自定义按比例显示的ImageView

1，实现效果

按比例显示的ImageView

2，实现逻辑

【1】去看服务端给你的图片比例是多少，

宽度/高度计算宽高比。
高:宽 = 1:2.43

自定义按比例显示的ImageView

【1】创建构造方法

public class RatioImageView extends ImageView {}

【2】布局中使用

  <com.heima.googlemarket.ui.view.RatioImageView

            android:id="@+id/iv_image"

            android:layout_width="match_parent"

            android:layout_height="wrap_content"/>

【3】创建自定义属性

Values 创attrs.xml文件

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

<resources>

    <declare-styleable name="RatioImageView">

        <attr name="ratio" format="float"/>

    </declare-styleable>

</resources>

控件布局中使用

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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    android:orientation="vertical"

    android:padding = "5dp"

    android:layout_width="match_parent"

    android:layout_height="wrap_content">

        <com.xiaoshuai.googlemarket.ui.view.RatioImageView

            android:id="@+id/iv_image"

            app:ratio="2.43"

            android:layout_width="match_parent"

            android:layout_height="wrap_content"/>

       

</LinearLayout>

int widthSize = MeasureSpec.getSize(widthMeasureSpec);

//参数1命名空间，参数2自定义属性的属性名，参数3默认值

ratio = attrs.getAttributeFloatValue(NAMESPACE, "ratio", 0.0f);

在onMeasure获取宽度，他一定是一个具体的值，match_parent+5dp是父布局的match_parent，父布局的match_parent

宽度除除以比例等到高度的精确值

int heightSize = (int)(widthSize/ratio+0.5f);

生成具体的32位数高度值进行测量

 heightMeasureSpec = MeasureSpec.makeMeasureSpec(heightSize,MeasureSpec.EXACTLY);

【3】全部代码

/**

* Created by HASEE on 2019/4/6.

* 让此控件的宽高和服务器端返回图片的宽高比例一致

* 高:宽 = 1:2.43

*/

public class RatioImageView extends ImageView {

    private static final String TAG = "RatioImageView";

    public static String NAMESPACE = "http://schemas.android.com/apk/res-auto";

    //从自定义属性中获取到的属性值

    private final float ratio;

    public RatioImageView(Context context, AttributeSet attrs) {

        super(context, attrs);

        ratio = attrs.getAttributeFloatValue(NAMESPACE, "ratio", 0.0f);

        Log.i(TAG,"======================ratio = "+ratio);

    }





    @Override

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        //widthMeasureSpec  32位2机制数字    2位   30位

        //00 01 10 11  4种

        //30位         指定宽度大小

        //MeasureSpec.AT_MOST       至多

        //MeasureSpec.EXACTLY       精确值

        //MeasureSpec.UNSPECIFIED   ListView





        //1.获取自定义控件的宽度具体值

        int widthSize = MeasureSpec.getSize(widthMeasureSpec);

        //2.获取高度值精确值

        int heightSize = (int)(widthSize/ratio+0.5f);

        //3.用精确模式搭配精确值,生成高度的32位数

        heightMeasureSpec = MeasureSpec.makeMeasureSpec(heightSize,MeasureSpec.EXACTLY);





        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

    }

}

自定义按比例显示的ImageView

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