native library,
   * which is packaged with this application.
   */
  private native void ConstructNativeTexas();

  public native String getCardXML();

  public native String stringFromJNI();
}

在mainActivity中:

ublic class MainActivity extends AppCompatActivity {
  private jniTexasHoldem m_TexasHoldem = new jniTexasHoldem();
  ...
  String cardXml = m_TexasHoldem.getCardXML();
}

和native-lib中，

extern "C"
JNIEXPORT jstring JNICALL
Java_android_myapplication_jniTexasHoldem_stringFromJNI(
    JNIEnv* env,
    jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

extern "C"
JNIEXPORT jlong JNICALL
Java_android_myapplication_jniTexasHoldem_ConstructNativeTexas(JNIEnv *env, jobject thiz) {
  TexasHoldm* texasHoldmObj = new TexasHoldm();

  return (jlong)texasHoldmObj;
}

extern "C"
JNIEXPORT jstring JNICALL
Java_android_myapplication_jniTexasHoldem_getCardXML(JNIEnv *env, jobject thiz) {
  jclass c = env->GetObjectClass(thiz);
  // J is the type signature for long:
  jfieldID fid_handle = env->GetFieldID(c, "texasHoldm", "J");
  TexasHoldm * nativeObject = (TexasHoldm *) env->GetLongField(thiz, fid_handle);

  return (env)->NewStringUTF(nativeObject->getCard().c_str());
}

我希望得到自动生成的{card}.png字符串。getCard 方法，但由于 undefined reference to 'TexasHoldm::getCard()'

externalNativeBuild {
    cmake {
        path "src/main/cpp/CMakeLists.txt"
        version "3.10.2"
    }
}
ndkVersion "21.1.6352462"

我在CmakeList中写道："我想用JNI在android studio中创建一个扑克应用

target_link_libraries( # Specifies the target library.
                   native-lib
                   TexasHoldm.h
                   TexasHoldm.cpp
                   PokerTable.h
                   PokerTable.cpp
                   Player.h
                   Player.cpp
                   Hand.h
                   Hand.cpp
                   Card.h
                   Card.cpp


                   # Links the target library to the log library
                   # included in the NDK.
                   ${log-lib} )

Answer 1

所有文件之间都有依赖关系，所以我清理了CMakeLists文件，因为它是一开始就有的（基本的自动生成文件，只有native-lib），我添加了以下内容 ndkVersion "21.1.6352462" 行，并将所有外部.cpp文件添加到了 add_library 部分在CMakeLists文件中。

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             native-lib.cpp **extra .cpp files here**)

所以它把所有的内容都编译在一个外部lib中。