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SDL_AndroidGetActivity

Retrieve the Java instance of the Android activity class.

Syntax

void * SDL_AndroidGetActivity(void);

Return Value

Returns the jobject representing the instance of the Activity class of the Android application, or NULL on error.

Remarks

The prototype of the function in SDL's code actually declares a void* return type, even if the implementation returns a jobject. The rationale being that the SDL headers can avoid including jni.h.

The jobject returned by the function is a local reference and must be released by the caller. See the PushLocalFrame() and PopLocalFrame() or DeleteLocalRef() functions of the Java native interface:

https://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/functions.html

Version

This function is available since SDL 2.0.0.

Code Examples

#include "SDL.h"
#include <jni.h>

// This example requires C++ and a custom Java method named "void showHome()"

// Calls the void showHome() method of the Java instance of the activity.
void showHome(void)
{
    // retrieve the JNI environment.
    JNIEnv* env = (JNIEnv*)SDL_AndroidGetJNIEnv();

    // retrieve the Java instance of the SDLActivity
    jobject activity = (jobject)SDL_AndroidGetActivity();

    // find the Java class of the activity. It should be SDLActivity or a subclass of it.
    jclass clazz(env->GetObjectClass(activity));

    // find the identifier of the method to call
    jmethodID method_id = env->GetMethodID(clazz, "showHome", "()V");

    // effectively call the Java method
    env->CallVoidMethod(activity, method_id);

    // clean up the local references.
    env->DeleteLocalRef(activity);
    env->DeleteLocalRef(clazz);

    // Warning (and discussion of implementation details of SDL for Android):
    // Local references are automatically deleted if a native function called
    // from Java side returns. For SDL this native function is main() itself.
    // Therefore references need to be manually deleted because otherwise the
    // references will first be cleaned if main() returns (application exit).
}
SDL_AndroidGetJNIEnv

CategoryAPI, CategorySystem, CategoryDraft


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