通过前3篇文章，大家应该对espresso有了大体上的了解，那么今天我们要深入了解它的API，看看espresso的整体架构。
还是通过espresso cheat sheet来进入本次话题。
Espresso备忘单是您在开发过程中可以使用的快速参考。 这个备忘单包含大多数可用的Matchers，ViewActions和ViewAsertions。
让我们先来看看Matchers 都有哪些API可供我们使用。
android.support.test.espresso.matcher
Classes
BoundedMatcher<T, S extends T> Some matcher sugar that lets you create a matcher for a given type but only process items of a specific subtype of that matcher.
CursorMatchers A collection of Hamcrest matchers that matches a data row in a Cursor.
CursorMatchers.CursorMatcher A Matcher that matches Cursors based on values in their columns.
LayoutMatchers A collection of hamcrest matches to detect typical layout issues.
PreferenceMatchers A collection of hamcrest matchers that match Preferences.
RootMatchers A collection of matchers for Root objects.
ViewMatchers A collection of hamcrest matchers that match Views.
Enums
ViewMatchers.Visibility Enumerates the possible list of values for View.getVisibility().
7个类，1个Eums。接下来我们一个个欣赏谷歌大神的杰作。
BoundedMatcher
一些匹配语法糖，允许您为给定类型创建匹配器，但只能处理该匹配器的特定子类型项。换句话说，就是能够自定义一些匹配器。
举个栗子，以下是一个自定义错误文本匹配器
public final class ErrorTextMatchers {
/**
* Returns a matcher that matches {@link TextView}s based on text property value.
*
* @param stringMatcher {@link Matcher} of {@link String} with text to match
*/
@NonNull
public static Matcher<View> withErrorText(final Matcher<String> stringMatcher) {
return new BoundedMatcher<View, TextView>(TextView.class) {
@Override
public void describeTo(final Description description) {
description.appendText("with error text: ");
stringMatcher.describeTo(description);
}
@Override
public boolean matchesSafely(final TextView textView) {
return stringMatcher.matches(textView.getError().toString());
}
};
}
}
实现的主要细节如下。 我们通过从withErrorText()返回一个BoundedMatcher来确保匹配器只匹配TextView类的子类。 这使得很容易在BoundedMatcher.matchesSafely()中实现匹配逻辑本身：只需从TextView中获取getError()方法并将其送入下一个匹配器。 最后，我们有一个简单的describeTo()方法的实现，它只用于生成调试输出到控制台。
CursorMatchers
Hamcrest的集合匹配器，在Cursor匹配相应的数据行。
源码如下
/**
* Returns a matcher that matches a {@link String} value at a given column index
* in a {@link Cursor}s data row.
* <br>
* @param columnIndex int column index
* @param value a {@link String} value to match
*/
public static CursorMatcher withRowString(int columnIndex, String value) {
return withRowString(columnIndex, is(value));
}
大部分的场景，大多发生于表单或者滚动menu时。
onData(
is(instanceOf(Cursor.class)),
CursorMatchers.withRowString("job_title", is("Barista"))
);
LayoutMatchers hamcrest的集合匹配以检测典型的布局问题。
例如匹配具有椭圆形文本的TextView元素。 如果文本太长，无法适应TextView，
它可以是椭圆形（’Too long’显示为’Too l …’或’… long’）或切断（’Too
long“显示为”Too l“）。 虽然在某些情况下可以接受，但通常表示不好的用户体验。
PreferenceMatchers hamcrest匹配器来匹配一组偏好。
Preference组件其实就是Android常见UI组件与SharePreferences的组合封装实现。
onData(Matchers.<Object>allOf(PreferenceMatchers.withKey("setting-name"))).perform(click());
PreferenceMatchers还有以下方法可以应用到其他场景
withSummary(final int resourceId)
withSummaryText(String summary)
withSummaryText(final Matcher<String> summaryMatcher)
withTitle(final int resourceId)
withTitleText(String title)
withTitleText(final Matcher<String> titleMatcher)
isEnabled()
RootMatchers Root对象的匹配器集合。
匹配root装饰视图匹配给定的视图匹配器。
onView(withText("Text"))
.inRoot(withDecorView(not(is(getActivity().getWindow().getDecorView()))))
.perform(click());
RootMatchers还有以下方法可以应用到其他场景
Public methods
static Matcher isDialog()Matches Roots that are dialogs (i.e.)
static Matcher isFocusable()Matches Roots that can take window focus.
static Matcher isPlatformPopup()Matches Roots that are popups - like autocomplete suggestions or the actionbar spinner.
static Matcher isTouchable()Matches Roots that can receive touch events.
static Matcher withDecorView(Matcher decorViewMatcher)Matches Roots with decor views that match the given view matcher.
