自定义View和自定义ViewGroup实例讲解

参考:https://www.jianshu.com/p/c84693096e41

自定义View

定义一个自定义View的步骤:

1.需要继承View或者View的子类;

2.重写至少两个构造方法;

3.自定义xml中的属性;

declare-styleable中的format的类型:

reference:引用类型,如@drawable/xxx

color:颜色,如#fff000

dimension:尺寸,如11dp

其他的:float,integer,boolean,string

4.在构造方法中对属性进行赋值;

5.onMeasure方法;

测量当前View

6.onDraw方法;

对View的绘制

下面的例子是一个外侧是正方形内侧为圆形的自定义View

在res中values中新建一个styles.xml,里面写

public class MyView extends View {
    private int defaultSize;
    private int circleColor;
    private Paint paint = new Paint();//在onDraw中会使用,但在onDraw中定义的话会频繁新建,因此放在外面定义

    public MyView(Context context) {
        super(context);
    }

    public MyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        //获取属性
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.MyView);
        defaultSize = (int) typedArray.getDimension(R.styleable.MyView_default_size, 100);
        circleColor = typedArray.getColor(R.styleable.MyView_circle_color, getResources().getColor(R.color.black));
        typedArray.recycle();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = getSize(defaultSize, widthMeasureSpec);
        int height = getSize(defaultSize, heightMeasureSpec);
        height = width = Math.min(width, height);//将宽和高的小的值边长
        setMeasuredDimension(width, height);//设置最后的宽高
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int radius = getMeasuredWidth() / 2;
        //这个x,y是针对view自身的
        int centerX = radius;
        int centerY = radius;
        paint.setColor(circleColor);
        paint.setAntiAlias(true);//抗锯齿
        canvas.drawCircle(centerX, centerY, radius, paint);
    }

    private int getSize(int defaultSize, int measureSpec) {
        int mySize;
        int mode = MeasureSpec.getMode(measureSpec);
        int size = MeasureSpec.getSize(measureSpec);
        switch (mode) {
            case MeasureSpec.EXACTLY:
            case MeasureSpec.AT_MOST:
                //当为wrap_content或者match_parent,就按系统的去走
                mySize = size;
                break;
            case MeasureSpec.UNSPECIFIED:
                mySize = defaultSize;
                break;
            default:
                throw new IllegalStateException("Unexpected value: " + mode);
        }
        return mySize;
    }
}

xml中使用:

 

自定义ViewGroup

自定义ViewGroup的步骤

1.构造方法

2.onlayout必须重写

作用:确定子View的位置

3.onMeasure

作用:确定自定义的ViewGroup的宽高

public class MyViewGroup extends LinearLayout {
    public MyViewGroup(Context context) {
        super(context);
    }

    public MyViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    //必实现
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int count = getChildCount();
        int curHeight = 0;//当前总高度
        for (int i = 0; i < count; i++) {
            View childView = getChildAt(i);
            int childWidth = childView.getMeasuredWidth();
            int childHeight = childView.getMeasuredHeight();
            LinearLayout.LayoutParams lp = (LayoutParams) childView.getLayoutParams();
            //加上margin值
            childView.layout(l + lp.leftMargin, curHeight + lp.topMargin, l + lp.leftMargin + childWidth, curHeight + childHeight + lp.topMargin);
            curHeight += childHeight + lp.topMargin;
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //对所有的子View进行测量,触发每一个子View的onMeasure函数
        //子view的测量方法在子view里面去自定义,和这里的onMeasure没关系
        measureChildren(widthMeasureSpec, heightMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int count = getChildCount();
        if (count == 0) {
            setMeasuredDimension(0, 0);
        } else {//对wrap_content的特殊处理
            if (widthMode == MeasureSpec.AT_MOST && heightMode == MeasureSpec.AT_MOST) {
                setMeasuredDimension(getMaxChildWidth(), totalChildHeight());
            } else if (widthMode == MeasureSpec.AT_MOST) {
                setMeasuredDimension(getMaxChildWidth(), heightMeasureSpec);
            } else if (heightMode == MeasureSpec.AT_MOST) {
                setMeasuredDimension(widthMeasureSpec, totalChildHeight());
            }
        }
    }

    //返回所有子View宽度的最大值
    private int getMaxChildWidth() {
        int count = getChildCount();
        int maxWidth = 0;
        for (int i = 0; i < count; i++) {
            LinearLayout.LayoutParams lp = (LayoutParams) getChildAt(i).getLayoutParams();
            maxWidth = Math.max(getChildAt(i).getMeasuredWidth() + lp.leftMargin + lp.rightMargin, maxWidth);//加上左右margin
        }
        return maxWidth;
    }

    //返回所有子View的高度的总和
    private int totalChildHeight() {
        int count = getChildCount();
        int totalHeight = 0;
        for (int i = 0; i < count; i++) {
            LinearLayout.LayoutParams lp = (LayoutParams) getChildAt(i).getLayoutParams();
            totalHeight += getChildAt(i).getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
        }
        return totalHeight;
    }
}