在Android开发中，在Activity中关联视图View是一般使用setContentView方法，该方法一种参数是使用XML资源直接创建：setContentView (int layoutResID)，指定layout中的一个XML的ID即可，这种方法简单。另一个方法是 setContentView(android.view.View)，参数是指定一个视图View对象，这种方法可以使用自定义的视图类。
在一些场合中，需要对View进行一些定制处理，比如获取到Canvas进行图像绘制，需要重载View::onDraw方法，这时需要对View进行派生一个类，重载所需要的方法，然后使用setContentView(Android.view.View)与Activity进行关联，具体代码举例如下：
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public class temp extends Activity {
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/** 在Activity中关联视图view */
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@Override
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public void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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setContentView(new DrawView(this));
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}
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/*自定义类*/
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private class DrawView extends View {
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private Paint paint;
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/**
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* Constructor
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*/
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public DrawView(Context context) {
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super(context);
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paint = new Paint();
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// set's the paint's colour
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paint.setColor(Color.GREEN);
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// set's paint's text size
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paint.setTextSize(25);
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// smooth's out the edges of what is being drawn
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paint.setAntiAlias(true);
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}
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protected void onDraw(Canvas canvas) {
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super.onDraw(canvas);
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canvas.drawText("Hello World", 5, 30, paint);
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// if the view is visible onDraw will be called at some point in the
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// future
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invalidate();
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}
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}
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}
第二个例子，动态绘图
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public class MyAndroidProjectActivity extends Activity {
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/** Called when the activity is first created. */
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/*
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public void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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setContentView(R.layout.main);
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}*/
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static int times = 1;
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/** Called when the activity is first created. */
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@Override
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public void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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setContentView(new DrawView(this));
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}
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private class DrawView extends View {
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Paint vPaint = new Paint();
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private int i = 0;
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public DrawView(Context context) {
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super(context);
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}
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protected void onDraw(Canvas canvas) {
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super.onDraw(canvas);
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System.out.println("this run " + (times++) +" times!");
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// 设定绘图样式
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vPaint.setColor( 0xff00ffff ); //画笔颜色
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vPaint.setAntiAlias( true );//反锯齿
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vPaint.setStyle( Paint.Style.STROKE );
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// 绘制一个弧形
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canvas.drawArc(new RectF(60, 120, 260, 320), 0, i, true, vPaint );
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// 弧形角度
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if( (i+=10) > 360 )
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i = 0;
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// 重绘, 再一次执行onDraw 程序
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invalidate();
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}
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}
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}
