http://blog.csdn.net/johnny901114/article/details/52662376
一、概述
JakeWharton我想在Android界無人不知,無人不曉的吧, ButterKnife這個框架就是出自他隻手。這個框架我相信很多人都用過,本系列博客就是帶大家更加深入的認識這個框架,ButterKnife截至目前已有1w+的star:
如果我們對於這個優秀框架還是停留在使用階段,那就太可惜。
本系列文章的主要內容如下:
1,ButterKnife是什麼?
2,ButterKnife的作用和功能介紹。
3,ButterKnife的實現原理。
4,自己動手實現個ButterKnife。
二、ButterKnife是什麼?
ButterKnife是一個編譯時的依賴注入框架(compile-time dependency injection framework)用來簡化android中類似findViewById、setOnclickListener等的模板代碼。
比如在寫activity界面的時候常常有如下代碼:
public class MyActivity extents Activity{
private EditText etConsultValidDate;
private TextView tvToolbarCenter;
private TextView tvLeftAction;
private TextView tvRightAction;
private TextView tvConsultTip;
private TextView tvSuggestTime;
private EditText etConsultTitle;
private EditText etConsultDesc;
private EditText etConsultTime;
private EditText etConsultNumber;
private RelativeLayout rlContactInfo;
private LinearLayout llAnswerTime;
private TextView tvAnswerTime, tvAnswerTimePre;
private TextView tvToolbarRight;
private LinearLayout llBottom;
private int from;
private RelativeLayout rlOppositeInfo;
private ImageView ivHeadIcon;
private TextView tvOppositeUsername, tvOppositeDesc;
@Override
protected void initViews() {
tvExpertIdentify = (TextView) findViewById(R.id.tv_expert_identify);
llBottom = (LinearLayout) findViewById(R.id.ll_bottom);
rlOppositeInfo = (RelativeLayout) findViewById(R.id.rl_opposite_info);
ivHeadIcon = (ImageView) findViewById(R.id.iv_head_icon);
tvOppositeUsername = (TextView) findViewById(R.id.tv_opposite_username);
tvOppositeDesc = (TextView) findViewById(R.id.tv_opposite_desc);
rbOppositeScore = (RatingBar) findViewById(R.id.rbar_star);
tvUserCompany = (TextView) findViewById(R.id.tv_user_company);
infoArrow = findViewById(R.id.iv_member_info_arrow);
tvConsultTip = (TextView) findViewById(R.id.tv_consult_tip);
tvLeftAction = (TextView) findViewById(R.id.tv_left_action);
tvRightAction = (TextView) findViewById(R.id.tv_right_action);
llAnswerTime = (LinearLayout) findViewById(R.id.ll_answer_time);
tvAnswerTimePre = (TextView) findViewById(R.id.tv_answer_time_pre);
tvAnswerTime = (TextView) findViewById(R.id.tv_answer_time);
tvLeftAction.setOnClickListener(this);
tvRightAction.setOnClickListener(this);
etConsultTitle = (EditText) findViewById(R.id.et_consult_title);
etConsultDesc = (EditText) findViewById(R.id.et_consult_desc);
etConsultTime = (EditText) findViewById(R.id.et_contact_time);
etConsultNumber = (EditText) findViewById(R.id.et_contact_number);
etConsultValidDate = (EditText) findViewById(R.id.et_consult_valid_day);
tvSuggestTime = (TextView) findViewById(R.id.tv_contact_time);
}
}
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初始化Views大量的沒有技術含量的模板代碼。如果界面比較複雜的話,這樣的代碼變得更多。使用ButterKnife可以很好的簡化上面冗長的代碼。
public class MyActivity extents Activity{
@BindView(R.id.xxx) EditText etConsultValidDate;
@BindView(R.id.xxx) TextView tvToolbarCenter;
@BindView(R.id.xxx) TextView tvLeftAction;
@BindView(R.id.xxx) TextView tvRightAction;
@BindView(R.id.xxx) TextView tvConsultTip;
@BindView(R.id.xxx) TextView tvSuggestTime;
@BindView(R.id.xxx) EditText etConsultTitle;
@BindView(R.id.xxx) EditText etConsultDesc;
@BindView(R.id.xxx) EditText etConsultTime;
@BindView(R.id.xxx) EditText etConsultNumber;
@BindView(R.id.xxx) RelativeLayout rlContactInfo;
@BindView(R.id.xxx) LinearLayout llAnswerTime;
@BindView(R.id.xxx) TextView tvAnswerTime, tvAnswerTimePre;
@BindView(R.id.xxx) TextView tvToolbarRight;
