(can't find id reference) No resource matches

问题:

I have the following inside a relative layout.

<TextEdit
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@id/buttonA"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:layout_toLeftOf="@id/buttonA" />

<Button
    android:id="@+id/buttonA"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:text="@string/message" >
</Button>

Eclipse gives me these errors at lines android:layout_alignBottom="@id/buttonA" and android:layout_toLeftOf="@id/buttonA" respectively:

error: Error: No resource found that matches the given name (at 'layout_alignBottom' with value '@id/buttonA').

error: Error: No resource found that matches the given name (at 'layout_toLeftOf' with value '@id/buttonA').

Replacing @id/buttonA with @+id/buttonA removes this eclipse error message. Is that the right thing to do? If so, why would that work instead? Doesn't @+id create a new id? I don't want a new id. I want to use the one referenced in the button object. What is the best way to deal with this?

Thanks guys. -Joe

回答1:

Using @+id is the right way to do it. @+id creates a new id but only if one with that name doesn't already exist.

If you don't want to do that, for this particular simple case it would suffice to move the TextEdit below the Button.

回答2:

The layout which you are trying to use as reference should be defined before it is used as reference i.e. use as 'layout_toLeftOf'.

It is like you have to declare a variable in java before using it. Declare then use it ...