自定义ViewGroup-通过内边距加深理解

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 读取 4 个方向的
 padding：

 public int getPaddingLeft () 离左边的 padding

 public int getPaddingRight () 离右边的 padding

 public int getPaddingTop () 离顶部的 padding

 public int getPaddingRight () 离底部的 padding

CustomViewGroup3：

public class CustomViewGroup3 extends ViewGroup {
    public CustomViewGroup3(Context context) {
        super(context);
    }

    public CustomViewGroup3(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CustomViewGroup3(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //测量所有的子View
        measureChildren(widthMeasureSpec, heightMeasureSpec);
        //测量自己的宽高
        int width = measureWidth(widthMeasureSpec);
        int height = measureHeight(heightMeasureSpec);

        setMeasuredDimension(width, height);
    }

    private int measureHeight(int widthMeasureSpec) {
        //父控件建议自己测量的值
        int measureMode = MeasureSpec.getMode(widthMeasureSpec);
        int measureSize = MeasureSpec.getSize(widthMeasureSpec);

        int width = 0;

        if (measureMode == MeasureSpec.EXACTLY) {
            width = measureSize;
        } else if (measureMode == MeasureSpec.AT_MOST) {
            int aWidth = 0;
            int bWidth = 0;
            int cWidth = 0;
            int dWidth = 0;

            for (int i = 0; i < getChildCount(); i++) {
                if (i == 0) {
                    aWidth = getChildAt(i).getMeasuredWidth();//左边View的宽度
                } else if (i == 1) {
                    bWidth = getChildAt(i).getMeasuredWidth();
                } else if (i == 2) {
                    cWidth = getChildAt(i).getMeasuredWidth();
                } else if (i == 3) {
                    dWidth = getChildAt(i).getMeasuredWidth();
                }
            }
            //getPaddingTop：top离top的内边距   getPaddingBottom：bottom离底的内边距
            width = Math.max(aWidth, bWidth) + Math.max(cWidth, dWidth)
                    + getPaddingTop() + getPaddingBottom();//取到宽度的最大值
        }
        return width;
    }

    private int measureWidth(int heightMeasureSpec) {
        int measureMode = MeasureSpec.getMode(heightMeasureSpec);
        int measureSize = MeasureSpec.getSize(heightMeasureSpec);

        int height = 0;

        if (measureMode == MeasureSpec.EXACTLY) {
            height = measureSize;
        } else if (measureMode == MeasureSpec.AT_MOST) {
            int aHeight = 0;
            int bHeight = 0;
            int cHeight = 0;
            int dHeight = 0;

            for (int i = 0; i < getChildCount(); i++) {
                if (i == 0) {
                    aHeight = getChildAt(i).getMeasuredHeight();
                } else if (i == 1) {
                    bHeight = getChildAt(i).getMeasuredHeight();
                } else if (i == 2) {
                    cHeight = getChildAt(i).getMeasuredHeight();
                } else if (i == 3) {
                    dHeight = getChildAt(i).getMeasuredHeight();
                }
            }
            height = Math.max(aHeight, bHeight) + Math.max(cHeight, dHeight)
                    + getPaddingLeft() + getPaddingRight();//取到宽度的最大值
        }
        return height;
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int leftPadding = getPaddingLeft();
        int rightPadding = getPaddingRight();
        int topPadding = getPaddingTop();
        int bottomPadding = getPaddingBottom();

        for (int i = 0; i < getChildCount(); i++) {
            View childView = getChildAt(i);//某一个子View

            if (i == 0) {
                childView.layout(leftPadding,
                        topPadding,
                        childView.getMeasuredWidth() + leftPadding,
                        childView.getMeasuredHeight() + topPadding);
            } else if (i == 1) {
                childView.layout(getMeasuredWidth() - childView.getMeasuredWidth() - rightPadding,
                        topPadding,
                        getMeasuredWidth() - rightPadding,
                        childView.getMeasuredHeight() + topPadding);
            } else if (i == 2) {
                childView.layout(leftPadding,
                        getMeasuredHeight() - childView.getMeasuredHeight() - bottomPadding,
                        childView.getMeasuredWidth() + leftPadding,
                        getMeasuredHeight() - bottomPadding);
            } else if (i == 3) {
                childView.layout(getMeasuredWidth() - childView.getMeasuredWidth() - rightPadding,
                        getMeasuredHeight() - childView.getMeasuredHeight() - bottomPadding,
                        getMeasuredWidth() - rightPadding,
                        getMeasuredHeight() - bottomPadding);
            }
        }
    }
}

activity_main：

<com.example.user.myapplication4.CustomViewGroup3
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FFCCCCCC"
        android:paddingBottom="15dp"
        android:paddingLeft="20dp"
        android:paddingRight="30dp"
        android:paddingTop="10dp">

        <TextView
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:background="@android:color/holo_blue_bright" />

        <TextView
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:background="@android:color/holo_blue_dark" />

        <TextView
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:background="@android:color/holo_red_dark" />

        <TextView
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:background="@android:color/holo_green_light" />
</com.example.user.myapplication4.CustomViewGroup3>

结果展示：