Warning: This <FrameLayout> can be replaced with a <merge> tag

问题

I have a FrameLayout that contains a TextView and two LinearLayouts:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >


    ... a textview and 2 linearlayouts


</FrameLayout>

After running Android Lint, I get this warning: This <FrameLayout> can be replaced with a <merge> tag.

Why does this warning exist? What can I do to fix it (other than ignore)?

回答1:

To understand this, you need to understand how layout are inflated and placed.

Let's say for example, you have a activity and this is the layout xml you use. Here is what the layout of the activity looks before you put your layout file.

<FrameLayout // This is the window
    ...
    <FrameLayout> // This is activity
    </FrameLayout>
</FrameLayout>

There might be a few other layers depending on the device/OS.

Now when you inflate your layout file and put it in, this is how it will look.

<FrameLayout // This is the window
    ...
    <FrameLayout> // This is activity
        // Your layout below
        <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent" >
                ... a textview and 2 linearlayouts
        </FrameLayout>
    </FrameLayout>
</FrameLayout>

Do you see the FrameLayout inside a FrameLayout? It is redundant to have that since it does not add much value. To optimize, you can replace your FrameLayout with a < merge >. If you use , this is what it will look like.

<FrameLayout // This is the window
    ...
    <FrameLayout // This is activity
        // Your layout below
                ... a textview and 2 linearlayouts
    </FrameLayout>
</FrameLayout>

Notice how there is no extra FrameLayout. Instead, it is just merged with the FrameLayout of the activity. Whenever you can, you should use < merge >. This doesn't only apply to FrameLayouts. You can read more about it here. http://developer.android.com/training/improving-layouts/reusing-layouts.html#Merge

Hope this helps.

回答2:

Are you using this as the main layout of your activity? If so, you can replace it with a merge tag like this:

<merge xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    ... a textview and 2 linearlayouts


</merge>

At setContentView, Android will take the children of the merge tag and directly insert them to the FrameLayout with @android:id/content. Examine both approaches (FrameLayout vs merge) with HierarachyViewer to see the difference.

回答3:

Refer this post by the Romain Guy for more information. It tells you why the merge option is suggested.

来源：https://stackoverflow.com/questions/21488027/warning-this-framelayout-can-be-replaced-with-a-merge-tag