Every time I work on the UI of Android app I get the feeling that there is either something terribly wrong with the Android UI framework or with my understanding of how it works. I can reason about how the app works on the higher level, but I cannot apply the same methodology to Android UI, except for the simplest designs. I have read a lot of Android source code, I have written few dozens of sample-like apps, but I still cannot just think of the views structure, type it in and be done - for complicated layouts with some optional elements (i.e. which are sometimes visible and sometimes gone) I need at least few attempts and, I confess, sometimes I'm desperate enough to do the "let's change this and see what happens" coding. Extremely frustrating.
I'm going to describe my struggles with Android UI on this blog, so if I'm doing something terribly wrong, hopefully someone will enlighten me by posting a comment; and in case something is terribly wrong with Android UI framework, I might be able to help other programmers in distress.
Today I have a simple task for you: create a button with some text and icon to the left of the text. The contents (both icon and text) should be centered inside the button.
That's simple right? Here's the XML layout which comes to mind first:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:drawableLeft="@android:drawable/ic_delete"
android:gravity="center"
android:text="Button Challenge" />
</LinearLayout>
Unfortunately, no cookie for you:
Someone decided that compound drawables should be always draw next to the View's padding, so we have to try something else. For example TextView centered inside the FrameLayout.
<FrameLayout
style="?android:attr/buttonStyle"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:drawableLeft="@android:drawable/ic_delete"
android:gravity="center"
android:text="Button Challenge" />
</FrameLayout>
Almost there, but the text has a wrong size and color. There is something called "textAppearanceButton", but apparently it's not what the Buttons use:
OK, so let's use the buttonStyle again, this time on TextView:
Now we need to get rid of the extra background, reset minimum height and width and make it not focusable and not clickable (otherwise tapping the caption won't have any effect):
<FrameLayout
style="?android:attr/buttonStyle"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<TextView
style="?android:attr/buttonStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:background="@null"
android:clickable="false"
android:drawableLeft="@android:drawable/ic_delete"
android:focusable="false"
android:gravity="center"
android:minHeight="0dp"
android:minWidth="0dp"
android:text="Button Challenge" />
</FrameLayout>
Lo and behold, it works!
We'd really like to use is something like textAppearance="?android:attr/buttonStyle.textAppearance", but there is no such syntax. How about extracting all the attributes from TextView into some "buttonCaption" style with "?android:attr/buttonStyle" parent? No can do either: you can only inherit your style from the concrete @style, not from the styleable attribute.
But what we can do is to use Button and create a style with no parent: Android will use the default button style and apply our captionOnly style:
<style name="captionOnly">
<item name="android:background">@null</item>
<item name="android:clickable">false</item>
<item name="android:focusable">false</item>
<item name="android:minHeight">0dp</item>
<item name="android:minWidth">0dp</item>
</style>
<FrameLayout
style="?android:attr/buttonStyle"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<Button
style="@style/captionOnly"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:drawableLeft="@android:drawable/ic_delete"
android:gravity="center"
android:text="Button Challenge" />
</FrameLayout>
