将图像调整到ImageView中，保持纵横比，然后将ImageView调整为图像尺寸。

(The answer was heavily modified after clarifications to the original question)

After clarifications:
This cannot be done in xml only. It is not possible to scale both the image and the ImageView so that image's one dimension would always be 250dp and the ImageView would have the same dimensions as the image.

This code scales Drawable of an ImageView to stay in a square like 250dp x 250dp with one dimension exactly 250dp and keeping the aspect ratio. Then the ImageView is resized to match the dimensions of the scaled image. The code is used in an activity. I tested it via button click handler.

Enjoy. :)

private void scaleImage(ImageView view) throws NoSuchElementException  {
// Get bitmap from the the ImageView.
Bitmap bitmap = null;


try {
Drawable drawing = view.getDrawable();
bitmap = ((BitmapDrawable) drawing).getBitmap();
} catch (NullPointerException e) {
throw new NoSuchElementException("No drawable on given view");
} catch (ClassCastException e) {
// Check bitmap is Ion drawable
bitmap = Ion.with(view).getBitmap();
}


// Get current dimensions AND the desired bounding box
int width = 0;


try {
width = bitmap.getWidth();
} catch (NullPointerException e) {
throw new NoSuchElementException("Can't find bitmap on given view/drawable");
}


int height = bitmap.getHeight();
int bounding = dpToPx(250);
Log.i("Test", "original width = " + Integer.toString(width));
Log.i("Test", "original height = " + Integer.toString(height));
Log.i("Test", "bounding = " + Integer.toString(bounding));


// Determine how much to scale: the dimension requiring less scaling is
// closer to the its side. This way the image always stays inside your
// bounding box AND either x/y axis touches it.
float xScale = ((float) bounding) / width;
float yScale = ((float) bounding) / height;
float scale = (xScale <= yScale) ? xScale : yScale;
Log.i("Test", "xScale = " + Float.toString(xScale));
Log.i("Test", "yScale = " + Float.toString(yScale));
Log.i("Test", "scale = " + Float.toString(scale));


// Create a matrix for the scaling and add the scaling data
Matrix matrix = new Matrix();
matrix.postScale(scale, scale);


// Create a new bitmap and convert it to a format understood by the ImageView
Bitmap scaledBitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
width = scaledBitmap.getWidth(); // re-use
height = scaledBitmap.getHeight(); // re-use
BitmapDrawable result = new BitmapDrawable(scaledBitmap);
Log.i("Test", "scaled width = " + Integer.toString(width));
Log.i("Test", "scaled height = " + Integer.toString(height));


// Apply the scaled bitmap
view.setImageDrawable(result);


// Now change ImageView's dimensions to match the scaled image
LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) view.getLayoutParams();
params.width = width;
params.height = height;
view.setLayoutParams(params);


Log.i("Test", "done");
}


private int dpToPx(int dp) {
float density = getApplicationContext().getResources().getDisplayMetrics().density;
return Math.round((float)dp * density);
}

The xml code for the ImageView:

<ImageView a:id="@+id/image_box"
a:background="#ff0000"
a:src="@drawable/star"
a:layout_width="wrap_content"
a:layout_height="wrap_content"
a:layout_marginTop="20dp"
a:layout_gravity="center_horizontal"/>

Thanks to this discussion for the scaling code:
http://www.anddev.org/resize_and_rotate_image_-_example-t621.html

UPDATE 7th, November 2012:
Added null pointer check as suggested in comments

try adding android:scaleType="fitXY" to your ImageView.

May not be answer for this specific question, but if someone is, like me, searching for answer how to fit image in ImageView with bounded size (for example, maxWidth) while preserving Aspect Ratio and then get rid of excessive space occupied by ImageView, then the simplest solution is to use the following properties in XML:

    android:scaleType="centerInside"
android:adjustViewBounds="true"

<ImageView android:layout_width="match_parent"
android:layout_height="wrap_content"
android:scaleType="centerCrop"
android:adjustViewBounds="true"/>

The Below code make the bitmap perfectly with same size of the imageview. Get the bitmap image height and width and then calculate the new height and width with the help of imageview's parameters. That give you required image with best aspect ratio.

int currentBitmapWidth = bitMap.getWidth();
int currentBitmapHeight = bitMap.getHeight();


int ivWidth = imageView.getWidth();
int ivHeight = imageView.getHeight();
int newWidth = ivWidth;


newHeight = (int) Math.floor((double) currentBitmapHeight *( (double) new_width / (double) currentBitmapWidth));


Bitmap newbitMap = Bitmap.createScaledBitmap(bitMap, newWidth, newHeight, true);


imageView.setImageBitmap(newbitMap)

enjoy.

