不廢話，直接上程式碼，都是基礎，基本能看的懂,直接複製貼上即可使用；

介面佈局：

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="100dp"
                android:layout_marginRight="20dp"
                android:background="@drawable/edit_bt"
                android:orientation="vertical"
                android:paddingTop="5dp">


                <EditText
                    android:id="@+id/ed_cooperation_introduce"
                    style="@style/help_layout"
                    android:layout_width="match_parent"
                    android:layout_height="80dp"
                    android:background="@null"
                    android:gravity="left|top"
                    android:hint="請用文字簡單描述您的合作內容（100字內）"
                    android:padding="5dp"
                    android:textSize="12sp" />

                <TextView
                    android:id="@+id/tv_cooperation_hin"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:gravity="right"
                    android:paddingRight="5dp"
                    android:text="100"
                    android:textSize="12sp" />

            </LinearLayout>
 

oncreate程式碼；

  //顯示輸入字元數量
        showCharNumber(100);
        //判斷etContent.gettext()是否為空
        if (TextUtils.isEmpty(binding.edCooperationIntroduce.getText().toString())) {
            binding.tvCooperationHin.setText("100");
        } else {
            int ed_lenght = binding.edCooperationIntroduce.getText().length();
            int lenght = 100 - ed_lenght;
            binding.tvCooperationHin.setText(String.valueOf(lenght));
        }


 

  private void showCharNumber(final int maxNumber) {
        binding.edCooperationIntroduce.addTextChangedListener(new TextWatcher() {
            private CharSequence temp;
            private int selectionStart;
            private int selectionEnd;

            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                temp = s;
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {
                int number = s.length();
                int lenght = 100 - number;
//                tv_size.setText(number + "/" + maxNumber);
                binding.tvCooperationHin.setText(String.valueOf(lenght));
                selectionStart = binding.edCooperationIntroduce.getSelectionStart();
                selectionEnd = binding.edCooperationIntroduce.getSelectionEnd();
                //System.out.println("start="+selectionStart+",end="+selectionEnd);
                if (temp.length() > maxNumber) {
                    s.delete(selectionStart - 1, selectionEnd);
                    int tempSelection = selectionStart;
                    binding.edCooperationIntroduce.setText(s);
                    binding.edCooperationIntroduce.setSelection(tempSelection);
                    toast("最多100字");
                }
            }
        });
    }