View.onDraw(Canvas canvas)的使用_android 在 rootview canvas

View通过View.onDraw(Canvas canvas)来Draw.

我们可以定义自己的继承于View的TestView,然后重载View.onDraw(Canvas canvas).

对于自定义的TestView如何与Activity关联？有以下两种方式：

1. 直接在setContentView(View view)里面加进去自定义的View：setContentView(new TestView(this)).
2. 另外，可以在layout文件里面可以使用自定义的View(如何自定义的View为内部类，就会失效)，如：

<?xml version="1.0" encoding="utf-8"?> <FrameLayout android:layout_width="fill_parent" android:layout_height="fill_parent" xmlns:android="http://schemas.android.com/apk/res/android"> <com.android.test.TestView android:id="@+id/testview" android:layout_width="fill_parent" android:layout_height="fill_parent"/> </FrameLayout>

以下为使用onDraw(Canvas canvas)画矩形区域，及在其上画文本的实例（通过使用内部类使程序显得更加简洁，紧凑）：

package com.android.test; import android.app.Activity; import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Rect; import android.graphics.Typeface; import android.os.Bundle; import android.view.View; public class TestActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(new TestView(this)); } public class TestView extends View { private Paint mPaint = new Paint(); public TestView(Context context) { super(context); } @Override protected void onDraw(Canvas canvas) { // TODO Auto-generated method stub super.onDraw(canvas); String text = "Android - 机器人"; mPaint.setColor(Color.WHITE); Paint paint = new Paint(); paint.setColor(Color.RED); String familyName = "宋体"; Typeface font = Typeface.create(familyName,Typeface.BOLD); paint.setTypeface(font); paint.setTextSize(22); canvas.drawRect(new Rect(0, 0, 320, 240), mPaint); canvas.drawText(text, 0, 100, paint); } } }

运行效果如下图：