After searching for a day, I think this is the easiest solution:

imageView.getLayoutParams().width = 250;
imageView.getLayoutParams().height = 250;
imageView.setAdjustViewBounds(true);

Edited Jarno Argillanders answer:

How to fit Image with your Width and Height:

1) Initialize ImageView and set Image:

iv = (ImageView) findViewById(R.id.iv_image);
iv.setImageBitmap(image);

2) Now resize:

scaleImage(iv);

Edited scaleImage method: (you can replace EXPECTED bounding values)

private void scaleImage(ImageView view) {
Drawable drawing = view.getDrawable();
if (drawing == null) {
return;
}
Bitmap bitmap = ((BitmapDrawable) drawing).getBitmap();


int width = bitmap.getWidth();
int height = bitmap.getHeight();
int xBounding = ((View) view.getParent()).getWidth();//EXPECTED WIDTH
int yBounding = ((View) view.getParent()).getHeight();//EXPECTED HEIGHT


float xScale = ((float) xBounding) / width;
float yScale = ((float) yBounding) / height;


Matrix matrix = new Matrix();
matrix.postScale(xScale, yScale);


Bitmap scaledBitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
width = scaledBitmap.getWidth();
height = scaledBitmap.getHeight();
BitmapDrawable result = new BitmapDrawable(context.getResources(), scaledBitmap);


view.setImageDrawable(result);


LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) view.getLayoutParams();
params.width = width;
params.height = height;
view.setLayoutParams(params);
}

And .xml:

<ImageView
android:id="@+id/iv_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal" />

Use this code:

<ImageView android:id="@+id/avatar"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:scaleType="fitXY" />

this can all be done using XML... the other methods seem pretty complicated. Anyway, you just set the height to what ever you want in dp, then set the width to wrap content or visa versa. Use scaleType fitCenter to adjust the size of the image.

<ImageView
android:layout_height="200dp"
android:layout_width="wrap_content"
android:scaleType="fitCenter"
android:adjustViewBounds="true"
android:src="@mipmap/ic_launcher"
android:layout_below="@+id/title"
android:layout_margin="5dip"
android:id="@+id/imageView1">

This did it for my case.

<ImageView android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:scaleType="centerCrop"
android:adjustViewBounds="true" />

I needed to get this done in a constraint layout with Picasso, so I munged together some of the above answers and came up with this solution (I already know the aspect ratio of the image I'm loading, so that helps):

Called in my activity code somewhere after setContentView(...)

protected void setBoxshotBackgroundImage() {
ImageView backgroundImageView = (ImageView) findViewById(R.id.background_image_view);


if(backgroundImageView != null) {
DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
int width = displayMetrics.widthPixels;
int height = (int) Math.round(width * ImageLoader.BOXART_HEIGHT_ASPECT_RATIO);


// we adjust the height of this element, as the width is already pinned to the parent in xml
backgroundImageView.getLayoutParams().height = height;


// implement your Picasso loading code here
} else {
// fallback if no element in layout...
}
}

In my XML

<?xml version="1.0" encoding="utf-8"?>


<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:layout_editor_absoluteY="0dp"
tools:layout_editor_absoluteX="0dp">


<ImageView
android:id="@+id/background_image_view"
android:layout_width="0dp"
android:layout_height="0dp"
android:scaleType="fitStart"
app:srcCompat="@color/background"
android:adjustViewBounds="true"
tools:layout_editor_absoluteY="0dp"
android:layout_marginTop="0dp"
android:layout_marginBottom="0dp"
android:layout_marginRight="0dp"
android:layout_marginLeft="0dp"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"/>


<!-- other elements of this layout here... -->


</android.support.constraint.ConstraintLayout>

Note the lack of a constraintBottom_toBottomOf attribute. ImageLoader is my own static class for image loading util methods and constants.

I needed to have an ImageView and an Bitmap, so the Bitmap is scaled to ImageView size, and size of the ImageView is the same of the scaled Bitmap :).

I was looking through this post for how to do it, and finally did what I want, not the way described here though.

