通过 NDK 回调在 Android 中创建消息对话框

Question

我有一个 android 应用程序，在其中我在 Java 端设置了 OpenGL 上下文，并从 NDK/C++ 端发送绘图。这一切似乎都运作良好。

我希望 C++ 端能够弹出一个对话框。我实现了一个 java MakeADialog 函数，它可以通过 env->CallVoidMethod(javaClass, javaMethod); 从 C 端很好地触发我的 Java 端接收函数如下所示：

public static void MakeADialog() {  
     Log.w("title", "MakeADialog fired!");
}

这是一个单独的类（不是Activity 或Runnable）。以上工作正常，我可以看到我的 MakeADialg 日志消息。但是，当我尝试创建一个实际的对话框时，我会遇到很多崩溃。当我从 C 端调用到 Java 端时，我可以说我并没有在运行什么“线程”。当我尝试创建新线程/对话框时，我似乎遇到了麻烦。

我在这里尝试了很多关于创建 Runnable、线程等的建议 - 但它们似乎总是给我可怕的“无法在未调用 Looper.prepare() 的线程内创建处理程序”或该视图的父级为空。这些方法中的大多数都围绕将 Activity 和 Context 指针存储为静态并在我处于 MakeADialog 回调时通过 get 函数检索它们。

AlertDialog alertDialog = new AlertDialog.Builder(MyApp.GetMyContext()).create(); 其中 GetMyContext() 函数仅返回我在应用启动期间存储的主 Activity 创建线程的 this 指针。

有没有人弹出从他们的 NDK 端启动的对话框，或者可以向我指出一些相关文档，以帮助我了解如何从 NDK 回调创建新对话框？

提前致谢！

Answer 1

也许我们可以使用gist 中的示例来创建模态对话框。我怀疑你是从工作线程中调用它的，所以“他们似乎总是给我可怕的‘无法在未调用 Looper.prepare() 的线程内创建处理程序’，或者视图的父级为空。” （另见Can't create handler inside thread that has not called Looper.prepare()）。

基于官方示例Native Activity和the gist code的键码：

1. 在 Java 方面，

package ss.fang.brickgo;

import android.app.AlertDialog;
import android.app.Dialog;
import android.app.NativeActivity;
import android.content.DialogInterface;
import android.content.pm.ApplicationInfo;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.os.Looper;
import android.util.Log;
import android.view.Window;
import android.view.WindowManager;

import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicInteger;

public class GameActivity extends NativeActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    /**
     * This function will be called from C++ by name and signature (Ljava/lang/String;Z)I)
     *
     * @param message the message text to show
     * @param model   if true, it will block the current thread, otherwise, it acts like a modeless dialog.
     * @return return id of the button that was clicked for a model dialog, otherwise, 0.
     * @see #showAlertCallback
     * @see <a href="https://*.com/questions/11730001/create-a-message-dialog-in-android-via-ndk-callback/60611870#60611870">
     * Create a message dialog in Android via NDK callback</a>
     * @see <a href="https://*.com/questions/6120567/android-how-to-get-a-modal-dialog-or-similar-modal-behavior">
     * Android: How to get a modal dialog or similar modal behavior?</a>
     */
    public int showAlert(final String message, boolean model) {
        //https://*.com/questions/11411022/how-to-check-if-current-thread-is-not-main-thread
        if (Looper.myLooper() == Looper.getMainLooper() && model) {
            // Current Thread is UI Thread. Looper.getMainLooper().isCurrentThread()
            //android.os.NetworkOnMainThreadException
            throw new RuntimeException("Can't create a model dialog inside Main thread");
        }
        ApplicationInfo applicationInfo = getApplicationInfo();
        final CharSequence appName = getPackageManager().getApplicationLabel(applicationInfo);
        // Use a semaphore to create a modal dialog. Also, it's holden by the dialog's listener.
        final Semaphore semaphore = model ? new Semaphore(0, true) : null;
        // The button that was clicked (ex. BUTTON_POSITIVE) or the position of the item clicked
        final AtomicInteger buttonId = new AtomicInteger();
        this.runOnUiThread(new Runnable() {
            public void run() {
                AlertDialog.Builder builder = new AlertDialog.Builder(GameActivity.this, AlertDialog.THEME_HOLO_DARK);
                builder.setTitle(appName);
                builder.setMessage(message);
                DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        buttonId.set(id);
                        if (null != semaphore)
                            semaphore.release();
                        else
                            showAlertCallback(id);
                        if (DialogInterface.BUTTON_POSITIVE == id) {
                            GameActivity.this.finish();
                        }
                    }
                };
                builder.setNegativeButton(android.R.string.cancel, listener);
                builder.setPositiveButton(android.R.string.ok, listener);
                builder.setCancelable(false);
                AlertDialog dialog = builder.create();
                dialog.show();
            }
        });
        if (null != semaphore)
            try {
                semaphore.acquire();
            } catch (InterruptedException e) {
                Log.v("GameActivity", "ignored", e);
            }
        return buttonId.get();
    }

