Android高手进阶教程(四)之----Android 中自定义属性(attr.xml,TypedArray)的使用!

今天我们的教程是根据前面一节扩展进行的，如果你没有看,请点击 Android高手进阶教程(三)查看第三课,这样跟容易方便你的理解!

在xml文件里定义控件的属性，我们已经习惯了android:attrs="",那么我们能不能定义自己的属性能，比如:test:attrs=""呢？答案是肯定的.

好了我就不卖关子了，直接进入主题。大致以下步骤:

一、在res/values文件下定义一个attrs.xml文件.代码如下:

一、在res/values文件下定义一个attrs.xml文件.代码如下:
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="MyView">
        <attr name="textColor" format="color" />
        <attr name="textSize" format="dimension" />
    </declare-styleable>
</resources>

一、在res/values文件下定义一个attrs.xml文件.代码如下: <?xml version="1.0" encoding="utf-8"?> <resources> <declare-styleable name="MyView"> <attr name="textColor" format="color" /> <attr name="textSize" format="dimension" /> </declare-styleable> </resources>

二、我们在MyView.java代码修改如下，其中下面的构造方法是重点，我们获取定义的属性我们R.sytleable.MyView_textColor,获取方法中后面通常设定默认值(float textSize = a.getDimension(R.styleable.MyView_textSize, 36);)，防止我们在xml文件中没有定义.从而使用默认值!

获取，MyView就是定义在<declare-styleable name="MyView"></declare-styleable>里的 名字,获取里面属性用 名字_ 属性连接起来就可以.TypedArray通常最后调用 .recycle()方法，为了保持以后使用该属性一致性！

public MyView(Context context,AttributeSet attrs)
    {
        super(context,attrs);
        mPaint = new Paint();

        TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.MyView);

        int textColor = a.getColor(R.styleable.MyView_textColor,
                0XFFFFFFFF);
        float textSize = a.getDimension(R.styleable.MyView_textSize, 36);

        mPaint.setTextSize(textSize);
        mPaint.setColor(textColor);

        a.recycle();
    }

public MyView(Context context,AttributeSet attrs) { super(context,attrs); mPaint = new Paint(); TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MyView); int textColor = a.getColor(R.styleable.MyView_textColor, 0XFFFFFFFF); float textSize = a.getDimension(R.styleable.MyView_textSize, 36); mPaint.setTextSize(textSize); mPaint.setColor(textColor); a.recycle(); }

MyView.java全部代码如下:

package com.android.tutor;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.Paint.Style;
import android.util.AttributeSet;
import android.view.View;
public class MyView extends View {
    private Paint mPaint;
    private Context mContext;
    private static final String mString = "Welcome to Mr Wei's blog";

    public MyView(Context context) {
        super(context);
        mPaint = new Paint();
    }
    public MyView(Context context,AttributeSet attrs)
    {
        super(context,attrs);
        mPaint = new Paint();

        TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.MyView);

        int textColor = a.getColor(R.styleable.MyView_textColor,
                0XFFFFFFFF);
        float textSize = a.getDimension(R.styleable.MyView_textSize, 36);

        mPaint.setTextSize(textSize);
        mPaint.setColor(textColor);

        a.recycle();
    }
    @Override
    protected void onDraw(Canvas canvas) {
        // TODO Auto-generated method stub
        super.onDraw(canvas);
        //设置填充
        mPaint.setStyle(Style.FILL);

        //画一个矩形,前俩个是矩形左上角坐标，后面俩个是右下角坐标
        canvas.drawRect(new Rect(10, 10, 100, 100), mPaint);

        mPaint.setColor(Color.BLUE);
        //绘制文字
        canvas.drawText(mString, 10, 110, mPaint);
    }
}

package com.android.tutor; import android.content.Context; import android.content.res.TypedArray; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Rect; import android.graphics.Paint.Style; import android.util.AttributeSet; import android.view.View; public class MyView extends View { private Paint mPaint; private Context mContext; private static final String mString = "Welcome to Mr Wei's blog"; public MyView(Context context) { super(context); mPaint = new Paint(); } public MyView(Context context,AttributeSet attrs) { super(context,attrs); mPaint = new Paint(); TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MyView); int textColor = a.getColor(R.styleable.MyView_textColor, 0XFFFFFFFF); float textSize = a.getDimension(R.styleable.MyView_textSize, 36); mPaint.setTextSize(textSize); mPaint.setColor(textColor); a.recycle(); } @Override protected void onDraw(Canvas canvas) { // TODO Auto-generated method stub super.onDraw(canvas); //设置填充 mPaint.setStyle(Style.FILL); //画一个矩形,前俩个是矩形左上角坐标，后面俩个是右下角坐标 canvas.drawRect(new Rect(10, 10, 100, 100), mPaint); mPaint.setColor(Color.BLUE); //绘制文字 canvas.drawText(mString, 10, 110, mPaint); } }

三、将我们自定义的MyView加入布局main.xml文件中，平且使用自定义属性,自定义属性必须加上:

      xmlns:test="http://schemas.android.com/apk/res/com.android.tutor"蓝色是自定义属性的前缀，红色是我们包名.

main.xml全部代码如下:

<?xml
version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:test="http://schemas.android.com/apk/res/com.android.tutor"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello"
    />
<com.android.tutor.MyView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    test:textSize="20px"
    test:textColor="#fff"
/>
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:test="http://schemas.android.com/apk/res/com.android.tutor" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> <com.android.tutor.MyView android:layout_width="fill_parent" android:layout_height="fill_parent" test:textSize="20px" test:textColor="#fff" /> </LinearLayout>