Android自定义控件(二)：继承原生控件

继承原生控件,对其功能适当扩展，以适应需求。如下实例：

下面以一个不允许输入表情的EditText作为例子 

@SuppressLint("AppCompatCustomView")
public class EmoEditText extends EditText {
    //输入表情前的光标位置
    private int cursorPos;
    //输入表情前EditText中的文本
    private String inputAfterText;
    //是否重置了EditText的内容
    private boolean resetText;
 
    private Context mContext;
 
    public EmoEditText(Context context) {
        super(context);
        this.mContext = context;
        initEditText();
    }
 
    public EmoEditText(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.mContext = context;
        initEditText();
    }
 
    public EmoEditText(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.mContext = context;
        initEditText();
    }
 
    // 初始化edittext 控件
    private void initEditText() {
        addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int before, int count) {
                if (!resetText) {
                    cursorPos = getSelectionEnd();
                    // 这里用s.toString()而不直接用s是因为如果用s，
                    // 那么，inputAfterText和s在内存中指向的是同一个地址，s改变了，
                    // inputAfterText也就改变了，那么表情过滤就失败了
                    inputAfterText= s.toString();
                }
            }
 
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                if (!resetText) {
                    if (count >= 2) {//表情符号的字符长度最小为2
                        CharSequence input = s.subSequence(cursorPos, cursorPos + count);
                        if (containsEmoji(input.toString())) {
                            resetText = true;
                            Toast.makeText(mContext, "暂不支持表情评论哦", Toast.LENGTH_SHORT).show();
                            //是表情符号就将文本还原为输入表情符号之前的内容
                            setText(inputAfterText);
                            CharSequence text = getText();
                            if (text instanceof Spannable) {
                                Spannable spanText = (Spannable) text;
                                Selection.setSelection(spanText, text.length());
                            }
                        }
                    }
                } else {
                    resetText = false;
                }
            }
 
            @Override
            public void afterTextChanged(Editable editable) {
 
            }
        });
    } 
 
    /**
     * 检测是否有emoji表情
     *
     * @param source
     * @return
     */
    public static boolean containsEmoji(String source) {
        int len = source.length();
        for (int i = 0; i < len; i++) {
            char codePoint = source.charAt(i);
            if (!isEmojiCharacter(codePoint)) { //如果不能匹配,则该字符是Emoji表情
                return true;
            }
        }
        return false;
    }
 
    /**
     * 判断是否是Emoji
     *
     * @param codePoint 比较的单个字符
     * @return
     */
    private static boolean isEmojiCharacter(char codePoint) {
        return (codePoint == 0x0) || (codePoint == 0x9) || (codePoint == 0xA) ||
                (codePoint == 0xD) || ((codePoint >= 0x20) && (codePoint <= 0xD7FF)) ||
                ((codePoint >= 0xE000) && (codePoint <= 0xFFFD)) || ((codePoint >= 0x10000)
                && (codePoint <= 0x10FFFF));
    }
}

然后在activity_main.xml引入该控件就可以了 

<com.example.EmoEditText
    android:id="@+id/edtext"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />