Canvas的save()和restore()以及clipRect()方法测试

MainActivity如下:

package cn.testcanvas;
import android.os.Bundle;
import android.widget.ImageView;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
/**
 * Demo描述:
 * canvas的save()和restore()以及clipRect()方法测试
 *
 * Demo总结:
 * 1 save()和restore()要配对使用(restore可以比save少,但不能多)
 *   若restore调用次数比save多,会报错
 * 2 canvas剪裁后绘制的东西只能在裁剪区域的范围能才能显示出来
 *
 * 参考资料:
 * http://blog.csdn.net/lonelyroamer/article/details/8264189
 *
 *
 */
public class MainActivity extends Activity {
    private ImageView mImageView;
    private ImageView mClipedImageView;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		init();
	}
    private void init(){
    	mImageView=(ImageView) findViewById(R.id.imageView);
    	mClipedImageView=(ImageView) findViewById(R.id.clipedImageView);
    	//分开测试
    	//testClip();
    	testSaveAndRestore();
    }

    private void testClip(){
    	Bitmap bitmap=Bitmap.createBitmap(200, 200, Config.ARGB_8888);
    	Canvas canvas=new Canvas(bitmap);
    	canvas.drawColor(Color.GREEN);
    	Paint paint=new Paint();
    	paint.setColor(Color.YELLOW);
    	canvas.drawText("绿色部分为Canvas剪切前的区域", 20, 50, paint);

    	Rect rect=new Rect(10,95,180,140);
    	canvas.clipRect(rect);
    	canvas.drawColor(Color.YELLOW);
    	paint.setColor(Color.BLACK);
    	//canvas剪裁后绘制的东西只能在裁剪区域的范围能才能显示出来
    	canvas.drawText("黄色部分为Canvas剪切后的区域", 10, 110, paint);
    	mImageView.setImageBitmap(bitmap);

    	//显示截取后的Bitmap:
    	Bitmap newBitmap=Bitmap.createBitmap(bitmap,10,95,170,45);
    	mClipedImageView.setImageBitmap(newBitmap);

    }

    private void testSaveAndRestore(){
    	Bitmap bitmap=Bitmap.createBitmap(200, 200, Config.ARGB_8888);
    	Canvas canvas=new Canvas(bitmap);
    	Paint paint=new Paint();
    	paint.setColor(Color.RED);
    	paint.setTextSize(25);
    	canvas.rotate(15);
    	canvas.drawText("Hello Android 1", 20, 30, paint);
    	canvas.translate(50, 50);
    	//注意:save()方法
    	//保存在此save()方法之前的canvas的操作
    	//比如:roate(),translate(),clipXXX()
    	canvas.save();

    	paint.setColor(Color.GREEN);
    	paint.setTextSize(15);
    	canvas.rotate(60);
    	canvas.translate(-20,-20);
    	canvas.drawText("Hello Android 2", 20, 60, paint);

    	//注意:restore()方法将save()方法之
    	//后Canvas的roate(),translate(),clipXXX()的操作清空
    	canvas.restore();
    	paint.setColor(Color.BLACK);
    	paint.setTextSize(15);
    	canvas.drawText("Hello Android 3", 20, 70, paint);

    	mImageView.setImageBitmap(bitmap);

    }
}

main.xml如下:

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="测试Canvas"
        android:layout_centerHorizontal="true"
    />
    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/textView"
        android:layout_centerInParent="true"
     />
    <ImageView
        android:id="@+id/clipedImageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/imageView"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="15dip"
     />

</RelativeLayout>