android自定义控件(七) 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