Android自定義元件及屬性

下面的例子說明了如何使用自定義屬性，並定義一個簡單Android的自定義元件。

下面是修改後的主活動檔案 src/com.yiibai.dateviewdemo/MainActivity.java 的內容。該檔案可以包含每一個生命週期的基本方法。

package com.example.dateviewdemo;

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

public class MainActivity extends Activity {

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

    @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;
    }
    
}

下面是 res/values/attrs.xml 檔案的內容：

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <declare-styleable name="DateView">
   <attr name="delimiter" format="string"/>
   <attr name="fancyText" format="boolean"/>
   </declare-styleable>
</resources>

以下將是新的檔案 src/com.yiibai.dateviewdemo/DateView.java 的內容，有的附加功能以顯示當前日期：

package com.example.dateviewdemo;

import java.text.SimpleDateFormat;
import java.util.Calendar;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Color;
import android.util.AttributeSet;
import android.util.Log;
import android.widget.TextView;

public class DateView extends TextView {
   public String delimiter;
   public boolean fancyText;

   public DateView(Context context) {
      super(context);
      setDate();
   }

   public DateView(Context context, AttributeSet attrs) {
      super(context, attrs);
      TypedArray a = context.obtainStyledAttributes(attrs, 
      R.styleable.DateView );
      final int N = a.getIndexCount();
      for (int i = 0; i < N; ++i)
      {
         int attr = a.getIndex(i);

         switch (attr)
         {
            case R.styleable.DateView_delimiter:
            delimiter = a.getString(attr);
            setDate();
            break;
         case R.styleable.DateView_fancyText:
            fancyText = a.getBoolean(attr, false);
            fancyText();
            break;
         }
      }
      a.recycle();
   }

   public DateView(Context context, AttributeSet attrs, int defStyle) {
      super(context, attrs, defStyle);
      setDate();
   }

   private void setDate() {
      SimpleDateFormat dateFormat = 
      new SimpleDateFormat("yyyy" + delimiter + "MM" + delimiter + "dd");
      String today = dateFormat.format(Calendar.getInstance().getTime());
      setText(today);  // self = DateView = subclass of TextView
   }

   private void fancyText() {
      if( this.fancyText){
         setShadowLayer(9, 1, 1, Color.rgb(44, 44, 40));
      }
   }
}

下面是 res/layout/activity_main.xml 檔案的內容：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:custom="http://schemas.android.com/apk/res/com.yiibai.dateviewdemo"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >
    
    <com.yiibai.dateviewdemo.DateView
    android:layout_width="match_parent"
    android:layout_height="wrap_content" 
    android:textColor="#fff"
    android:textSize="40sp"
    custom:delimiter="-"
    custom:fancyText="true"
    />

</RelativeLayout>

以下將是 res/values/strings.xml  中定義兩個新常數的內容：

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">DateViewDemo</string>
    <string name="action_settings">Settings</string>
    <string name="hello_world">Hello world!</string>
   
</resources>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.yiibai.guidemo"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.yiibai.guidemo.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>