How to store drawable in an array

问题

I want to download a bunch of images and would like to store it as drawable in an array. So I tried declaring a drawable array.But it returns me nullPointer exception when I access that array.

My question is, how to declare an array type as drawable ?

回答1:

an array of drawables would be declared like:

int numDrawables = 10;
Drawable[] drawableArray = new Drawable[numDrawables];

to fill the array:

for(int i = 0; i < numDrawables; i++){
    // get a drawable from somewhere
    Drawable drawable = new Drawable();
    drawableArray[i] = drawable;
}

to access the array:

Drawable aDrawable = drawableArray[0];

This is basic java, If you are getting null pointer exceptions, you are doing something wrong.

回答2:

you can use an hashMap , and put the keys as urls for example , and to value is the drawable that you download :

HashMap<String,Drawable> myDrawables = new HashMap<String,Drawable>();
//before you download the images, you can test if your drawable is already downloaded, 
// with looking for his url in the Hashmap , 
.....
myDrawables.put(urlOfYourDrawable, yourDrawable);

回答3:

If you want to store list of elements(any type) dynamically use the classes in the collection. why because Array size is static. Example:

ArrayList<Generic> list=new ArrayList<Generic>();

list.add(Generic);

来源：https://stackoverflow.com/questions/6213444/how-to-store-drawable-in-an-array