How to have a Fullscreen Background Image (with center-crop) that doesn't Resize

Question

I'm trying to set a photo as the background of an Activity . I want the background to be a full screen image (no borders) .

As I want the image to fill the entire activity's background without stretching/squeezing (ie unproportional scalings for X and Y) and I don't mind if the photo has to be cropped, I'm using a RelativeLayout with an ImageView (with android:scaleType="centerCrop" ) and the rest of my layout consisting of a ScrollView and its children.

<!-- Tried this with a FrameLayout as well... -->
<RelativeLayout> 
   <!-- Background -->
   <ImageView  
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:scaleType="centerCrop"/>
   <!-- Form -->
   <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="match_parent">
      <ScrollView>
        <LinearLayout>
          ...
          <EditText/>
        </LinearLayout>
      </ScrollView>
   </LinearLayout>
</RelativeLayout>

The problem is that the rest of the layout has some EditText views and when the softkeyboard shows up, the ImageView gets re-sized. I would like the background to remain the same, irregardless of whether the softkeyboard is visible or not.

I have seen plenty of questions on SO about ImageViews being re-sized but (imo) no satisfactory answers. Most of them just consist of setting the android:windowSoftInputMode="adjustPan" - which is not always practical, especially if you want the user to be able to scroll in the activity - or using getWindow().setBackgroundDrawable() which doesn't crop the image.

I've managed to sub-class ImageView and override its onMeasure() (see my answer here: ImageView resizes when keyboard open ) so that it can force a fixed height & width - equal to the device's screen dimensions - according to a flag but I'm wondering if there's a better way of achieving the result I want.

So, to sum up, my question is: How can I set an Activity's background to be a full-screen photo

• with scale type = "centerCrop", so that the photo is scaled uniformly (maintaining its aspect ratio) and therefore both dimensions (width and height) of will be equal to or larger than the corresponding dimension of the view;

• that doesn't get resized when a softkeyboard pops up;

---

ANSWER:

I ended up following @pskink 's advice and subclassed BitmapDrawable (see his answer bellow). I had to do some adjustments to make sure that the BackgroundBitmapDrawable is always scaled and cropped in a way that fills the screen.

Here's my final class, adapted from his answer:

public class BackgroundBitmapDrawable extends BitmapDrawable {
    private Matrix mMatrix = new Matrix();
    private int moldHeight;
    boolean simpleMapping = false;

    public BackgroundBitmapDrawable(Resources res, Bitmap bitmap) {
        super(res, bitmap);
    }

    @Override
    protected void onBoundsChange(Rect bounds) {
        if (bounds.height() > moldHeight) {
            moldHeight = bounds.height();
            Bitmap b = getBitmap();
            RectF src = new RectF(0, 0, b.getWidth(), b.getHeight());
            RectF dst;

            if (simpleMapping) {
                dst = new RectF(bounds);
                mMatrix.setRectToRect(src, dst, ScaleToFit.CENTER);
            } else {
                // Full Screen Image -> Always scale and center-crop in order to fill the screen
                float dwidth = src.width();
                float dheight = src.height();

                float vwidth = bounds.width(); 
                float vheight = bounds.height();

                float scale;
                float dx = 0, dy = 0;

                if (dwidth * vheight > vwidth * dheight) {
                    scale = (float) vheight / (float) dheight; 
                    dx = (vwidth - dwidth * scale) * 0.5f;
                } else {
                    scale = (float) vwidth / (float) dwidth;
                    dy = (vheight - dheight * scale) * 0.5f;
                }

                mMatrix.setScale(scale, scale);
                mMatrix.postTranslate(dx, dy);

            }
        }
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawColor(0xaa00ff00);
        canvas.drawBitmap(getBitmap(), mMatrix, null);
    }
}

Then its just a matter of creating a BackgroundBitmapDrawable and setting it as the root View's background.

