最近在使用知乎Android客户端的时候发现一个十分好玩的UI。以下图:
css
其实不难看出,知乎app使用了大量原生的Android Material Design控件,包括ToolBar、DrawerLayout、NavigationView、CardView、SwipeRefreshLayout、FloatingActionButton、BottomNavigationBar等等等等。
顺着这个思路,我很快找到上图这个EditText获取到焦点后,hint文本的动画效果实际上也是来源于Material Design库中的一个控件——TextInputLayout。下面简单介绍一下这个控件的用法以及用途。java
要使用这个控件,须要引入appcompat-v7以及Design Support Library两个库。android
dependencies {
compile 'com.android.support:appcompat-v7:23.1.1'
compile 'com.android.support:design:23.1.1'
}
首先咱们必须了解的是,TextInputLayout
继承于LinearLayout
,只能拥有一个直接的ChildView(相似于ScrollView
),且这个ChildView只能是EditText
。bash
<android.support.design.widget.TextInputLayout android:layout_width="match_parent" android:layout_height="wrap_content">
<EditText android:id="@+id/edt_password" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="password"/>
</android.support.design.widget.TextInputLayout>
通常来讲,EditText
有一个hint
属性,当Edittext
中没有内容时,就会显示文字提示。一旦用户开始输入时,这个文字提示就会消失,取而代之地显示用户的输入。这样有一个坏处就是用户就没法了解到当前本身输入的是关于什么的信息。
而TextInputLayout解决了这个问题,用户开始输入时,hint
文字提示会变成EditText
上方的标签,并伴随一个向上平移+缩放的优雅动画。
就这样,就能够实现图1的效果。app
colorAccent
属性即可以指定TextInputLayout
的标签字体颜色以及EditText
的下划线颜色。 <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar"> <item name="colorAccent">#3498db</item> </style>
实际项目中,咱们须要对用户的输入进行校验(例如 邮箱格式、密码长度、手机号码等),对用户的输入(即mTextInputLayout.getEditText().getText().toString()
)在后台进行验证,若是检查到用户输入不合法,能够经过setError()
显示输入错误提示,以及setErrorEnabled(fasle)
清除错误提示。ide
public void onClick(View v) {
hideKeyboard();
String username = usernameWrapper.getEditText().getText().toString();
String password = usernameWrapper.getEditText().getText().toString();
if (!validateEmail(username)) {
usernameWrapper.setError("Not a valid email address!");
} else if (!validatePassword(password)) {
passwordWrapper.setError("Not a valid password!");
} else {
usernameWrapper.setErrorEnabled(false);
passwordWrapper.setErrorEnabled(false);
doLogin();
}
}
`
错误提示的效果是:标签字体颜色变红,且在EditText下方出现错误信息的标签,这时整个TextInputLayout的高度也会发生变化。以下图:
布局
/** * Layout which wraps an {@link android.widget.EditText} (or descendant) to show a floating label * when the hint is hidden due to the user inputting text. * * Also supports showing an error via {@link #setErrorEnabled(boolean)} and * {@link #setError(CharSequence)}. */ public class TextInputLayout extends LinearLayout { ...... @Override public void addView(View child, int index, ViewGroup.LayoutParams params) { if (child instanceof EditText) { setEditText((EditText) child); super.addView(child, 0, updateEditTextMargin(params)); } else { // Carry on adding the View... super.addView(child, index, params); } } private void setEditText(EditText editText) { // Add a TextWatcher so that we know when the text input has changed mEditText.addTextChangedListener(new TextWatcher() { @Override public void afterTextChanged(Editable s) { updateLabelVisibility(true); if (mCounterEnabled) { updateCounter(s.length()); } } @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) {} @Override public void onTextChanged(CharSequence s, int start, int before, int count) {} }); ...... } }
/** * Layout which wraps an {@link android.widget.EditText} (or descendant) to show a floating label * when the hint is hidden due to the user inputting text. * * Also supports showing an error via {@link #setErrorEnabled(boolean)} and * {@link #setError(CharSequence)}. */ public class TextInputLayout extends LinearLayout { ...... @Override public void addView(View child, int index, ViewGroup.LayoutParams params) { if (child instanceof EditText) { setEditText((EditText) child); super.addView(child, 0, updateEditTextMargin(params)); } else { // Carry on adding the View... super.addView(child, index, params); } } private void setEditText(EditText editText) { // Add a TextWatcher so that we know when the text input has changed mEditText.addTextChangedListener(new TextWatcher() { @Override public void afterTextChanged(Editable s) { updateLabelVisibility(true); if (mCounterEnabled) { updateCounter(s.length()); } } @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) {} @Override public void onTextChanged(CharSequence s, int start, int before, int count) {} }); ...... } }
能够看出,TextInputLayout为内部的EditText设置了一个监听器,监听到有文本输入的时候,经过updateLabelVisibility(true);
将EditText的hint转变成上方的标签。字体
private void updateLabelVisibility(boolean animate) { ...... if (hasText || isFocused || isErrorShowing) { // We should be showing the label so do so if it isn't already collapseHint(animate); } else { // We should not be showing the label so hide it expandHint(animate); } }
private void updateLabelVisibility(boolean animate) { ...... if (hasText || isFocused || isErrorShowing) { // We should be showing the label so do so if it isn't already collapseHint(animate); } else { // We should not be showing the label so hide it expandHint(animate); } }
而在collapseHint(boolean animate)
和expandHint(boolean animate)
内部都是执行animateToExpansionFraction(final float target)
方法,经过属性动画来控制TextInputLayout里面EditText上方hint标签的显示。动画
private void animateToExpansionFraction(final float target) { ...... mAnimator.setFloatValues(mCollapsingTextHelper.getExpansionFraction(), target); mAnimator.start(); }
private void animateToExpansionFraction(final float target) { ...... mAnimator.setFloatValues(mCollapsingTextHelper.getExpansionFraction(), target); mAnimator.start(); }
TextInputLayout的简单使用,是Google推出的整个Material Design库的一个缩影:Google将UI视觉效果设计得华丽且流畅,同时代码封装更为优雅,开发者只须要在layout.xml中写好布局文件,就能够轻松在手机屏幕上展示出魔法般的动画效果,实在是妙趣横生。ui