Android: How to get a modal dialog or similar modal behavior?

Question

These days I\'m working on simulating modal dialog in Android. I\'ve googled a lot, there\'s much discussions but sadly there\'s not much options to get it modal. Here\'s so

Answer 1

Finally I ended up with a really straight and simple solution.

People who's familiar with Win32 programming possibly knows how to implement a modal dialog. Generally it runs a nested message loop (by GetMessage/PostMessage) when there is a modal dialog up. So, I tried to implement my own modal dialog in this traditional way.

At the first, android didn't provide interfaces to inject into ui thread message loop, or I didn't find one. When I looked into source, Looper.loop(), I found it's exactly what I wanted. But still, MessageQueue/Message haven't provided public interfaces. Fortunately, we have reflection in java. Basically, I just copied exactly what Looper.loop() did, it blocked workflow and still properly handled events. I haven't tested nested modal dialog, but theoretically it would work.

Here's my source code,

public class ModalDialog {

private boolean mChoice = false;        
private boolean mQuitModal = false;     

private Method mMsgQueueNextMethod = null;
private Field mMsgTargetFiled = null;

public ModalDialog() {
}

public void showAlertDialog(Context context, String info) {
    if (!prepareModal()) {
        return;
    }

    // build alert dialog
    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setMessage(info);
    builder.setCancelable(false);
    builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            ModalDialog.this.mQuitModal = true;
            dialog.dismiss();
        }
    });

    AlertDialog alert = builder.create();
    alert.show();

    // run in modal mode
    doModal();
}

public boolean showConfirmDialog(Context context, String info) {
    if (!prepareModal()) {
        return false;
    }

    // reset choice
    mChoice = false;

    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setMessage(info);
    builder.setCancelable(false);
    builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            ModalDialog.this.mQuitModal = true;
            ModalDialog.this.mChoice = true;
            dialog.dismiss();
        }
    });

    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            ModalDialog.this.mQuitModal = true;
            ModalDialog.this.mChoice = false;
            dialog.cancel();
        }
    });

    AlertDialog alert = builder.create();
    alert.show();

    doModal();
    return mChoice;
}

private boolean prepareModal() {
    Class clsMsgQueue = null;
    Class clsMessage = null;

    try {
        clsMsgQueue = Class.forName("android.os.MessageQueue");
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
        return false;
    }

    try {
        clsMessage = Class.forName("android.os.Message");
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
        return false;
    }

    try {
        mMsgQueueNextMethod = clsMsgQueue.getDeclaredMethod("next", new Class[]{});
    } catch (SecurityException e) {
        e.printStackTrace();
        return false;
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
        return false;
    }

    mMsgQueueNextMethod.setAccessible(true);

    try {
        mMsgTargetFiled = clsMessage.getDeclaredField("target");
    } catch (SecurityException e) {
        e.printStackTrace();
        return false;
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
        return false;
    }

    mMsgTargetFiled.setAccessible(true);
    return true;
}

private void doModal() {
    mQuitModal = false;

    // get message queue associated with main UI thread
    MessageQueue queue = Looper.myQueue();
    while (!mQuitModal) {
        // call queue.next(), might block
        Message msg = null;
        try {
            msg = (Message)mMsgQueueNextMethod.invoke(queue, new Object[]{});
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }

        if (null != msg) {
            Handler target = null;
            try {
                target = (Handler)mMsgTargetFiled.get(msg);
            } catch (IllegalArgumentException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }

            if (target == null) {
                // No target is a magic identifier for the quit message.
                mQuitModal = true;
            }

            target.dispatchMessage(msg);
            msg.recycle();
        }
    }
}
}

Hopefully this would help.