@BindView(R.id.xxx) LinearLayout llBottom;
@BindView(R.id.xxx) RelativeLayout rlOppositeInfo;
@BindView(R.id.xxx) ImageView ivHeadIcon;
@BindView(R.id.xxx) TextView tvOppositeUsername;
@BindView(R.id.xxx) TextView tvOppositeDesc;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.simple_activity);
//初始化Views
ButterKnife.bind(this);
}
}
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相比之下,極大的簡化了View的初始化代碼。
三、ButterKnife的功能介紹(所有的功能)
除了上面的@BindView註解,還其他功能:
1. 使用@BindViews初始化多個View
@BindViews({ R.id.first_name, R.id.middle_name, R.id.last_name })
List nameViews;
2. 使用@OnClick設置監聽事件
@OnClick(R.id.submit)
public void submit(View view) {
// TODO do something…
}
如果不想要submit方法參數可以去掉如:
@OnClick(R.id.submit)
public void submit() {
// TODO do something…
}
View的參數還可以自動轉換,比如給TextView設置點擊事件
@OnClick(R.id.submit)
public void submit(TextView textView) {
// TODO do something…
}
如果是自定義的View可以不指定View Id 如:
public class FancyButton extends Button {
@OnClick
public void onClick() {
// TODO do something!
}
}
3. listView item點擊事件
@OnItemSelected(R.id.list_view)
void onItemSelected(int position) {
// TODO …
}
4. view的onTouchEvent
@OnTouch(R.id.example) boolean onTouch() {
Toast.makeText(this, “Touched!”, Toast.LENGTH_SHORT).show();
return false;
}
5. 監聽EditText的addTextChangedListener
@OnTextChanged(R.id.example) void onTextChanged(CharSequence text) {
Toast.makeText(this, “Text changed: ” + text, Toast.LENGTH_SHORT).show();
}
6. 設置ViewPager的OnPageChangeListener
@OnPageChange(R.id.example_pager) void onPageSelected(int position) {
Toast.makeText(this, “Selected ” + position + “!”, Toast.LENGTH_SHORT).show();
}
7. 設置TextView的OnEditorActionListener(該事件主要用來設置軟鍵盤上的按鈕)
@OnEditorAction(R.id.example) boolean onEditorAction(KeyEvent key) {
Toast.makeText(this, “Pressed: ” + key, Toast.LENGTH_SHORT).show();
return true;
}
8. 設置View的OnFocusChangeListener事件
@OnFocusChange(R.id.example) void onFocusChanged(boolean focused) {
Toast.makeText(this, focused ? “Gained focus” : “Lost focus”, Toast.LENGTH_SHORT).show();
}
9. 設置View的OnLongClickListener長按事件
@OnLongClick(R.id.example) boolean onLongClick() {
Toast.makeText(this, “Long clicked!”, Toast.LENGTH_SHORT).show();
return true;
}
10. 關於資源的綁定
@BindString(R.string.title) String title; //字符串
@BindDrawable(R.drawable.graphic) Drawable graphic; //drawable
@BindColor(R.color.red) int red; // int or ColorStateList field
@BindDimen(R.dimen.spacer) Float spacer; // int (for pixel size) or float (for exact value) field
@BindArray(R.array.countries) String[] countries; 字符串數組
@BindArray(R.array.icons) TypedArray icons;
@BindBool(R.bool.is_tablet) boolean isTablet;
四、ButterKnife的實現原理
通過上面的例子我們知道,要使用ButterKnife首先要在目標代碼使用註解,然後在onCreate生命週期方法裏調用ButterKnife.bind(this);
方法。使用註解沒什麼好說的,那只有看看ButterKnife.bind(this);這個方法是怎麼實現的:
@NonNull @UiThread
public static Unbinder bind(@NonNull Activity target) {
View sourceView = target.getWindow().getDecorView();
return createBinding(target, sourceView);
}
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獲取activity的decorView,然後調用createBinding方法:
private static Unbinder createBinding(@NonNull Object target, @NonNull View source) {
//獲取target的字節碼
Class<?> targetClass = target.getClass();
if (debug) Log.d(TAG, "Looking up binding for " + targetClass.getName());
//搜索構造方法(什麼類的構造方法,下面會分析)
Constructor<? extends Unbinder> constructor = findBindingConstructorForClass(targetClass);
if (constructor == null) {
return Unbinder.EMPTY;
}
//noinspection TryWithIdenticalCatches Resolves to API 19+ only type.
