使用TextWatcher監聽EditText變化

public class MainActivity extends AppCompatActivity {
    private TextView mTextView;
    private EditText mEditText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mTextView = (TextView) findViewById(R.id.tv);
        mEditText = (EditText) findViewById(R.id.et);
        /**
         * 監聽EditText框中的變化
         */
        mEditText.addTextChangedListener(new TextWatcher() {
            private CharSequence temp;
            private int editStart;
            private int editEnd;

            /**
             * 文本變化之前
             * @param s
             * @param start
             * @param count
             * @param after
             */
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                temp = s;
            }

            /**
             * 文本變化中
             * @param s
             * @param start
             * @param before
             * @param count
             */
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                mTextView.setText("輸入的結果為:"+s);
            }

            /**
             * 文本變化之后
             * @param s
             */
            @Override
            public void afterTextChanged(Editable s) {
                editStart = mEditText.getSelectionStart();
                editEnd = mEditText.getSelectionEnd();
                if (temp.length() > 10) {//限制長度
                    Toast.makeText(MainActivity.this,
                            "輸入的字數已經超過了限制！", Toast.LENGTH_SHORT)
                            .show();
                    s.delete(editStart - 1, editEnd);
                    int tempSelection = editStart;
                    mEditText.setText(s);
                    mEditText.setSelection(tempSelection);
                }

            }
        });

    }
}

結果：