Why does maxWidth on a Button not work and how to

问题:

I have two buttons on the layout, and on a large-screen device (tablets) I want to cap their width so they don't look ridiculous. I expected to use the maxWidth attribute but it apparently does nothing in my scenario. Here's the layout definition - the buttons use up the full width of the layout, ignoring any value in maxWidth.

<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
>
<Button
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:maxWidth="100dp"
    android:text="Button 1"
/>
<Button
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:maxWidth="100dp"
    android:text="Button 2"
/>
</LinearLayout>

Why, and how to workaround this (apparently crazy) limitation?

回答1:

Remove the android:layout_weight="1" line from both buttons.
Add android:minWidth="50dp" and android:layout_width="wrap_content"

EDIT:

You need to calculate the button sizes manually depending on the screen size. First you need to have a standard screen size set. For example, If the you develop the app on a screen width 400px, and the button is 100px wide, then the formula for maintaining the same button width to screen width ratio on all devices will be as follows

 DisplayMetrics metrics = new DisplayMetrics();
 getWindowManager().getDefaultDisplay().getMetrics(metrics);
 buttonWidth = 100 * (metrics.widthPixels/400); 

Use case:
If screen width = 480px, then button width should be 120px.

回答2:

The good way of solving this is to create multiple layout for different combination of screen resolution. When you get at some max stretch, create a new layout that have fixed value where needed. See the section about "Use layout alias" in http://developer.android.com/training/multiscreen/screensizes.html#TaskUseAliasFilters

回答3:

Try setting the layout_width to wrap_content vs. 0dp.

回答4:

Width/Height seem to always ahve to be set together,.. This is working in my view

        <Button
            android:text="Center"
            android:layout_width="100dp"
            android:layout_height="fill_parent"
            android:id="@+id/selectionCenterButton"
            android:minWidth="50dp"
            android:minHeight="50dp"
            android:maxWidth="100dp"
            android:maxHeight="50dp"
            android:layout_weight="1" />

The button's parent is set to wrap content, so scales down, but up to a max of 400 wide (4 buttons)