基于Tweet长度的java文本过滤

Question

我试图找出如何将编辑文本字段限制为140个twitter字符，而不允许用户键入超过限制的内容。我想我已经使用了下面的代码，但是，我发现只有当光标位于editText字段的末尾时，它才能阻止键入。尽管我已经尝试了很多，但我无法理解source和dest的逻辑，以及如何将它们连接到editText字段中显示的完整字符串中。这就是我试图对fullTextString执行的操作

注意，这并不像限制编辑文本字段的长度那么简单。Twitter认为像“t.co”这样的链接是22个字符，而不是3个。我没有看到任何其他有效的例子

github上有一个快速克隆的完整示例： https://github.com/tylerjroach/TwitterEditTextLengthFilter

public class TwitterLengthFilter implements InputFilter {
Validator tweetValidator = new Validator();
private final int max;

public TwitterLengthFilter(int max) {
    this.max = max;
}

public CharSequence filter(CharSequence source, int start, int end, Spanned dest,
                           int dstart, int dend) {

    String destString = dest.subSequence(0, dstart).toString();
    String sourceString = source.subSequence(start, end).toString();
    String fullTextString = destString + sourceString;

    if (fullTextString.length() == 0) {
        return "";
    } else if (tweetValidator.getTweetLength(fullTextString) <= max) {
        return null; //keep original
    } else {
        CharSequence returnSource = "";
        for (int i=0; i<sourceString.length(); i++) {
            if (tweetValidator.getTweetLength(destString + source.subSequence(0, i + 1)) <= max) {
                returnSource = source.subSequence(0, i + 1);
            }
        }
        return returnSource;
    }
}

}

Answer 1

尝试将其添加到编辑文本XML中：

android:maxLength="140"

Answer 2

在阅读了更多关于过滤方法的内容后，我终于能够理解它。我相信它会更有效率，但目前它还有效。我希望有任何建议能让它变得更好

This method is called when the buffer is going to replace the range dstart … dend of dest with the new text from the range start … end of source. Return the CharSequence that you would like to have placed there instead, including an empty string if appropriate, or null to accept the original replacement. Be careful to not to reject 0-length replacements, as this is what happens when you delete text. Also beware that you should not attempt to make any changes to dest from this method; you may only examine it for context. Note: If source is an instance of Spanned or Spannable, the span objects in the source should be copied into the filtered result (i.e. the non-null return value). copySpansFrom(Spanned, int, int, Class, Spannable, int) can be used for convenience.

public class TwitterLengthFilter implements InputFilter {
Validator tweetValidator = new Validator();
private final int max;

public TwitterLengthFilter(int max) {
    this.max = max;
}

public CharSequence filter(CharSequence source, int start, int end, Spanned dest,
                           int dstart, int dend) {

    StringBuilder destination = new StringBuilder(dest);
    String sourceString = source.subSequence(start, end).toString();
    String fullTextString = destination.replace(dstart, dend, sourceString).toString();

    Log.v("Full text", fullTextString);

    if (fullTextString.length() == 0) {
        return "";
    } else if (tweetValidator.getTweetLength(fullTextString) <= max) {
        return null; //keep original
    } else {
        CharSequence returnSource = "";
        for (int i=0; i<sourceString.length(); i++) {
            String iterateSource = source.subSequence(0, i + 1).toString();
            StringBuilder iteratedDestination = new StringBuilder(dest);
            iteratedDestination.replace(dstart, dend, iterateSource);
            if (tweetValidator.getTweetLength(iteratedDestination.toString()) <= max) {
                returnSource = source.subSequence(0, i + 1);
            }
        }
        return returnSource;
    }
}