资源是颜色还是可绘制的？

Question

I have create a little custom view that extends ImageView. My custom view provides a method showError(int) , where I can pass a resource id, which should be displayed as the image views content. It would be great if I could pass a simple color resource id or a drawable resource id.

My problem is: how do I determine if the passed resource id is a Drawable or a Color?

My current approach is something like this:

class MyImageView extends ImageView{

     public void showError(int resId){

        try{
            int color = getResources().getColor(resId);
            setImageDrawable(new ColorDrawable(color));
        }catch(NotFoundException e){
            // it was not a Color resource so it must be a drawable
            setImageDrawable(getResources().getDrawable(resId));
        }

     }
}

Is it safe to do that? My assumption is, that a resource id really unique. I mean not unique in R.drawable or R.color, but completely unique in R

So that there is no

R.drawable.foo_drawable = 1;
R.color.foo_color = 1;

Is it correct that the id 1 will be assigned only to one of this resources but not to both?

Answer 1

You probably want to look up a TypedValue from the resources, to allow you to determine whether the value is a Color or a Drawable . Something like this should work without needing to throw and catch an exception:

TypedValue value = new TypedValue();
getResources().getValue(resId, value, true); // will throw if resId doesn't exist

// Check whether the returned value is a color or a reference
if (value.type >= TypedValue.TYPE_FIRST_COLOR_INT && value.type <= TypedValue.TYPE_LAST_COLOR_INT) {
    // It's a color
    setImageDrawable(new ColorDrawable(value.data));
} else if (value.type == TypedValue.TYPE_REFERENCE) {
    // It's a reference, hopefully to a drawable
    setImageDrawable(getResources().getDrawable(resId));
}

Answer 2

First of all, everything you get from getResources are drawables. ColorDrawable is just a subclass of Drawable as are BitMapDrawable and many others ( http://developer.android.com/guide/topics/resources/drawable-resource.html ).

Furthermore Android makes sure all values in the R file are unique (so it is impossible to get the same values like you described, even when they would of different instances). The only case it would return identical values is when the resource has not been found (it will return 0). Find the part about unique ID here

Hope this helps

Answer 3

Take a look inside your R.java file. You'll see that all the resource ids are defined in there, each one having a unique 32 bit number. They are also grouped together by type. For example you should see all your drawable ids in a group:

public static final class drawable {
    public static final int my_drawable_1=0x7f020000;
    public static final int my_drawable_2=0x7f020001;

The resource id is of the form PPTTNNNN where PP is always 0x7f and TT is the type. I expect all your drawables use '02' for the type, but worth checking your own file. In that case, if the id is between 0x7f020000 and 0x7f029999, you can assume it is a drawable.

Answer 4

You can do in this way too

 TypedValue value = new TypedValue();

 context.getResources().getValue(resId, value, true);

// Check if it is a reference
if (value.type == TypedValue.TYPE_REFERENCE) {
    ....
 }