建立自定義視圖(Custom View)

在Android, 你可以擴展視圖類(View), 從而建立自定義的視圖類.



- 首先, 擴展View定義新類:
public class MyView extends View

- 重寫構造函數:
public MyView(Context context)
public MyView(Context context, AttributeSet attrs)
public MyView(Context context, AttributeSet attrs, int defStyle)

- 重寫protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
必須重寫此方法, 調用setMeasuredDimension(int, int)方法設定measuredWith和measuredHeight.

簡單起見, 本例子只使用下面的代碼設定measuredWith和measuredHeight:
setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec), MeasureSpec.getSize(heightMeasureSpec));

- 重寫protected void onDraw(Canvas canvas)
這裡是你實際繪製你的視圖的代碼.

- 在public void onCreate(Bundle savedInstanceState)設置使用你的自定義視圖.
MyView myView = new MyView(this);
setContentView(myView);

MyView.java

package com.AndroidView;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class MyView extends View {
 
 private Paint myPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

 public MyView(Context context) {
  super(context);
  // TODO Auto-generated constructor stub
 }

 public MyView(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub
 }

 public MyView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  // TODO Auto-generated constructor stub
 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  // TODO Auto-generated method stub
  //super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  
  setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec),
    MeasureSpec.getSize(heightMeasureSpec));
 }

 @Override
 protected void onDraw(Canvas canvas) {
  // TODO Auto-generated method stub
  //super.onDraw(canvas);
  
  int radius;
  int height = getMeasuredHeight();
  int width = getMeasuredWidth();
  int centerX = width/2;
  int centerY = height/2;
  
  if (height>width){
   radius = width/2;
  }
  else{
   radius = height/2;
  }
  
  myPaint.setStyle(Paint.Style.STROKE);
  myPaint.setColor(Color.WHITE);
  
  myPaint.setStrokeWidth(1);
  canvas.drawLine(centerX, centerY-10, centerX, centerY+10, myPaint);
  canvas.drawLine(centerX-10, centerY, centerX+10, centerY, myPaint);
  
  myPaint.setStrokeWidth(10);
  myPaint.setColor(Color.RED);
  canvas.drawRect(0, 0, width, height, myPaint);
  
  myPaint.setStrokeWidth(3);
  myPaint.setColor(Color.GREEN);
  
  
  canvas.drawCircle(centerX, centerY, radius, myPaint);
 }

}

AndroidView.java

package com.AndroidView;

import android.app.Activity;
import android.os.Bundle;

public class AndroidView extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       //setContentView(R.layout.main);
      
       MyView myView = new MyView(this);
       setContentView(myView);
   }
}

next: 通過XML調用自定義視圖(Custom View)