Scale image keeping its aspect ratio in background

问题:

How do I make a background image fit the view but keep its aspect ratio when using <bitmap /> as a background drawable XML? None of <bitmap>'s android:gravity values gives the desired effect.

回答1:

It is impossible to achieve manipulating background attribute within xml-files only. There are two options:

1. You cut/scale the bitmap programmatically with Bitmap.createScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter) and set it as some View's background.

2. You use ImageView instead of background placing it as the first layout's element and specify android:scaleType attribute for it:

   <RelativeLayout
       android:layout_width="fill_parent"
       android:layout_height="fill_parent" >
   
       <ImageView
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
   
           android:src="@drawable/backgrnd"
           android:scaleType="centerCrop" />
   
       ...
   
       rest layout components here
   
       ...
   
   </RelativeLayout>
   

回答2:

There is an easy way to do this from the drawable:

your_drawable.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >

    <item android:drawable="@color/bg_color"/>
    <item>
        <bitmap
            android:gravity="center|bottom|clip_vertical"
            android:src="@drawable/your_image" />
    </item>

</layer-list>

The only downside is that if there is not enough space, your image won't be fully shown, but it will be clipped, I couldn't find an way to do this directly from a drawable. But from the tests I did it works pretty well, and it doesn't clip that much of the image. You could play more with the gravity options.

Another way will be to just create an layout, where you will use an ImageView and set the scaleType to fitCenter.

Hope this information helps you achieve what you want.

回答3:

Another approach would be to create patch 9 images of your regular image and have it stretch scale the way you want it to.

You could have it center the content by putting 9-patch-dots in the corners that will preserve your ratio obviously (assuming the outer most edge of your image is repeatable/transparent).

Hopefully you get the idea.

回答4:

I wanted to do something similar in my custom Drawable class. Here are the important pieces:

public class CustomBackgroundDrawable extends Drawable
{
    private Rect mTempRect = new Rect();
    private Paint mBitmapPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    ...

public void draw(@NonNull Canvas canvas)
{
    Rect bounds = getBounds();
    if (mBitmap != null ) {
        if (mScaleType == ScaleType.SCALE_FILL) {
            //bitmap scales to fill the whole bounds area (bitmap can be cropped)
            if (bounds.height() > 0 && bounds.height() > 0) {
                float scale = Math.min(mBitmap.getWidth()/(float)bounds.width(), mBitmap.getHeight()/(float)bounds.height());

                float bitmapVisibleWidth = scale * bounds.width();
                float bitmapVisibleHeight = scale * bounds.height();

                mTempRect.set((int)(mBitmap.getWidth()-bitmapVisibleWidth)/2, 0, (int)(bitmapVisibleWidth+mBitmap.getWidth())/2, (int)bitmapVisibleHeight);
                canvas.drawBitmap(mBitmap, mTempRect, bounds, mBitmapPaint);
            }
        } else if (mScaleType == ScaleType.SCALE_FIT) {
            //bitmap scales to fit in bounds area
            if (bounds.height() > 0 && bounds.height() > 0) {
                float scale = Math.min((float)bounds.width()/mBitmap.getWidth(), (float)bounds.height()/mBitmap.getHeight());

                float bitmapScaledWidth = scale * mBitmap.getWidth();
                float bitmapScaledHeight = scale * mBitmap.getHeight();
                int centerPadding = (int)(bounds.width()-bitmapScaledWidth)/2;
                mTempRect.set(bounds.left + centerPadding, bounds.top, bounds.right - centerPadding, bounds.top+(int)bitmapScaledHeight);
                canvas.drawBitmap(mBitmap, null, mTempRect, mBitmapPaint);
            }
        }
    }
}

With this approach you are flexible to apply any scale logic that you need

回答5:

Using the method described by a.ch worked great for me except I used this scale type which worked much better for what I needed:

android:scaleType="centerCrop"

Here is a full list of available scale types: http://developer.android.com/reference/android/widget/ImageView.ScaleType.html

回答6:

Try using InsetDrawable (worked well for me).

Just give this your drawable, and insets (or padding) you want from either of the four sides.

InsetDrawable insetDrawable = new InsetDrawable(drawable, insetLeft, insetTop, insetRight, insetBottom);

It is specifically used for setting background drawable, of size smaller or than the View.

See Here : https://developer.android.com/reference/android/graphics/drawable/InsetDrawable.html

回答7:

Old question, but none of the other answers worked for me. This xml code did however:

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentTop="true"
        android:scaleType="centerCrop"
        android:src="@drawable/background_image"/> 

</RelativeLayout>

回答8:

If your bitmap is wider than it is tall, use android:gravity="fill_vertical". Otherwise, use android:gravity="fill_horizontal". This has a similar effect as using android:scaleType="centerCrop" on an ImageView.

<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:gravity="fill_vertical"
    android:src="@drawable/image" />

If you support multiple orientations, you can create one bitmap XML file in the drawable-port folder and the other in the drawable-land folder.

回答9:

In order to fit the image to the available space (or if you have set width and height in dp), I have tried this approach if the image is not too wide.

Here I have set same width and height for square images [or you can wrap_content on both].

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ImageView
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_alignParentTop="true"
        android:adjustViewBounds="true"
        android:scaleType="fitCenter"
        android:src="@drawable/background_image"/> 

</RelativeLayout>

adjust view bounds and scale type center fit do the trick.