自定义xml属性attr

xmlns:android是XML命名空间，告诉Android开发工具你准备使用Android命名空间里的一些通用属性

在所有Android XML文件中最外层的标记必须使用这个命名空间

用户也可以自定义XML属性

1. values/attrs.xml定义属性

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <attr name="relative">
        <enum name="icon_left" value="0" />
        <enum name="icon_right" value="1" />
        <enum name="icon_above" value="2" />
        <enum name="icon_below" value="3" />
    </attr>

    <declare-styleable name="IconTextView">
        <attr name="relative"/>
        <attr name="my_icon" format="reference"/>
        <attr name="my_text" format="string"/>
        <attr name="text_size" format="dimension"/>
        <attr name="text_color" format="color"/>
        <attr name="padding" format="dimension"/>
    </declare-styleable>
</resources>

2. IconTextView.java继承LinearLayout实现自定义的属性

package com.silion.userdefinedxmlattr;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.drawable.Drawable;
import android.media.Image;
import android.util.AttributeSet;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

/**
 * Created by silion on 2015/10/19.
 */
public class IconTextView extends LinearLayout {
    private final static int ICON_LEFT = 0;
    private final static int ICON_RIGHT = 1;
    private final static int ICON_ABOVE = 2;
    private final static int ICON_BELOW = 3;

    private int mRelative;
    private Drawable mIcon;
    private String mText;
    private float mTextSize;
    private Integer mTextColor;
    private int mPadding;
    private TextView mTextView;
    private ImageView mImageView;

    public IconTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = null;
        try {
            a = context.obtainStyledAttributes(attrs, R.styleable.IconTextView);
            mRelative = a.getInt(R.styleable.IconTextView_relative, 0);
            mIcon = a.getDrawable(R.styleable.IconTextView_my_icon);
            mText = a.getString(R.styleable.IconTextView_my_text);
            mTextSize = a.getDimension(R.styleable.IconTextView_text_size, 15);
            mTextColor = a.getInteger(R.styleable.IconTextView_text_color, 0);
            mPadding = a.getInt(R.styleable.IconTextView_padding, 15);
        } finally {
            a.recycle();
        }

        mTextView = new TextView(context);
        mTextView.setText(mText);
        mTextView.setTextSize(mTextSize);
        mTextView.setTextColor(mTextColor);

        mImageView = new ImageView(context);
        mImageView.setImageDrawable(mIcon);

        int paddingLeft = 0;
        int paddingRight = 0;
        int paddingTop = 0;
        int paddingBottom = 0;
        int orientation = HORIZONTAL;
        switch (mRelative) {
            case ICON_LEFT: {
                orientation = HORIZONTAL;
                paddingLeft = mPadding;
                break;
            }
            case ICON_RIGHT: {
                orientation = HORIZONTAL;
                paddingRight = mPadding;
                break;
            }
            case ICON_ABOVE: {
                orientation = VERTICAL;
                paddingTop = mPadding;
                break;
            }
            case ICON_BELOW: {
                orientation = VERTICAL;
                paddingBottom = mPadding;
                break;
            }
            default:
                break;
        }
        this.setOrientation(orientation);
        mImageView.setPadding(paddingLeft, paddingTop, paddingRight, paddingBottom);
        this.addView(mImageView);
        this.addView(mTextView);
    }
}

3. 在layout/activity_main.xml中定义xmlns使用自定义的属性

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <com.silion.userdefinedxmlattr.IconTextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:relative="icon_right"
        app:my_icon="@mipmap/ic_launcher"
        app:my_text="@string/hello_world"
        app:text_size="19sp"
        app:text_color="#0000ff"
        android:padding="16dp"/>
</LinearLayout>

4.MainActivity.java

package com.silion.userdefinedxmlattr;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;


public class MainActivity extends ActionBarActivity {

    @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.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}