Learn New --- re-read C # InDepth (2 ),

Learn New --- re-read C # InDepth (2 ),

A good book, or a deep book, is a new discovery every time you study it.

Okay, I admit that every time I read it, there is a general suspicion that it is always possible ~~

Over the past few years, I have been focusing on the development of the C # client. Gradually, I am confused, confused, and self-righteous. Finally, I am down to review it. Maybe this is also a step-by-step process of self-learning.

I have mentioned so many things before, and I hope that you will not be so impetuous and "deeply understand" C # Every knowledge point of this language. This article summarizes the knowledge in books and provides an overview based on actual application scenarios. If there are any errors, please kindly advise.

The content in this article is relatively simple. Please skip this article.

 

4. Program Closure

The problem with program closure is that the program prejudges and processes certain variables (for personal understanding, please correct me if there are errors or deficiencies) so that some variables are supposed to be used as the value type but changed to the reference type, resulting in data exceptions.

Of course, in most cases, we will not encounter such a problem, but in some cases, we have to pay attention to and analyze the root cause of the problem, and the BUG will never be random.

The following describes the concept of closure through several examples:

Example 4.1

Private void button#click (object sender, RoutedEventArgs e) {int outerVariableCaptured = 5; // external variable (captured) int outerVariableUnCaptured = 50; // external variable (not captured) if (DateTime. now. hour <= 24) {int normalLocalVariable = 1; // local variable of the common method, not an external variable, because there is no anonymous method in its scope. This. txb_Msg.Text + = string. format ("local variable of normal method = {0}", normalLocalVariable) + System. environment. newLine;} Action x = new Action () => {int anonLocal = 2; // The local variable of the anonymous method this. txb_Msg.Text + = string. format ("anonymous method local variable = {0}", anonLocal) + System. environment. newLine; this. txb_Msg.Text + = string. format ("external variables captured in the anonymous method = {0}", outerVariableCaptured) + System. environment. newLine; // The variable outside the scope is called in the anonymous method, so the variable becomes the captured external variable}); this. txb_Msg.Text + = string. format ("uncaptured external variables of common methods = {0}", outerVariableUnCaptured) + System. environment. newLine; x ();}

Output result: local variables of common methods = 1 uncaptured external variables of common methods = 50 local variables of anonymous methods = 2 external variables captured in anonymous methods = 5

In section 4.1, we will help you understand external variables, local variables, and capture concepts. The most important is the captured external variable.

Example 4.2

Private void Button3_Click (object sender, RoutedEventArgs e) {// proof that the declared cycle of the captured local variable is extended. OnCreateDelegate + = MainWindow_OnCreateDelegate; this. Dispatcher. Invoke (OnCreateDelegate (this); // Invoke may be ambiguous here: it is because an event is returned after the Invoke event. // Counter is a value type. Data on the stack will be recycled when it escapes its scope. Is this true? // It is also illustrated from the other side that whether the value type is on the stack or on the stack depends on the type of the object to be created. }

Private Delegate MainWindow_OnCreateDelegate (object sender) {var frm = sender as MainWindow; int Counter = 1; var a = new Action () => {frm. txb_Msg.Text + = string. format ("delegate internal variable value = {0}", Counter) + System. environment. newLine; Counter ++;}); a (); return ;}

Output: delegate internal variable value = 1 delegate internal variable value = 2

In this example, the original life cycle of Counter's value type should be in the MainWindow_OnCreateDelegate (object sender) method, but it has escaped the scope of the method, this is what we call the value type on the stack maritime stack.
It depends on whether the initialization is on the stack or on the stack.

 

Example 4.3

Private void Button4_Click (object sender, RoutedEventArgs e) {// more complex situations var methods = new Action [2]; int outside = 10; // instantiate the variable once for (int I = 0; I <2; I ++) {int inside = 100; // instantiate the variable multiple times methods [I] = new Action () => {this. txb_Msg.Text + = string. format ("Inside Value = {0}; Outside Value = {1}", inside, outside) + System. environment. newLine; inside ++; outside ++; // variables captured by the anonymous method});} methods [0]. invoke (); methods [0]. invoke (); methods [0]. invoke (); methods [1]. invoke ();}

Output result: /*************** Outside variable Memory Sharing *************** Inside Value = 100; outside Value = 10 * Inside Value = 101; Outside Value = 11 * Inside Value = 102; Outside Value = 12 * Inside Value = 100; outside Value = 13 ************************************ ********/

In this example, you have to think about what the values of outside and inside are? Why?
The reason is that inside is initialized multiple times in the For loop. That is to say, For a few times, there are several independent inside objects, although it is a value type.