Answer 1

try this LayerDrawable (res/drawable/backlayer.xml):

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android"
>
    <item>
        <shape>
        <solid android:color="#f00" />
        </shape>
    </item>
<item>
        <bitmap
        android:gravity="top" android:src="@drawable/back1">
        </bitmap>
    </item>
</layer-list>

and set it to your top level layout: android:background="@drawable/backlayer"

UPDATE: try this BitmapDrawadle, set it to top level layout (setBackgroundDrawable()), if simpleMapping == true is good enough you can remove "else" branch:

class D extends BitmapDrawable {
    private Matrix mMatrix = new Matrix();
    private int moldHeight;

    public D(Resources res, Bitmap bitmap) {
        super(res, bitmap);
    }

    @Override
    protected void onBoundsChange(Rect bounds) {
        if (bounds.height() > moldHeight) {
            moldHeight = bounds.height();
            Bitmap b = getBitmap();
            RectF src = new RectF(0, 0, b.getWidth(), b.getHeight());
            RectF dst;

            // if simpleMapping is good enough then remove "else" branch and
            // declare "dst" as:
            // RectF dst = new RectF(bounds);
            boolean simpleMapping = true;
            if (simpleMapping) {
                dst = new RectF(bounds);
            } else {
                float x = bounds.exactCenterX();
                dst = new RectF(x, 0, x, bounds.height());
                float scale = bounds.height() / src.height();
                float dx = scale * src.width() / 2;
                dst.inset(-dx, 0);
            }
            mMatrix.setRectToRect(src, dst, ScaleToFit.CENTER);
        }
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawColor(0xaa00ff00);
        canvas.drawBitmap(getBitmap(), mMatrix, null);
    }
}

Answer 2

将所有内容放在FrameLayout中，第一个子图像将与其父图像（frameLayout）相匹配，并将其配置为您想要的背景，并在图像视图前放置您想要的任何内容（我猜想是LinearLayout）

Answer 3

After scratching my head for a while this has been my "good for now" solution.

Sharing a sample XML that might be useful for anyone.

<!-- RelativeLayout so that Views can overlap each other.
     I believe a FrameLayout would work as well. -->
<RelativeLayout
    android:id="@+id/root"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <!-- I've put the ImageView inside 
         a ScrollView with android:fillViewport="true" and android:isScrollContainer="false" -->
    <ScrollView
        android:id="@+id/backgroundScrollView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fillViewport="true"
        android:isScrollContainer="false" > 

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical" >

            <!-- The FullScreen, Center-Cropped Image Background --> 
            <ImageView
                android:id="@+id/backgroundImage"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:scaleType="centerCrop"
                android:src="@drawable/background_image" />
        </LinearLayout>
    </ScrollView>

    <!-- The rest of the Views, containing the data entry form... -->
    <LinearLayout
        android:id="@+id/form"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical" >

            <ScrollView
                android:id="@+id/formScrollView"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" >

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:layout_weight="1"
                    android:orientation="vertical" >

                    <!-- The "Form", with EditTexts, Checkboxes and whatnot... -->

                </LinearLayout>
            </ScrollView>

    </LinearLayout>
</RelativeLayout>

With this layout, I accomplish two things:

• formScrollView , which contains the "form" with the EditTexts, etc. gets re-sized (as I want it to) and scrollable when the softkeyboard shows up.

• backgroundScrollView , which contains the ImageView, doesn't get re-sized (because of the android:isScrollContainer="false" ) and fills the entire viewport ( android:fillViewport="true" ). Thus the background remains the same irregardless of whether the keyboard is visible or not.

Not a perfect solution as the ImageView somehow suffers a very small variation in its size, but the result is good enough for now. If someone knows a better solution, please let me know.

Answer 4

The solution in the answer is the best, to use it:

Resources res = getActivity().getResources();
Bitmap bitmap = BitmapFactory.decodeResource(res, R.drawable.some_image);
BackgroundBitmapDrawable background = new BackgroundBitmapDrawable(res, bitmap);
view.setBackgroundDrawable(background);

or

view.setBackground(background);

for API 16 and above.

Answer 5

Change your ScaleType

 android:scaleType="FitXY"

and in your manifest

<activity
           android:name=".activity.MainActivity"
            android:windowSoftInputMode="adjustPan|stateHidden" />

Answer 6

Create an ImageView in your xml. Place it below your Layout tag. Set the translationZ to a positive value say 10dp and the scaleType to centerCrop.