    /**
     * The callback for showAlert when it acts like a modeless dialog
     *
     * @param id the button that was clicked
     */
    public native void showAlertCallback(int id);

    /**
     * @see <a href="https://*.com/questions/13822842/dialogfragment-with-clear-background-not-dimmed">
     * DialogFragment with clear background (not dimmed)</a>
     */
    protected void showDialog() {
        Dialog dialog = new Dialog(this);
        dialog.getWindow().requestFeature(Window.FEATURE_NO_TITLE);
        dialog.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        // layout to display
        dialog.setContentView(R.layout.dialog_layout);

        // set color transpartent
        dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

        dialog.show();
    }
}

1. 在本机 (C++11) 方面，

/** @param onClickListener MUST be NULL because the model dialog is not implemented. */
typedef void *(OnClickListener)(int id);

jint showAlert(struct android_app *state, const char *message, bool model = false);

/** Process the next input event. */
static int32_t engine_handle_input(struct android_app *app, AInputEvent *event) {
    auto *engine = (struct engine *) app->userData;
    auto type = AInputEvent_getType(event);
    if (AINPUT_EVENT_TYPE_MOTION == type) {
        engine->animating = 1;
        engine->state.x = AMotionEvent_getX(event, 0);
        engine->state.y = AMotionEvent_getY(event, 0);
        return 1;
    } else if (AINPUT_EVENT_TYPE_KEY == type) {
        auto action = AKeyEvent_getAction(event);
        if (AKEY_EVENT_ACTION_DOWN == action && AKEYCODE_BACK == AKeyEvent_getKeyCode(event)) {
            //https://*.com/questions/15913080/crash-when-closing-soft-keyboard-while-using-native-activity
            // skip predispatch (all it does is send to the IME)
            //if (!AInputQueue_preDispatchEvent(app->inputQueue, event))
            //int32_t handled = 0;
            //if (app->onInputEvent != NULL) handled = app->onInputEvent(app, event);
            //AInputQueue_finishEvent(app->inputQueue, event, handled);
            LOGI("Before showAlert in modal behavior, it blocks until the dialog dismisses.");
            showAlert(app, "Go Back?", true);
            LOGI("After showAlert in modal behavior, the dialog should have been dismissed.");
            return 1;
        }
    }
    return 0; //not handled
}

/** @return the id of the button clicked if model is true, or 0 */
jint showAlert(struct android_app *state, const char *message, bool model /* = false */) {
    JNIEnv *jni = NULL;
    state->activity->vm->AttachCurrentThread(&jni, NULL);

    jclass clazz = jni->GetObjectClass(state->activity->clazz);

    // Get the ID of the method we want to call
    // This must match the name and signature from the Java side Signature has to match java
    // implementation (second string hints a java string parameter)
    jmethodID methodID = jni->GetMethodID(clazz, "showAlert", "(Ljava/lang/String;Z)I");

    // Strings passed to the function need to be converted to a java string object
    jstring jmessage = jni->NewStringUTF(message);

    jint result = jni->CallIntMethod(state->activity->clazz, methodID, jmessage, model);

    // Remember to clean up passed values
    jni->DeleteLocalRef(jmessage);

    state->activity->vm->DetachCurrentThread();

    return result;
}

extern "C"
JNIEXPORT void JNICALL
Java_ss_fang_brickgo_GameActivity_showAlertCallback(JNIEnv *env, jobject thiz, jint id) {
    LOGI("showAlertCallback %d", id);
}