android自定义控件(七) onMeasure() 测量尺寸

转自：/article/1387432.html

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

[html] view
plaincopy

<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

[java] view
plaincopy

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