try {
//通過反射構造類實例
return constructor.newInstance(target, source);
} catch (IllegalAccessException e) {
//Ignore Exceptions
}
}
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createBinding方法的第一個參數target就是我們的activity實例,source就是decorView。上面的代碼也比較簡單,我也加上了註釋。這個方法我就不多說了。然後看看findBindingConstructorForClass方法是怎麼實現的:
@Nullable @CheckResult @UiThread
private static Constructor<? extends Unbinder> findBindingConstructorForClass(Class<?> cls) {
//從容器中查找構造方法,如果找到了直接返回。
Constructor<? extends Unbinder> bindingCtor = BINDINGS.get(cls);
if (bindingCtor != null) {
if (debug) Log.d(TAG, "HIT: Cached in binding map.");
return bindingCtor;
}
String clsName = cls.getName();
//如果是android framework裏的類則直接return
if (clsName.startsWith("android.") || clsName.startsWith("java.")) {
if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search.");
return null;
}
try {
//拼接類名,然後獲取該類的字節碼
Class<?> bindingClass = Class.forName(clsName + "_ViewBinding");
//noinspection unchecked
//獲取該類的構造方法
bindingCtor = (Constructor<? extends Unbinder>) bindingClass.getConstructor(cls, View.class);
if (debug) Log.d(TAG, "HIT: Loaded binding class and constructor.");
} catch (ClassNotFoundException e) {
if (debug) Log.d(TAG, "Not found. Trying superclass " + cls.getSuperclass().getName());
bindingCtor = findBindingConstructorForClass(cls.getSuperclass());
} catch (NoSuchMethodException e) {
throw new RuntimeException("Unable to find binding constructor for " + clsName, e);
}
BINDINGS.put(cls, bindingCtor);
return bindingCtor;
}
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findBindingConstructorForClass
方法核心代碼是下面2行代碼:
Class<?> bindingClass = Class.forName(clsName + "_ViewBinding");
bindingCtor = (Constructor<? extends Unbinder>) bindingClass.getConstructor(cls, View.class);
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意思就是target的類型(qualified name)拼接_ViewBinding,然後通過獲取拼接後類的構造方法。那麼clsName + _ViewBinding
這個類是從哪裏來的。
我們把butterKnife的源碼(8.4.0版本)下載下來,build代碼後,查找以_ViewBinding
爲結尾的Java類,發現有十個只有,都位於各自所在項目的build->gernerated->source->apt->debug目錄下。
以裏面的SimpleActivity_ViewBinding
爲例:
// Generated code from Butter Knife. Do not modify!
package com.example.butterknife.library;
public class SimpleActivity_ViewBinding<T extends SimpleActivity> implements Unbinder {
//ignore some code
@UiThread
public SimpleActivity_ViewBinding(final T target, View source) {
target.title = Utils.findRequiredViewAsType(source, R.id.title, "field 'title'", TextView.class);
target.subtitle = Utils.findRequiredViewAsType(source, R.id.subtitle, "field 'subtitle'", TextView.class);
view = Utils.findRequiredView(source, R.id.hello, "field 'hello', method 'sayHello', and method 'sayGetOffMe'");
target.hello = Utils.castView(view, R.id.hello, "field 'hello'", Button.class);
//ignore some code
}
}
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target其實是我們上面的activity,source就是DecorView。發現所有的View的初始化工作全部放在了SimpleActivity_ViewBinding
構造方法裏。
// Generated code from Butter Knife. Do not modify!
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通過這句話我們知道,SimpleActivity_ViewBinding
是ButterKnife生成的。那麼ButterKnife是怎麼生成這個類的呢?
通過一個叫APT(Annotation Processing Tool)工具生成對應的類。
總結下:
1. butterKnife是一個運行時依賴注入框架,有效地幫我們簡化一些重複代碼。
2. butterKnife在ButterKnife.bind方法裏通過反射調用對應的類構造方法執行初始化工作,所以butterKnife並不是完全沒有使用反射,只在這個地方用到了。所以butterKnife的效率也是很高的。對於反射這個技術,不應該持極端態度(徹底不用,或到處濫用)。特別是在android中,到處都是反射,對性能也是有一定的影響的。
3. butterknife使用 apt技術來生成java類。
本系列預計有三篇文章,下一篇文章將介紹在android studio中如何使用apt。最後一篇文章講如何實現調用bind方法就完成view的初始化工作。