自定义组件(DrawView) 提高代码复用性

编写DrawView的代码：

package com.example.drawview;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class DrawView extends View {

Paint paint = null;
float startX = 0;//用来缓冲起始位置x
float startY = 0;//用来缓冲起始位置y
float stopX = 0;
float stopY = 0;

Bitmap cache = null;
private Canvas cacheCanvas;
private Matrix matrix;
/*
* XML 生成一个View对象的时候会被调用。且有样式设置的时候调用这个构造函数
*/
public DrawView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}

/**
* xml生成View且没有设置样式主题的时候会被调用
*/
public DrawView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}

/**
* 通过代码创建的时候会被调用
*/
public DrawView(Context context) {
super(context);
init();
}

//定义一个初始化的方法
private void init()
{
paint = new Paint();
matrix = new Matrix();
}

/**
*/
@Override
protected void onDraw(Canvas canvas) {

if(cache == null)
{
cache = Bitmap.createBitmap(getWidth(), getHeight(), Config.ARGB_8888);
cacheCanvas = new Canvas(cache);
//这个方法会把view要显示的内容绘制到界面上
cacheCanvas.drawColor(0xffaaaaaa);
}

cacheCanvas.drawLine(startX, startY, stopX, stopY, paint);
startX = stopX;
startY = stopY;

canvas.drawBitmap(cache, matrix, paint);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
startX = event.getX();
startY = event.getY();
break;

case MotionEvent.ACTION_MOVE:
stopX = event.getX();
stopY = event.getY();
invalidate();//通知界面绘制内容
break;
case MotionEvent.ACTION_UP:
break;
default:
break;
}
return true;
}

}


编写ScondActivity代码：(调用DrawView中的代码)

package com.example.drawview;

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

public class ScondActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

DrawView view = new DrawView(this);//调用DrawView类，直接使用，提高代码复用性
this.setContentView(view);
}
}

最后在MainActivity中调用，使之回调到主Activity上：

package com.example.drawview;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.RelativeLayout;
import android.widget.RelativeLayout.LayoutParams;
import android.widget.TextView;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}

public void skip(View view)
{
Intent intent = new Intent(this, ScondActivity.class);
startActivity(intent);
}
}


降低各个组件之间的偶合度，提高代码复用性！！！(类似Java EE中的MVC设计模式)