Question

我试图将任何活动的活动传递给使用NDK编写的某些C ++代码。

例如，如果我传递对MainActivity对象的引用（或者可能是SettingsActivity），我如何调用Object类中的getName（）等方法？

如果我声明自己的Java方法＆＃34; giveMeName（）＆＃34;返回getClass.getName（），然后giveMeName（）工作正常但当然它仅限于我声明它的类。如何从C ++代码中调用Object :: getName（） - 而无需修改Java代码以传递Object引用。

编辑：

我以为我有它的工作 - 我看到类名在某些时候被返回，但现在却没有。尝试获取getName（）时，我仍然返回null：

    // PDS: Get the class - should be some sort of Activity subclass..
    jclass clsActivity = pEnv->GetObjectClass( pObj2 );

    if( JNIException( pEnv ) )
      return;

    LogDebugf( "PDS> naNewActivity::clsActivity: %08lx\n", (long) clsActivity );

    if( ! clsActivity )
      return;

    jmethodID mid_getClass = pEnv->GetMethodID( clsActivity, "getClass", "()Ljava/lang/Class;");

    LogDebugf( "PDS> naNewActivity::getClass methodID: %08lx\n", (long) mid_getClass );

    if( JNIException( pEnv ) )
      return;

    // PDS: Call getClass() method on Activity object ( actually Object::getClass() )
    jclass c = (jclass) pEnv->CallObjectMethod( pObj2, mid_getClass );

    LogDebugf( "PDS> naNewActivity::getClass() returns: %08lx\n", (long) c );

    if( JNIException( pEnv ) )
      return;

    // PDS: If we get a Class object, call Class::getName()
    jmethodID mid_getName = pEnv->GetMethodID( c, "getName", "()Ljava/lang/String;");

    LogDebugf( "PDS> naNewActivity::getName methodID: %08lx\n", (long) mid_getName );

*** I AM GETTING null being returned for mid_getName

    if( JNIException( pEnv ) )
      return;

    // PDS: Call method on Activity object ( Object::getName() )
    jobject   n = pEnv->CallObjectMethod( pObj2, mid_getName );

    if( JNIException( pEnv ) )
      return;

    jstring   sName = (jstring) n;

    char *pszData = (char*) pEnv->GetStringUTFChars( sName, JNI_FALSE );

    LogDebugf( "PDS> naNewActivity, class name[%s]\n", pszData );
    pEnv->ReleaseStringUTFChars( sName, pszData );

固定代码：我在下面找到了Seva的帮助：

// PDS: Get the class - should be some sort of Activity subclass..
jclass clsActivity = pEnv->GetObjectClass( pObj2 );

if( JNIException( pEnv ) )
  return;

LogDebugf( "PDS> naNewActivity::clsActivity: %08lx\n", (long) clsActivity );

if( ! clsActivity )
  return;

jmethodID mid_getClass = pEnv->GetMethodID( clsActivity, "getClass", "()Ljava/lang/Class;");

LogDebugf( "PDS> naNewActivity::getClass() methodID: %08lx\n", (long) mid_getClass );

if( JNIException( pEnv ) )
  return;

// PDS: Call getClass() method on Activity object.. ( actually Object::getClass() )
jclass c = (jclass) pEnv->CallObjectMethod( pObj2, mid_getClass );

LogDebugf( "PDS> naNewActivity::getClass() returns: %08lx\n", (long) c );

if( JNIException( pEnv ) )
  return;

jclass clsClass   = pEnv->GetObjectClass( c );

LogDebugf( "PDS> naNewActivity::clsClass: %08lx\n", (long) clsClass );

if( JNIException( pEnv ) )
  return;

// PDS: If we get a Class object, call Class::getName()
jmethodID mid_getName = pEnv->GetMethodID( clsClass, "getName", "()Ljava/lang/String;");

LogDebugf( "PDS> naNewActivity::getName() methodID: %08lx\n", (long) mid_getName );

if( JNIException( pEnv ) )
  return;

// PDS: Can't call method on Activity object - need to call it on its Class (object) ( Class::getName() )
jobject   n = pEnv->CallObjectMethod( c, mid_getName );

if( JNIException( pEnv ) )
  return;

jstring   sName = (jstring) n;

char *pszData = (char*) pEnv->GetStringUTFChars( sName, JNI_FALSE );

LogDebugf( "PDS> naNewActivity, class name[%s]\n", pszData );
pEnv->ReleaseStringUTFChars( sName, pszData );

Answer 1

您不需要修改代码。如果该方法完全可访问，则调用它的代码与在派生类中声明方法时使用的代码相同。

Answer 2

使用java.lang.Object类查找方法ID，然后使用派生类实例的对象指针来调用方法。 JNI允许这样做。首先，您必须按名称找到java.lang.Object的班级ID。

Android JNI：获取父类

2 个答案: