android自定义控件 onMeasure() 测量尺寸

上次讲的自定义控件刷新点屏幕的任意地方都会刷新,而且在xml里自定义控件下面放一个textview的话,这个TextView是显示不出来的,不只这个,以前的几个自定义控件都是

为什么呢?今天来讲下onMeasure()

在自定义刷新控件的基础上重写onMeasure方法

根据上一篇自定义组件修改

注释在代码里

 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    >
    <xue.test.CusView3
        android:id="@+id/cusview3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        >
    </xue.test.CusView3>
    <TextView
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="我终于出现了" />
</LinearLayout>

这里的TextView无法显示,想要显示的话,要测量控件的大小

 

 

public class CusView3 extends View {

    private int color = 0;
    private String text = "点击我刷新";
    private Paint mPaint;
    private int mAscent;

    public CusView3(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setStyle(Style.FILL);
        mPaint.setTextSize(35.0f);
        setPadding(20, 60, 0, 0); //设置padding
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (color > 2) {
            color = 0;
        }
        switch (color) {
        case 0:
            mPaint.setColor(Color.GREEN);
            break;
        case 1:
            mPaint.setColor(Color.RED);
            break;
        case 2:
            mPaint.setColor(Color.BLUE);
            break;

        default:
            break;
        }

        canvas.drawText(text, getPaddingLeft(), getPaddingTop(), mPaint);
    }

    public void changeColor() {
        color++;
    }

    /**
     * 比onDraw先执行
     *
     * 一个MeasureSpec封装了父布局传递给子布局的布局要求，每个MeasureSpec代表了一组宽度和高度的要求。
     * 一个MeasureSpec由大小和模式组成
     * 它有三种模式：UNSPECIFIED(未指定),父元素部队自元素施加任何束缚，子元素可以得到任意想要的大小;
     *              EXACTLY(完全)，父元素决定自元素的确切大小，子元素将被限定在给定的边界里而忽略它本身大小；
     *              AT_MOST(至多)，子元素至多达到指定大小的值。
     *
     * 　　它常用的三个函数：
     * 1.static int getMode(int measureSpec):根据提供的测量值(格式)提取模式(上述三个模式之一)
     * 2.static int getSize(int measureSpec):根据提供的测量值(格式)提取大小值(这个大小也就是我们通常所说的大小)
     * 3.static int makeMeasureSpec(int size,int mode):根据提供的大小值和模式创建一个测量值(格式)
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(measureWidth(widthMeasureSpec), measureHeight(heightMeasureSpec));
    }

    private int measureWidth(int measureSpec) {
        int result = 0;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            // We were told how big to be
            result = specSize;
        } else {
            // Measure the text
            result = (int) mPaint.measureText(text) + getPaddingLeft() + getPaddingRight();
            if (specMode == MeasureSpec.AT_MOST) {
                // Respect AT_MOST value if that was what is called for by
                // measureSpec
                result = Math.min(result, specSize);// 60,480
            }
        }

        return result;
    }

    private int measureHeight(int measureSpec) {
        int result = 0;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        mAscent = (int) mPaint.ascent();
        if (specMode == MeasureSpec.EXACTLY) {
            // We were told how big to be
            result = specSize;
        } else {
            // Measure the text (beware: ascent is a negative number)
            result = (int) (-mAscent + mPaint.descent()) + getPaddingTop() + getPaddingBottom();
            if (specMode == MeasureSpec.AT_MOST) {
                // Respect AT_MOST value if that was what is called for by
                // measureSpec
                result = Math.min(result, specSize);
            }
        }
        return result;
    }
}

效果图

 

代码 http://download.csdn.net/detail/ethan_xue/4178423