实例讲解Android中的View类以及自定义View控件的方法

TextView textView=(TextView)findViewBy(R.id.textView)

package com.xiong.fisrt_android; 
 
import android.app.Activity; 
import android.graphics.Color; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.TextView; 
 
public class MainActivity extends Activity { 
 
  private TextView textView; 
  private Button button; 
  private int count = 0; 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    textView = (TextView) findViewById(R.id.textView); 
    button = (Button) findViewById(R.id.button); 
    textView.setText("hello Android!!!"); 
    textView.setBackgroundColor(Color.BLUE); 
    ButtoneListener buttOneListener= new ButtoneListener();// 生成监听对象 
    button.setOnClickListener(buttoneListener);// 按钮绑定一个监听器 
  } 
 
  @Override 
  public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
  } 
 
  class ButtoneListener implements OnClickListener// 创建一个类实现监听事件的接口 
  { 
 
    @Override 
    public void onClick(View arg0) { 
      // TODO Auto-generated method stub 
      count++; 
      textView.setText(Integer.toString(count)); 
 
    } 
 
  } 
 
} 

package com.androidclub.elfman.homework3; 
import java.util.ArrayList; 
import java.util.Random; 
import android.app.Activity; 
import android.content.Context; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.graphics.Paint.Style; 
import android.os.Bundle; 
import android.view.View; 
public class Main extends Activity { 
  TheScreen mScreen; 
  @Override 
  public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    //mScreen是自定义的View 
    mScreen = new TheScreen(this); 
    setContentView(mScreen); 
  } 
   
  //为避免在程序退出后线程仍在进行,造成不必要的系统资源浪费,在Activity退出是时候,主动将线程停止 
  @Override 
  public void onDestroy() 
  { 
    mScreen.stopDrawing(); 
    super.onDestroy(); 
  } 
} 
/** 
 * 自定义的View类,为两个球的碰撞模拟 
 * @author windy 
 * 
 */ 
class TheScreen extends View 
{ 
   
  private static final String TAG = "Draw"; 
  //界面主线程的控制变量 
  private boolean drawing = false; 
  //储存当前已有的球的信息 
  private ArrayList circles; 
  private Paint mPaint; 
  //两个球的运动范围 
  public static final int WIDTH = 300; 
  public static final int HEIGHT = 400; 
  public static final double PI = 3.14159265; 
  Paint mPaint2 = new Paint(); 
  public TheScreen(Context context) 
  { 
    super(context); 
    circles = new ArrayList(); 
    //加入了两个球 
    circles.add(new Circle()); 
    circles.add(new Circle(20, 30, 10)); 
    mPaint = new Paint(); 
    mPaint.setColor(Color.YELLOW); 
    mPaint.setAntiAlias(true); 
    mPaint2.setStyle(Style.STROKE); 
    mPaint2.setColor(Color.RED); 
    mPaint2.setAntiAlias(true); 
    //启动界面线程,开始自动更新界面 
    drawing = true; 
    new Thread(mRunnable).start(); 
  } 
   
  private Runnable mRunnable = new Runnable() { 
    //界面的主线程 
    @Override 
    public void run() { 
      while( drawing ) 
      { 
        try { 
          //更新球的位置信息 
          update(); 
          //通知系统更新界面,相当于调用了onDraw函数 
          postInvalidate(); 
          //界面更新的频率,这里是每30ms更新一次界面 
          Thread.sleep(30); 
          //Log.e(TAG, "drawing"); 
        } catch (InterruptedException e) { 
          e.printStackTrace(); 
        } 
      } 
    } 
  }; 
   
  public void stopDrawing() 
  { 
    drawing = false; 
  } 
   
   
  @Override 
  public void onDraw(Canvas canvas) 
  { 
    //在canvas上绘上边框 
    canvas.drawRect(0, 0, WIDTH, HEIGHT, mPaint2); 
    //在canvas上绘上球 
    for( Circle circle : circles) 
    { 
      canvas.drawCircle(circle.x, circle.y, circle.radius, mPaint); 
    } 
  } 
   
  //界面的逻辑函数,主要检查球是否发生碰撞,以及更新球的位置 
  private void update() 
  { 
    if( circles.size()>1) 
    { 
      for( int i1=0; i1=WIDTH ) 
      { 
        if( angle >=0 && angle <= (PI/2)) 
          angle = PI - angle; 
        if( angle > 1.5 * PI && angle <= 2*PI) 
          angle = 3 * PI - angle;        
      } 
      if( x-radius <=0 ) 
      { 
        if( angle >= PI && angle <= 1.5*PI ) 
          angle = 3*PI - angle; 
        if( angle >= PI/2 && angle =HEIGHT) 
        angle = 2*PI - angle; 
       
    } 
    //两球交换角度 
    public void changeDerection(Circle other) 
    { 
      double temp = this.angle; 
      this.angle = other.angle; 
      other.angle = temp; 
    } 
  } 
}