自定義ViewGroup

時間 2019-12-02

標籤自定義 viewgroup 简体版

原文原文鏈接

關於View的基本知識和如何自定義View請見html

自定義View - http://www.javashuo.com/article/p-bnjbkrpi-bo.htmljava

ViewGroup的職責是啥？

ViewGroup至關於一個放置View的容器，而且咱們在寫佈局xml的時候，會告訴容器（凡是以layout爲開頭的屬性，都是用於告訴容器的），咱們的寬度layout_width、高度layout_height、對齊方式layout_gravity、內邊距layout_maring等。因此ViewGroup的智能爲：給childView計算出建議的寬和高的測量模式；決定childView的位置。（由於childView寬和高能夠設置爲wrap_content，這樣只有childView才能計算出本身的寬和高，因此這裏給出的建議寬和高）android

View的職責是啥？

View的職責就是根據測量模式和ViewGroup給出的建議的寬和高，計算出本身的寬和高；同事還有個更重要的職責：在ViewGroup爲其指定的區域內繪製本身的形態。canvas

ViewGroup和LayoutParams之間的關係？

每一個ViewGroup須要指定一個LayoutParams，用於肯定它的childView支持哪些屬性。不一樣的ViewGroup指定的LayoutParams是不一樣的，包含的屬性也不盡相同。ide

View的3種測量模式

EXACTLY、AT_MOST、UNSPECIFIED佈局

從API角度進行淺析

上面敘述了ViewGroup和View的職責，下面從API角度進行淺析。this

View須要根據ViewGroup傳入的測量值和模式，對本身寬高進行肯定（onMeasure中完成），而後在onDraw中完成對本身的繪製。spa

ViewGroup須要給View傳入view的測量值和模式（onMeasure中完成），並且對於此ViewGroup的父佈局，本身也須要在onMeasure中完成對本身寬和高的肯定。此外，須要在onLayout中完成對其childView的位置的指定。.net

Demo

定義一個ViewGroup，內部能夠傳入0到4個childView，分別依次顯示在左上角、右上角、左下角、右下角。同時在中央繪製一個圓。code

/**
 * Created by xupeng on 16/12/26.
 */

public class MyCustomViewGroup extends ViewGroup {

    private Paint mPaint;

    public MyCustomViewGroup(Context context) {
        super(context);
        init();
    }

    public MyCustomViewGroup(Context context, AttributeSet attrs) {
//        super(context, attrs);
        this(context);
    }

    private void init() {
        setWillNotDraw(false);
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        /**
         * 得到此ViewGroup上級容器爲其推薦的寬和高,以及計算模式
         */
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);

        // 計算出全部的children的寬和高
        measureChildren(widthMeasureSpec, heightMeasureSpec);

        /**
         * 記錄若是是wrap_content設置的寬和高
         */
        int width = 0;
        int height = 0;

        int cCount = getChildCount();

        int cWidth = 0;
        int cHeight = 0;
        MarginLayoutParams cParams = null;

        // 用於計算左邊兩個childView的高度
        int lHeight = 0;

        // 用於計算右邊兩個childView的高度,最終高度取二者之間大值
        int rHeight = 0;

        // 用於計算上邊兩個childView的寬度
        int tWidth = 0;

        // 用於計算下邊兩個childView的寬度,最重寬度取二者之間大值
        int bWidth = 0;

        /**
         * 根據childView計算得出寬和高,以及設置的margin計算容器的寬和高,主要用於容器是wrap_content時
         */
        for (int i = 0; i < cCount; i++) {
            View childView = getChildAt(i);
            cWidth = childView.getMeasuredWidth();
            cHeight = childView.getMeasuredHeight();
            cParams = (MarginLayoutParams) childView.getLayoutParams();

            // 上面兩個childView
            if (i == 0 || i == 1) {
                tWidth += cWidth + cParams.leftMargin + cParams.rightMargin;
            }

            // 下面兩個childView
            if (i == 2 || i == 3) {
                bWidth += cWidth + cParams.leftMargin + cParams.rightMargin;
            }

            if (i == 0 || i == 2) {
                lHeight += cHeight + cParams.topMargin + cParams.bottomMargin;
            }

            if (i == 1 || i == 3) {
                rHeight += cHeight + cParams.topMargin + cParams.bottomMargin;
            }

        }

        width = Math.max(tWidth, bWidth);
        height = Math.max(lHeight, rHeight);

        setMeasuredDimension((widthMode == MeasureSpec.EXACTLY) ? widthSize : width,
                (heightMode == MeasureSpec.EXACTLY) ? heightSize : height);

//        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int cCount = getChildCount();
        int cWidth = 0;
        int cHeight = 0;
        MarginLayoutParams cParams = null;

        /**
         * 遍歷全部childView根據其寬和高,以及margin進行佈局
         */
        for (int i = 0; i < cCount; i++) {
            View childView = getChildAt(i);
            cWidth = childView.getMeasuredWidth();
            cHeight = childView.getMeasuredHeight();
            cParams = (MarginLayoutParams) childView.getLayoutParams();

            int cl = 0, ct = 0, cb = 0, cr = 0;

            switch (i) {
                case 0:
                    cl = cParams.leftMargin;
                    ct = cParams.topMargin;
                    break;
                case 1:
                    cl = getWidth() - cWidth - cParams.rightMargin;
                    ct = cParams.topMargin;
                    break;
                case 2:
                    cl = cParams.leftMargin;
                    ct = getHeight() - cHeight - cParams.bottomMargin;
                    break;
                case 3:
                    cl = getWidth() - cWidth - cParams.rightMargin;
                    ct = getHeight() - cHeight - cParams.bottomMargin;
                    break;
            }

            cr = cl + cWidth;
            cb = cHeight + ct;
            childView.layout(cl, ct, cr, cb);
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int width = getWidth();
        int measureWidth = getMeasuredWidth();
        requestLayout();
        int measureWidthAndState = getMeasuredWidthAndState();
        canvas.drawCircle(getMeasuredWidth() / 2, getMeasuredHeight() / 2, 100 , mPaint);
//        invalidate();
    }

<?xml version="1.0" encoding="utf-8"?>
<com.gnepux.sdkusage.widget.MyCustomViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_custom_view_group"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffff00"
    tools:context="com.gnepux.sdkusage.activity.CustomViewGroupActivity">

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="1"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#ff0000"/>

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="2"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#00ff00"/>

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="3"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#0000ff"/>

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="4"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#ff00ff"/>

</com.gnepux.sdkusage.widget.MyCustomViewGroup>