Android字符串格式化开源库phrase介绍

Android字符串格式化开源库phrase介绍

在上一篇博客Android通过String.format格式化（动态改变）字符串资源的显示内容中介绍了通过String.format来格式化string.xml文件中的字符串，本文介绍一个可以实现同样功能的开源库phrase，相比于String.format，通过phrase格式化字符串代码更具可读性。

一、phrase项目介绍：

1、源码：phrase项目的源代码很简单，里面总共只有一个类：Phrase.java，代码如下：

/*
 * Copyright (C) 2013 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.uperone.stringformat;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import android.app.Fragment;
import android.content.Context;
import android.content.res.Resources;
import android.text.SpannableStringBuilder;
import android.view.View;

/**
 * A fluent API for formatting Strings. Canonical usage:
 * <pre class="code">
 *   CharSequence formatted = Phrase.from("Hi {first_name}, you are {age} years old.")
 *       .put("first_name", firstName)
 *       .put("age", age)
 *       .format();
 * 

*

*
• Surround keys with curly braces; use two {{ to escape.
*
• Keys start with lowercase letters followed by lowercase letters and underscores.
*
• Spans are preserved, such as simple HTML tags found in strings.xml.
*
• Fails fast on any mismatched keys.
*

* The constructor parses the original pattern into a doubly-linked list of {@link Token}s. * These tokens do not modify the original pattern, thus preserving any spans. *

* The {@link #format()} method iterates over the tokens, replacing text as it iterates. The * doubly-linked list allows each token to ask its predecessor for the expanded length. */ public final class Phrase { /** The unmodified original pattern. */ private final CharSequence pattern; /** All keys parsed from the original pattern, sans braces. */ private final Set keys = new HashSet(); private final Map keysToValues = new HashMap(); /** Cached result after replacing all keys with corresponding values. */ private CharSequence formatted; /** The constructor parses the original pattern into this doubly-linked list of tokens. */ private Token head; /** When parsing, this is the current character. */ private char curChar; private int curCharIndex; /** Indicates parsing is complete. */ private static final int EOF = 0; /** * Entry point into this API. * * @throws IllegalArgumentException if pattern contains any syntax errors. */ public static Phrase from(Fragment f, int patternResourceId) { return from(f.getResources(), patternResourceId); } /** * Entry point into this API. * * @throws IllegalArgumentException if pattern contains any syntax errors. */ public static Phrase from(View v, int patternResourceId) { return from(v.getResources(), patternResourceId); } /** * Entry point into this API. * * @throws IllegalArgumentException if pattern contains any syntax errors. */ public static Phrase from(Context c, int patternResourceId) { return from(c.getResources(), patternResourceId); } /** * Entry point into this API. * * @throws IllegalArgumentException if pattern contains any syntax errors. */ public static Phrase from(Resources r, int patternResourceId) { return from(r.getText(patternResourceId)); } /** * Entry point into this API; pattern must be non-null. * * @throws IllegalArgumentException if pattern contains any syntax errors. */ public static Phrase from(CharSequence pattern) { return new Phrase(pattern); } /** * Replaces the given key with a non-null value. You may reuse Phrase instances and replace * keys with new values. * * @throws IllegalArgumentException if the key is not in the pattern. */ public Phrase put(String key, CharSequence value) { if (!keys.contains(key)) { throw new IllegalArgumentException("Invalid key: " + key); } if (value == null) { throw new IllegalArgumentException("Null value for '" + key + "'"); } keysToValues.put(key, value); // Invalidate the cached formatted text. formatted = null; return this; } /** @see #put(String, CharSequence) */ public Phrase put(String key, int value) { if (!keys.contains(key)) { throw new IllegalArgumentException("Invalid key: " + key); } keysToValues.put(key, Integer.toString(value)); // Invalidate the cached formatted text. formatted = null; return this; } /** * Silently ignored if the key is not in the pattern. * * @see #put(String, CharSequence) */ public Phrase putOptional(String key, CharSequence value) { return keys.contains(key) ? put(key, value) : this; } /** @see #put(String, CharSequence) */ public Phrase putOptional(String key, int value) { return keys.contains(key) ? put(key, value) : this; } /** * Returns the text after replacing all keys with values. * * @throws IllegalArgumentException if any keys are not replaced. */ public CharSequence format() { if (formatted == null) { if (!keysToValues.keySet().containsAll(keys)) { Set missingKeys = new HashSet(keys); missingKeys.removeAll(keysToValues.keySet()); throw new IllegalArgumentException("Missing keys: " + missingKeys); } // Copy the original pattern to preserve all spans, such as bold, italic, etc. SpannableStringBuilder sb = new SpannableStringBuilder(pattern); for (Token t = head; t != null; t = t.next) { t.expand(sb, keysToValues); } formatted = sb; } return formatted; } /** * Returns the raw pattern without expanding keys; only useful for debugging. Does not pass * through to {@link #format()} because doing so would drop all spans. */ @Override public String toString() { return pattern.toString(); } private Phrase(CharSequence pattern) { curChar = (pattern.length() > 0) ? pattern.charAt(0) : EOF; this.pattern = pattern; // A hand-coded lexer based on the idioms in "Building Recognizers By Hand". // http://www.antlr2.org/book/byhand.pdf. Token prev = null; Token next; while ((next = token(prev)) != null) { // Creates a doubly-linked list of tokens starting with head. if (head == null) head = next; prev = next; } } /** Returns the next token from the input pattern, or null when finished parsing. */ private Token token(Token prev) { if (curChar == EOF) { return null; } if (curChar == '{') { char nextChar = lookahead(); if (nextChar == '{') { return leftCurlyBracket(prev); } else if (nextChar >= 'a' && nextChar = 'a' && curChar data); /** Returns the number of characters after expansion. */ abstract int getFormattedLength(); /** Returns the character index after expansion. */ final int getFormattedStart() { if (prev == null) { // The first token. return 0; } else { // Recursively ask the predecessor node for the starting index. return prev.getFormattedStart() + prev.getFormattedLength(); } } } /** Ordinary text between tokens. */ private static class TextToken extends Token { private final int textLength; TextToken(Token prev, int textLength) { super(prev); this.textLength = textLength; } @Override void expand(SpannableStringBuilder target, Map data) { // Don't alter spans in the target. } @Override int getFormattedLength() { return textLength; } } /** A sequence of two curly brackets. */ private static class LeftCurlyBracketToken extends Token { LeftCurlyBracketToken(Token prev) { super(prev); } @Override void expand(SpannableStringBuilder target, Map data) { int start = getFormattedStart(); target.replace(start, start + 2, "{"); } @Override int getFormattedLength() { // Replace {{ with {. return 1; } } private static class KeyToken extends Token { /** The key without { and }. */ private final String key; private CharSequence value; KeyToken(Token prev, String key) { super(prev); this.key = key; } @Override void expand(SpannableStringBuilder target, Map data) { value = data.get(key); int replaceFrom = getFormattedStart(); // Add 2 to account for the opening and closing brackets. int replaceTo = replaceFrom + key.length() + 2; target.replace(replaceFrom, replaceTo, value); } @Override int getFormattedLength() { // Note that value is only present after expand. Don't error check because this is all // private code. return value.length(); } } }

