实现具有动态绘制内容的 Android 小部件的正确方法是什么？

Question

For my first and most awesomest Android project, I want to create a home screen widget which displays one of those Arc Clocks that all the kids are raving about these days.

Based on the limitations of RemoteViews , it looks to me that the appropriate way to get it actually drawn on the screen is to use an ImageView in the actual layout, then when it is updating, create a ShapeDrawable or two and draw them onto a newly created Bitmap . Then, set that Bitmap as the source of the ImageView.

There is Something about that process that I'm just not grokking, though. The following is the code I tried to use to update the widget. I get nothing drawn on the screen at all. The ImageView has a placeholder image just set by its src property. When I don't run the code to update it to my drawing, the placeholder image stays in place. So, I know this code is doing something , just obviously not the right thing.

RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.widget);
Bitmap bitmap = Bitmap.createBitmap(100, 100, Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);

ShapeDrawable drawable = new ShapeDrawable(new ArcShape(0, 360));
drawable.getPaint().setColor(0xffff0000);
drawable.getPaint().setStrokeWidth(5.0f);
drawable.setIntrinsicWidth(100);
drawable.setIntrinsicHeight(100);
drawable.draw(canvas);

views.setImageViewBitmap(R.id.ImageView01, bitmap);     
appWidgetManager.updateAppWidget(appWidgetId, views);

I knew it couldn't be that easy. So, am I even heading in the right direction?

---

Update

Ok, maybe that was too much information. The question I'm really trying to ask is this:

If I want to draw shapes on a widget, should I use an ImageView and create a bitmap from my ShapeDrawable or is there more appropriate way to draw into a widget where it is constrained by RemoteViews?

Answer 1

There is actually a widget called AnalogClock in the SDK that is very similar to what you are trying to do.

It is implemented as a class that extends View and is annotated with @RemoteView . It registers receivers on Intent.ACTION_TIME_TICK and Intent.ACTION_TIME_CHANGED and draws itself by overriding the onDraw method. Check out the source . The standard AlarmClock application exposes this view as a widget that can be added to the home screen.

I think that is a good (if not the best) way to implement what you described and obviously works well.

Answer 2

This works great:

Paint p = new Paint(); 
p.setAntiAlias(true);
p.setStyle(Style.STROKE);
p.setStrokeWidth(8);
p.setColor(0xFFFF0000);

Bitmap bitmap = Bitmap.createBitmap(100, 100, Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.drawArc(new RectF(10, 10, 90, 90), 0, 270, false, p);

RemoteViews views = new RemoteViews(updateService.getPackageName(), R.layout.main);
views.setImageViewBitmap(R.id.canvas, bitmap);

ComponentName componentName = new ComponentName(updateService, DashboardAppWidgetProvider.class);
AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(updateService);
appWidgetManager.updateAppWidget(componentName, views);

I guess the problem with your original code was just the way of drawing the arc - that's why nothing showed up.

BTW: You can find a customizable "Arc Clock" with a very small memory footprint in the Market by searching for "arc clock"!

Answer 3

To create an custom component, I would extend View or any subclass of View and override the onDraw(Canvas canvas) method to do your drawing. On the the canvas object you can call methods such as drawLine(), drawArc(), drawPicture(), drawPoints(), drawText(), drawRect(), etc.....

Here's more details.

Here's the api for canvas.

I believe you can then add your custom view to a remote view for the purpose of making a widget.