Android Toast FAQ: How do I create a Toast message in Android? (Or, Can you share some Android Toast message syntax examples?)
Here's one example of the Android Toast syntax:
Toast.makeText(ProjectActivity.this, "Your message here" , Toast.LENGTH_SHORT).show();
and here's a second example, this time referring to the Android application context as the first method parameter:
Android FAQ: What is Android doing when it says “optimizing apps” after an Android system upgrade (and reboot)?
The short story is that Android is doing what it says, creating an optimized version of each app for the new version of Android you just upgraded to. This process makes each app start as fast as possible with the new Android version.
My main project right now (through Valley Programming of Broomfield, Colorado) is porting my Back To Now mindfulness reminder app (formerly named Just Be) to run on both Android and iOS. It’s great to have a toolkit where I can write an app for Android and iOS using one set of code.
As an Android developer, you can normally use the adb push command to copy files from your computer’s hard drive to an Android device. However, I just ran into a problem where I couldn’t copy files to my Android emulator’s “data” directory, i.e., the /data/data filesystem. When I tried to copy a file using this command:
$ adb push foo.jpg /data/data/com.alvinalexander.myapp/files
I got this Android error:
If you’re working with an Android application, this source code seems to work to load an image from a file:
Bitmap bitmap = BitmapFactory.decodeFile(pathToPicture);
The Bitmap and BitmapFactory classes are located in the android.graphics package:
import android.graphics.Bitmap; import android.graphics.BitmapFactory;
Assuming that your pathToPicture is correct, you can then add this bitmap image to an ImageView like this:
Before I completely delete this code from my current Android application, I want to make a copy of it here. It was intended to show a series of quotes (text phrases) in a “Grid” (GridView), but (a) I never got it working as desired, and (b) I decided I didn’t want it in my application anyway.
Here’s the source code for the Java controller/fragment class:
XO Play is a “thinking man’s” football game that I created for Android devices. It’s for those of us who enjoy thinking about football strategy, of how to take advantage of our strengths and our opponents’ weaknesses, and how to call plays to win games. If you’ve ever watched a football game and thought, “I can call plays better than this guy,” XO Play is for you.
Version 1.4 introduces four game levels you can choose from:
The UI still needs a lot of work, but I like the idea of having an Inconceivable mode in the next version of my XO Play Android football game.
I’m working on a very small Android “notifications” app where I a) display a notification using a background service, b) the user taps the notification, which c) takes them to a view that shows the full text of the notification. To get this to work, I need to send the full text along with the notification. However, this didn’t work easily. The text that was shown by my full view would be updated once, then never again.
After a lot of googling and trial and error, I finally got this approach in my sendNotification method working:
I need a new tablet, and I just might bite the bullet on the Amazon Fire 10 HD today (Black Friday, 2018). For my Android development I don’t like that it’s based on Android 5, but $100 (33% off its regular price) for a tablet with decent performance is hard to pass up for my current needs.
I was just working on centering some components in an Android LinearLayout and came upon this helpful advice:
android:gravity takes care of its children,
android:layout_gravity takes care of itself
So, in my case, where I wanted to center two buttons horizontally in a LinearLayout, I used android:gravity="center".
Android Button FAQ: How do I add a listener to a Button in Android?
To add a click (tap) listener to a button in Android, just get a reference to the button (typically using findViewById), then call the setOnClickListener method of the button, like this:
Android FAQ: How do I programmatically set the font size (and/or font style) for an Android TextView?
Solution: Setting the Android TextView font size programmatically is a simple two-step process. First, define everything about the font that you want to use in a resources file. For example, I put this code in a file named res/values/styles.xml:
I just started working with the Android Room database persistence library, and since you’re not supposed to run things like database queries on the main thread (the UI thread), I was looking at other ways to run them.
In general, you probably won’t want to run database queries using a Thread, but just to see how Room works, I wrote this Java Thread code, and confirmed that it works as expected:
// works (pre-java8)
Thread t = new Thread() {
public void run() {
mAppDatabase.userDao().insert(u);
}
};
t.start();
Since that code runs in a separate thread, it runs fine even if I enable Android’s StrictMode.
Then I thought, “Hey, if I use the Android Studio 3 Canary Preview, I can use Android’s Java 8 features,” and when I did that I was able to use this Java 8 Thread syntax for the same purpose:
// works (java8)
new Thread(() -> {
mAppDatabase.userDao().insert(u);
}).start();
That also works, and it’s much easier to read than the old Java Thread syntax.
As a quick summary, if you want to use a Java 8 Thread with Android, I hope that last example is helpful. I don’t often interact with a database without calling back to update the UI, but when I’m writing a little test app, or testing new features like the Android Room persistence library, this is a simple approach to keep database I/O code off the main thread.
As another quick Android example, this Java source code shows how to add a “click listener” (on click/tap event) to an Android Button:
Android error FAQ: Help, I'm developing an Android app, and I'm getting a "Unfortunately your Android app has stopped error message"; how do I fix it?
If you're getting an Android error message that looks like this:
"Unfortunately your Android app has stopped error message"
It's probably because you forgot to put a new Activity in the AndroidManifest.xml file (or at least that's been the #1 cause of this error message in my experience).
I’m not an expert on this subject just yet, but if you want the source code for an Android method to center text that you want to use with the drawText method of the Canvas class, I know that this code works in two places in my current Android app:
The following Java source code shows how to determine the screen size (dimensions) of the Android device your application is running on:
Android FAQ: How do I write a custom View class in Android? (Or, how do I extend a View class?)
As a quick note today, here’s a little Java method that I use to log Android memory use (RAM use) from an Activity or Fragment:
private void logMemoryInfo(Context context, String TAG) {
ActivityManager activityManager = (ActivityManager) context.getSystemService(getActivity().ACTIVITY_SERVICE);
int memoryClass = activityManager.getMemoryClass();
ActivityManager.MemoryInfo memoryInfo = new ActivityManager.MemoryInfo();
activityManager.getMemoryInfo(memoryInfo);
Log.i(TAG, "\n------------ RAM -------------");
Log.i(TAG, "mem class: " + memoryClass);
Log.i(TAG, "mem avail: " + memoryInfo.availMem);
Log.i(TAG, "low mem: " + memoryInfo.lowMemory);
Log.i(TAG, "threshold: " + memoryInfo.threshold);
long mb = 1024*1024;
Runtime runtime = Runtime.getRuntime();
Log.i(TAG, "Used Memory: " + (runtime.totalMemory() - runtime.freeMemory()) / mb);
Log.i(TAG, "Free Memory: " + runtime.freeMemory() / mb);
Log.i(TAG, "Total Memory: " + runtime.totalMemory() / mb);
Log.i(TAG, "Max Memory: " + runtime.maxMemory() / mb);
}