 

Example 4.4

This example is excerpted from writing high-quality code: 157 suggestions for improving C # programs

Private void Button5_Click (object sender, RoutedEventArgs e) {// closure trap var methods = new Action [2]; for (int I = 0; I <2; I ++) {int inside = I; // instantiate the variable multiple times methods [I] = new Action () => {this. txb_Msg.Text + = string. format ("Inside Value = {0}; Index Value = {1}", inside, I) + System. environment. newLine;});} methods [0]. invoke (); methods [1]. invoke (); /***************** closure trap ******************** ** When I is used, I is the shared variable (captured external variable), so the maximum value of I is always output. * When the Inside value is used, the Inside variable is an internal variable. Every time an object is created, the inside value is generated again. Therefore, the Inside value increases progressively, that is, the value of I in the cache. * For IL, it creates Tempclass. I to replace I, resulting in I value sharing. **************************************** ****/}

Output result: Inside Value = 0; Index Value = 2 Inside Value = 1; Index Value = 2

In fact, if we use ILDasm, for the I object, IL generates a DisplayClass (that is, a name) class, which is the most common cause: I changes to the reference type, and the data is abnormal.

 

 

Continuous update: Sample Code download

Help me, ask what is re-reading and non-re-reading in English? The better.

The pronunciation rules of English words re-reading rules are mainly for re-reading syllables. Therefore, how to determine the re-reading syllables of two-syllable words and multi-syllable words, it becomes the key to implementing the word "seeing is capable of reading.

Which of the two-syllable and multi-syllable words re-reading often involves the structure of words, so it is necessary to first introduce the main word building methods.

There are many ways to form English words, but there are three main methods: (1) the fix is legal: the prefix or suffix is used to form another word. For example: luck (luck) → lucky (lucky), unluky (unfortunately ). (2) Conversion Method: converts one word class to another. For example, water (n. water) → water (v. Watering ). (3) Synthesis: two or more words are combined into one word. For example: book + bag → bookbag (bag); mother + in + law → mother-in-law (mother-in-law ).

Ii. Rereading of two-syllable words

(1) general tendency of two-syllable word re-reading

1. Two-syllable verbs tend to repeat the second syllable. For example, absorb, behave, forget, and receive ).

2. disyllabic words other than verbs tend to repeat the first syllable. Example: custom (n. habits), distant (adj. distant), second (num. (2), terminate (pron. many), often (adv. frequently), into (prep. enter), after (conj. ...... Later ).

Suffixes of nouns, adjectives, and adverbs are mostly unrereded, such as-er,-or,-ess,-ism? -Tion? -Sion,-ssion? -Ment? -Ship? -Hood? -Age? -Ure? -Dom? -Ey? -Ance? -Our? -Ent? -Ace? -Ow? -Noun suffixes such as ic (s);-less? -Ish? -Ive? -Ous? -Able? -Visible? -Ic? -Some? -Like? -En-ed? -Al? -Ant,-ful? -Ing? -Ty? -Suffixes of adjectives such as ly. -Ly? -Ward (s),-wise, and other adverbs suffix. This further increases the tendency of such words to repeat the first syllable. Just a few examples. Nouns: actor, nation (country), adjective: useful (useful), dirty (dirty), adverbs: really (true), and number words: twenty (20 ).

3. Some words can be both verb and noun or adjective. When a verb is used, the second syllable is reread. When a noun or adjective is used, the first syllable is reread. This shows a clear comparison between the two tendencies. For example, when-rekord is used as the verb "record", read [ri 'k? : D) read [-rek? D ?; Present reads [prizent] As the verb "present" and ['prez? Nt 〔? B 'sent, which is used as the adjective "absent 〔′? Bs? Nt 〕.

(2) Factors Affecting the word-building tendency of double-syllable words

The two-syllable verb tends to reread the second syllable, while other double-syllable words tend to reread the first syllable, but this does not mean that all double-syllable words are in this way. According to statistics, 90% of the two-syllable verbs conform to the tendency of re-reading the second syllable, and about 60% of the non-verb two-syllable words conform to the tendency of re-reading the first syllable.

The re-reading of two-syllable words is also affected by the word structure.

1. Influences of suffixes

① With-en? -Er-,-ish,-le,-y,-ow, and other non-re-reading suffixes. The second syllable is not re-stressed, and the first syllable is re-stressed. For example, happen, open, finish, struggle, carry, swallow, and borrow ).

② Adverbs with Prefix a-, be-, to-, ex-, and so on, adjectives, prepositions, hyphens, and nouns ending with-ee and-self ...... remaining full text>

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Farmer-learn new
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Farmer-learn new
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