横幅を最大に広げた状態で縦を調整するImageView。Androidのlayout_weight="1"のエリアの下に配置するフッター画像などで使用します。

layout.xml

    <package_name.widget.WidthAdjustImageView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:contentDescription="@null"
        android:scaleType="fitCenter"
        android:src="@drawable/foot_banner" />

WidthAdjustImageView.java

import android.content.Context;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.widget.ImageView;

public class WidthAdjustImageView extends ImageView {

    public WidthAdjustImageView(Context context) {
        this(context, null);
    }

    public WidthAdjustImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public WidthAdjustImageView(Context context, AttributeSet attrs,
            int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        Drawable drawable = this.getDrawable();
        Rect rect = drawable.getBounds();
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = (int) (rect.height() * ((float) width / (float) rect
                .width()));
        setMeasuredDimension(width, height);
    }

}