好長時間沒有上知乎了，今天開啟的時候，發現提示令牌失效了，讓重新登陸，一看這個效果，其實很好實現的，在Material Design裡面其實有相關的view的，為TextInputLayout，這裡簡單寫個demo：

xml佈局檔案
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools
 
="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop
 
="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context=".MainActivity"
    android:orientation="vertical"
    tools:showIn="@layout/activity_main">

    <android.support.design.widget.TextInputLayout
        android:id="@+id/til_id"
        android:layout_width
 
="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </android.support.design.widget.TextInputLayout>

    <android.support.design.widget.TextInputLayout
        android:id="@+id/til_id2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </android.support.design.widget.TextInputLayout>


</LinearLayout>

接下來，我們就在Activity裡面去實現相關的處理

public class MainActivity extends AppCompatActivity {

    private EditText editText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final TextInputLayout textInputLayout1 = (TextInputLayout) findViewById(R.id.til_id);
        final TextInputLayout textInputLayout2 = (TextInputLayout) findViewById(R.id.til_id2);

        generateEdit(textInputLayout1, "使用者名稱", "使用者名稱輸入不要超過5位",5);
        generateEdit(textInputLayout2,"密碼","密碼長度應小於10位",10);
    }

    private void generateEdit(final TextInputLayout text,String textinput, final String texterror, final int length) {


        editText = text.getEditText();
        text.setHint(textinput);
        editText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                if (s.length() > length) {
                    text.setError(texterror);
                    text.setErrorEnabled(true);
                } else {
                    text.setErrorEnabled(false);
                }
            }

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

            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });
    }
 }   

最終的效果如下：