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/acpt_frag_root"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/imageBackground"
android:orientation="vertical">


<ImageView
android:id="@+id/acpt_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:adjustViewBounds="true"
android:layout_margin="@dimen/document_editor_image_margin"
android:background="@color/imageBackground"
android:elevation="@dimen/document_image_elevation" />

and then in onCreateView method

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {


View view = inflater.inflate(R.layout.fragment_scanner_acpt, null);


progress = view.findViewById(R.id.progress);


imageView = view.findViewById(R.id.acpt_image);
imageView.setImageBitmap( bitmap );


imageView.getViewTreeObserver().addOnGlobalLayoutListener(()->
layoutImageView()
);


return view;
}

and then layoutImageView() code

private void layoutImageView(){


float[] matrixv = new float[ 9 ];


imageView.getImageMatrix().getValues(matrixv);


int w = (int) ( matrixv[Matrix.MSCALE_X] * bitmap.getWidth() );
int h = (int) ( matrixv[Matrix.MSCALE_Y] * bitmap.getHeight() );


imageView.setMaxHeight(h);
imageView.setMaxWidth(w);


}

And the result is that image fits inside perfectly, keeping aspect ratio, and doesn't have extra leftover pixels from ImageView when the Bitmap is inside.

Result

It's important ImageView to have wrap_content and adjustViewBounds to true, then setMaxWidth and setMaxHeight will work, this is written in the source code of ImageView,

/*An optional argument to supply a maximum height for this view. Only valid if
* {@link #setAdjustViewBounds(boolean)} has been set to true. To set an image to be a
* maximum of 100 x 100 while preserving the original aspect ratio, do the following: 1) set
* adjustViewBounds to true 2) set maxWidth and maxHeight to 100 3) set the height and width
* layout params to WRAP_CONTENT. */

The Best solution that works in most cases is

Here is an example:

<ImageView android:id="@+id/avatar"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitXY"/>

I am using a very simple solution. Here my code:

imageView.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT,LinearLayout.LayoutParams.MATCH_PARENT));
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
imageView.getLayoutParams().height = imageView.getLayoutParams().width;
imageView.setMinimumHeight(imageView.getLayoutParams().width);

My pictures are added dynamically in a gridview. When you make these settings to the imageview, the picture can be automatically displayed in 1:1 ratio.

Use Simple math to resize the image . either you can resize ImageView or you can resize drawable image than set on ImageView . find the width and height of your bitmap which you want to set on ImageView and call the desired method. suppose your width 500 is greater than height than call method

//250 is the width you want after resize bitmap
Bitmat bmp = BitmapScaler.scaleToFitWidth(bitmap, 250) ;
ImageView image = (ImageView) findViewById(R.id.picture);
image.setImageBitmap(bmp);

You use this class for resize bitmap.

public class BitmapScaler{
// Scale and maintain aspect ratio given a desired width
// BitmapScaler.scaleToFitWidth(bitmap, 100);
public static Bitmap scaleToFitWidth(Bitmap b, int width)
{
float factor = width / (float) b.getWidth();
return Bitmap.createScaledBitmap(b, width, (int) (b.getHeight() * factor), true);
}




// Scale and maintain aspect ratio given a desired height
// BitmapScaler.scaleToFitHeight(bitmap, 100);
public static Bitmap scaleToFitHeight(Bitmap b, int height)
{
float factor = height / (float) b.getHeight();
return Bitmap.createScaledBitmap(b, (int) (b.getWidth() * factor), height, true);
}
}

xml code is

<ImageView
android:id="@+id/picture"
android:layout_width="250dp"
android:layout_height="250dp"
android:layout_gravity="center_horizontal"
android:layout_marginTop="20dp"
android:adjustViewBounds="true"
android:scaleType="fitcenter" />

if it's not working for you then replace android:background with android:src

android:src will play the major trick

    <ImageView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:scaleType="fitCenter"
android:src="@drawable/bg_hc" />

it's working fine like a charm

Quick answer:

<ImageView
android:id="@+id/imageView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:scaleType="center"
android:src="@drawable/yourImage"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />

Just write it in xml

android:scaleType="centerCrop"

Worked for me

In my case, I found the answer buried in a comment on this question (credit to @vida).

android:scaleType="centerInside"

How about using android:scaleType="centerInside" instead of android:scaleType="centerCrop"? It would also not crop the image but ensure that both width and height are less than or equal the imageview's width and height :) Here's a good visual guide for scaletypes: Android ImageView ScaleType: A Visual Guide

I just use ImageView inside ConstraintLayout and set adjustviewbound in ImageView to true.

<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">


<ImageView
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:src="@drawable/myimg"
android:adjustViewBounds="true"
/>


</androidx.constraintlayout.widget.ConstraintLayout>