2、字符串格式化原理：

通过阅读Phrase.java的代码可知，它用"{"和"}"将需要格式化的内容包起来，然后用键值对给需要改变的内容传值，包起来的内容为键，值为动态设置的内容，比如：

"Hi {first_name}, you are {age} years old."

我们要最终的显示内容为：“Hi UperOne, you are 26 years old.”这里的first_name和age是键，值为UperOne和26。

二、使用方法：

Phrase.java的类名上面的注释已经告诉了我们具体的使用方法：

/**
 * A fluent API for formatting Strings. Canonical usage:
 * 
 *   CharSequence formatted = Phrase.from("Hi {first_name}, you are {age} years old.")
 *       .put("first_name", firstName)
 *       .put("age", age)
 *       .format();
 * 
 * 

 * 
Surround keys with curly braces; use two {{ to escape.
 * 
Keys start with lowercase letters followed by lowercase letters and underscores.
 * 
Spans are preserved, such as simple HTML tags found in strings.xml.
 * 
Fails fast on any mismatched keys.
 * 
 * The constructor parses the original pattern into a doubly-linked list of {@link Token}s.
 * These tokens do not modify the original pattern, thus preserving any spans.
 * 

 * The {@link #format()} method iterates over the tokens, replacing text as it iterates. The
 * doubly-linked list allows each token to ask its predecessor for the expanded length.
 */
public final class Phrase

比如：


CharSequence parseStr = Phrase.from("Hi {first_name}, you are {age} years old.")
				 .put("first_name", "UperOne")
				 .put("age", "26")
				 .format();
		
mParseTxt.setText( parseStr );
用起来非常简单。