Problem

If you open a heavyweight window when the user touches a menu item, you can easily cause a null pointer exception to be thrown and the app to crash.

Theory

Based on the error message, we're hitting the NPE in our call to create a new intent on line 528 of TiUIWindow.java. Because TiActivity.class is not null, activity must be null. This is set on line 185 of the same file, and passed to the createIntent method. My theory is that there is an interim period between when the menu closes and the window regains focus during which proxy.getTiContext().getActivity() will return null, and cause the NPE.

Sample Code

Drop the following in an app.js:

// open a heavyweight window
var win = Titanium.UI.createWindow({ backgroundColor: '#fff', fullscreen: true });
win.add(Ti.UI.createLabel({ text: 'Press your hardware menu button!' }));
win.open();
var modal = Ti.UI.createWindow();

// keep a pointer to the current activity
var currentActivity = win.activity;

// and make an options menu
currentActivity.onCreateOptionsMenu = function(e) {

    // this menu item will effectively work off "proxy.getTiContext().getActivity()",
    // which can be null if the timing is just right when the menu closes and the modal opens
    e.menu.add({ title: 'Crashes Often' }).addEventListener('click', function() {
        // simulate some heavy activity to get the modal ready; having this busy
        // wait present is what makes this bug reproducible
        for (var i = new Date().getTime() + 1000; i > new Date().getTime();) {
        }
        modal.open({ modal: true });
        setTimeout(function() {
            modal.close();
        }, 50);
    });

    // but we explicitly set the activity in this one to our outer activity (the main activity)
    // so it will never be null
    var intent = Ti.Android.createIntent({
        url: 'loginModalWindow.js'
    });
    intent.putExtra('modal', true);
    e.menu.add({ title: 'Never Crashes' }).addEventListener("click", function() {
        // simulate some heavy activity; it won't make a difference
        for (var i = new Date().getTime() + 1000; i > new Date().getTime();) {
        }
        // start the activity; it will fire off without a problem
        currentActivity.startActivity(intent);
    });

};

now drop the following into your tiapp.xml:

    <android xmlns:android="http://schemas.android.com/apk/res/android">
        <activities>
            <activity url="loginModalWindow.js" android:theme="@android:style/Theme.Dialog" />
        </activities>
    </android>

and finally drop the following in loginModalWindow.js:

var win = Ti.UI.currentWindow;
win.modal = true;

setTimeout(function() {
    win.close();
}, 50)

This sample app has two menu items, named "Crashes Often" and "Never Crashes". They both launch modal windows that close themselves right away. The difference is the method they use. "Crashes Often" uses the Titanium way of opening a modal window. "Never Crashes" uses a more native Android way to open the modal, and is not reliant on Titanium automagically determining the current activity that should launch our modal activity. Note that you may need to try "Crashes Often" a couple of times before the app will freeze, crash, and you'll see the NPE in your logs.

Exception

E/TiUncaughtHandler(11317): (main) [1236,5053] Sending event: exception on thread: main msg:java.lang.NullPointerException; Titanium 1.7.0,2011/02/18 18:13,16c2c7
E/TiUncaughtHandler(11317): java.lang.NullPointerException
E/TiUncaughtHandler(11317):     at android.content.ComponentName.<init>(ComponentName.java:75)
E/TiUncaughtHandler(11317):     at android.content.Intent.<init>(Intent.java:2652)
E/TiUncaughtHandler(11317):     at ti.modules.titanium.ui.TiUIWindow.createIntent(TiUIWindow.java:528)
E/TiUncaughtHandler(11317):     at ti.modules.titanium.ui.TiUIWindow.createNewActivity(TiUIWindow.java:186)
E/TiUncaughtHandler(11317):     at ti.modules.titanium.ui.TiUIWindow.<init>(TiUIWindow.java:110)
E/TiUncaughtHandler(11317):     at ti.modules.titanium.ui.WindowProxy.handleOpen(WindowProxy.java:98)
E/TiUncaughtHandler(11317):     at org.appcelerator.titanium.proxy.TiWindowProxy.handleMessage(TiWindowProxy.java:67)
E/TiUncaughtHandler(11317):     at ti.modules.titanium.ui.WindowProxy.handleMessage(WindowProxy.java:85)
E/TiUncaughtHandler(11317):     at android.os.Handler.dispatchMessage(Handler.java:95)
E/TiUncaughtHandler(11317):     at android.os.Looper.loop(Looper.java:123)
E/TiUncaughtHandler(11317):     at android.app.ActivityThread.main(ActivityThread.java:4370)
E/TiUncaughtHandler(11317):     at java.lang.reflect.Method.invokeNative(Native Method)
E/TiUncaughtHandler(11317):     at java.lang.reflect.Method.invoke(Method.java:521)
E/TiUncaughtHandler(11317):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:862)
E/TiUncaughtHandler(11317):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
E/TiUncaughtHandler(11317):     at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(11317): Uncaught handler: thread main exiting due to uncaught exception

Tested On

Titanium SDK version: 1.7.0 (02/18/11 18:13 316c2c7)
BROKEN on Android EPIC 4G 2.1

Associated Helpdesk Ticket

http://developer.appcelerator.com/helpdesk/view/75121">http://developer.appcelerator.com/helpdesk/view/75121