ViewMatchers 最重要也是应用最广的匹配器，通过一个或者多个来定位层级里面的控件。
Public methods
static void assertThat(String message, T actual, Matcher matcher) A replacement for MatcherAssert.assertThat that renders View objects nicely.
static void assertThat(T actual, Matcher matcher) A replacement for MatcherAssert.assertThat that renders View objects nicely.
static Matcher hasContentDescription() Returns an Matcher that matches Views with any content description.
static Matcher hasDescendant(Matcher descendantMatcher) Returns a matcher that matches Views based on the presence of a descendant in its view hierarchy.
static Matcher hasErrorText(String expectedError) Returns a matcher that matches EditText based on edit text error string value.
static Matcher hasErrorText(Matcher stringMatcher) Returns a matcher that matches EditText based on edit text error string value.
static Matcher hasFocus() Returns a matcher that matches Views currently have focus.
static Matcher hasImeAction(int imeAction) Returns a matcher that matches views that support input methods (e.g.
static Matcher hasImeAction(Matcher imeActionMatcher) Returns a matcher that matches views that support input methods (e.g.
static Matcher hasLinks() Returns a matcher that matches TextViews that have links.
static Matcher hasSibling(Matcher siblingMatcher) Returns an Matcher that matches Views based on their siblings.
static Matcher isAssignableFrom(Class<? extends View> clazz) Returns a matcher that matches Views which are an instance of or subclass of the provided class.
static Matcher isChecked() Returns a matcher that accepts if and only if the view is a CompoundButton (or subtype of) and is in checked state.
static Matcher isClickable() Returns a matcher that matches Views that are clickable.
static Matcher isCompletelyDisplayed() Returns a matcher which only accepts a view whose height and width fit perfectly within the currently displayed region of this view.
static Matcher isDescendantOfA(Matcher ancestorMatcher) Returns a matcher that matches Views based on the given ancestor type.
static Matcher isDisplayed() Returns a matcher that matches Views that are currently displayed on the screen to the user.
static Matcher isDisplayingAtLeast(int areaPercentage) Returns a matcher which accepts a view so long as a given percentage of that view’s area is not obscured by any other view and is thus visible to the user.
static Matcher isEnabled() Returns a matcher that matches Views that are enabled.
static Matcher isFocusable() Returns a matcher that matches Views that are focusable.
static Matcher isJavascriptEnabled() Returns a matcher that matches WebView if they are evaluating Javascript.
static Matcher isNotChecked() Returns a matcher that accepts if and only if the view is a CompoundButton (or subtype of) and is not in checked state.
static Matcher isRoot() Returns a matcher that matches root View.
static Matcher isSelected() Returns a matcher that matches Views that are selected.
static Matcher supportsInputMethods() Returns a matcher that matches views that support input methods.
static Matcher withChild(Matcher childMatcher) A matcher that returns true if and only if the view’s child is accepted by the provided matcher.
static Matcher withClassName(Matcher classNameMatcher) Returns a matcher that matches Views with class name matching the given matcher.
static Matcher withContentDescription(int resourceId) Returns a Matcher that matches Views based on content description property value.
static Matcher withContentDescription(String text) Returns an Matcher that matches Views based on content description property value.
static Matcher withContentDescription(Matcher<? extends CharSequence> charSequenceMatcher) Returns an Matcher that matches Views based on content description property value.
static Matcher withEffectiveVisibility(ViewMatchers.Visibility visibility) Returns a matcher that matches Views that have “effective” visibility set to the given value.
static Matcher withHint(Matcher stringMatcher) Returns a matcher that matches TextViews based on hint property value.
static Matcher withHint(int resourceId) Returns a matcher that matches a descendant of TextView that is displaying the hint associated with the given resource id.
static Matcher withHint(String hintText) Returns a matcher that matches TextView based on it’s hint property value.
static Matcher withId(Matcher integerMatcher) Returns a matcher that matches Views based on resource ids.
static Matcher withId(int id) Same as withId(is(int)), but attempts to look up resource name of the given id and use an R.id.myView style description with describeTo.
static Matcher withInputType(int inputType) Returns a matcher that matches InputType.
static Matcher withParent(Matcher parentMatcher) A matcher that accepts a view if and only if the view’s parent is accepted by the provided matcher.
static Matcher withResourceName(String name) Returns a matcher that matches Views based on resource id names, (for instance, channel_avatar).
static Matcher withResourceName(Matcher stringMatcher) Returns a matcher that matches Views based on resource id names, (for instance, channel_avatar).
static Matcher withSpinnerText(int resourceId) Returns a matcher that matches a descendant of Spinner that is displaying the string of the selected item associated with the given resource id.
static Matcher withSpinnerText(String text) Returns a matcher that matches Spinner based on it’s selected item’s toString value.
static Matcher withSpinnerText(Matcher stringMatcher) Returns a matcher that matches Spinners based on toString value of the selected item.
static Matcher withTagKey(int key) Returns a matcher that matches View based on tag keys.
static Matcher withTagKey(int key, Matcher objectMatcher) Returns a matcher that matches Views based on tag keys.
static Matcher withTagValue(Matcher tagValueMatcher) Returns a matcher that matches Views based on tag property values.
static Matcher withText(Matcher stringMatcher) Returns a matcher that matches TextViews based on text property value.
static Matcher withText(String text) Returns a matcher that matches TextView based on its text property value.
static Matcher withText(int resourceId) Returns a matcher that matches a descendant of TextView that is displaying the string associated with the given resource id.
ok 这次主要介绍Matchers的API 更多的内容 大家还是要查看官方API去学习。
最新内容请见作者的GitHub页：http://qaseven.github.io/
