一个简单onDraw的demo

重写View.onDraw获得canvas的对象View中的Canvas对象会被当做参数传递过来，我们操作这个Canvas，效果会直接反应在View中。

public class TestActivity extends Activity implements OnClickListener {
	private MyCountdownView view;
	private Button startBtn;
	private int count = 1;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_map_test);
		view = (MyCountdownView) findViewById(R.id.myCountdownView);
		startBtn = (Button) findViewById(R.id.button_test_start);

		startBtn.setOnClickListener(this);
	}

	@Override
	public void onClick(View arg0) {

		new Thread(new Runnable() {
			@Override
			public void run() {
				try {
					while (count <10) {
						count++;
						Thread.sleep(1000);
						view.setTxtCount(count);
					}
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}).start();
	}
}

</pre><pre name="code" class="java">public class MyCountdownView extends View {
	private int textSize;
	private int mCount=1;
	private Paint textPoint;
	
	public MyCountdownView(Context context) {
		super(context);
		initView();
	}

	public MyCountdownView(Context context, AttributeSet attrs) {
		super(context, attrs);
		initView();
	}

	public MyCountdownView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		initView();
	}
	
	public void setTxtCount(int mCount){
		this.mCount=mCount;
        //// 使用postInvalidate可以直接在线程中更新界面
		postInvalidate();
	}
	
	private void initView(){
		textSize=dip2px(getContext(), 100);
		textPoint=new Paint(Paint.LINEAR_TEXT_FLAG);
		textPoint.setAntiAlias(true);
		textPoint.setColor(Color.parseColor("#000000"));
		textPoint.setStyle(Style.FILL_AND_STROKE);
		textPoint.setTextAlign(Align.LEFT);
		textPoint.setTextSize(textSize);
	}
	
	@Override
	public void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		Rect bounds=new Rect();
		String middleText=String.valueOf(mCount);
		textPoint.getTextBounds(middleText, 0, middleText.length(), bounds);
		canvas.drawText(middleText, getWidth()/2-60, getHeight()/2, textPoint);
	}
	//dip与px的互相转换：
	public static int dip2px(Context context, float dipValue) {  
        final float scale = context.getResources().getDisplayMetrics().density;  
        return (int) (dipValue * scale + 0.5f);  
    }
}