Android: why should IDs of views should be positive numbers?

问题:

In View.java,

setId - "Sets the identifier for this view. The identifier does not have to be unique in this view's hierarchy. The identifier should be a positive number."

&

findViewById - "Look for a child view with the given id. If this view has the given id,

Why I could not use a negative number as the id of the view? I commented out the

    public final View findViewById(int id) {     // The original android check at here     //  if (id < 0) {      // is commented out to test if system could run when Ids are negative numbers     if (id == NO_ID) {         return null;     }     return findViewTraversal(id); }

The system seems to be working fine.

回答1:

It most likely is just a design decision. Negative identifiers are commonly used to notify that there's something wrong with the underlying entity, thus using negative id's is often frowned upon.

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