Android自定义View的学习(二)

MainActivity如下:

package cc.testviewstudy2;

import android.os.Bundle;
import android.app.Activity;
/**
 * Demo描述:
 * 关于自定义View的学习(二)
 * 
 * View的绘制流程:onMeasure()-->onLayout()-->onDraw()
 * 
 * 学习资料:
 * http://blog.csdn.net/guolin_blog/article/details/16330267
 * Thank you very much
 * 
 */
public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
	}

}

LinearLayoutTest如下:

package cc.testviewstudy2;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
import android.widget.LinearLayout;
/**
 * 注意:
 * 1 继承自XXXXLayout不要继承自ViewGroup
 *   假如继承自ViewGroup那么xml的cc.testviewstudy2.ViewGroupLayout中
 *   设置layout_width和layout_height不论是wrap_content还是fill_parent
 *   这个父视图总是充满屏幕的.
 *   现象是如此,原因暂不明.
 *   
 * 2 在本LinearLayoutTest我们只放入一个子View作为测试
 */
public class LinearLayoutTest extends LinearLayout {
    private Paint mPaint;
	public LinearLayoutTest(Context context) {
		super(context);
	}

	public LinearLayoutTest(Context context, AttributeSet attrs) {
		super(context, attrs);
	}
	
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
		if (getChildCount()>0) {
			View childView=getChildAt(0);
			//这里的widthMeasureSpec和heightMeasureSpec都是父视图的
			//这两个值都由Size和Mode组成,所以要是如下输出:
			//System.out.println("widthMeasureSpec="+widthMeasureSpec+",heightMeasureSpec="+heightMeasureSpec);
			//会得到两个很大的值.这个值就是Size和Mode的组合.
			//所以我们应该按照下面的方式来
			//分别获取widthMeasureSpec和heightMeasureSpec的Size和Mode
			int widthSize=MeasureSpec.getSize(widthMeasureSpec);
			int widthMode=MeasureSpec.getMode(widthMeasureSpec);
			int heightSize=MeasureSpec.getSize(heightMeasureSpec);
			int heightMode=MeasureSpec.getMode(heightMeasureSpec);
			System.out.println("父视图widthSize="+widthSize+",父视图widthMode="+widthMode+
					           ",父视图heightSize="+heightSize+",父视图heightMode="+heightMode);
			//测量子View
			measureChild(childView, widthMeasureSpec, heightMeasureSpec);
		}
	}

	@Override
	protected void onLayout(boolean arg0, int arg1, int arg2, int arg3, int arg4) {
		if (getChildCount()>0) {
			View childView=getChildAt(0);
			System.out.println("子视图childView.getMeasuredWidth()="+childView.getMeasuredWidth()+
					           ",子视图childView.getMeasuredHeight()="+ childView.getMeasuredHeight());
			//摆放子View
			childView.layout(0, 0, childView.getMeasuredWidth(), childView.getMeasuredHeight());
			//X和Y均平移50
			//在此犯错写成了:childView.layout(50, 50, childView.getMeasuredWidth(), childView.getMeasuredHeight());
			//导致图片显示出来很小,正确的方式如下:
			//childView.layout(50, 50, childView.getMeasuredWidth()+50, childView.getMeasuredHeight()+50);
		}

	}
	
	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		mPaint = new Paint();
		mPaint.setColor(Color.YELLOW);
		mPaint.setTextSize(20);
		String content = "Hello World";
		canvas.drawText(content, 150, 100, mPaint);

	}

}

main.xml如下:

<cc.testviewstudy2.LinearLayoutTest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#ff0033"
     >

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />

</cc.testviewstudy2.LinearLayoutTest>