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In this article Xiaobian for you to introduce in detail "Android development dart is value transfer or reference transfer", the content is detailed, the steps are clear, the details are handled properly, I hope that this "Android development dart is value transfer or reference transfer" article can help you solve doubts, the following follow the editor's ideas slowly in-depth, together to learn new knowledge.

Will the Java and Android basic Jvm virtual machine messageQueue block the zigzag print tree of ui thread object locks and class locks?

Whether the two-sided questions of Flutter and Dartdart are value-passing or reference the relationship between Widget and the relationship between element and RenderObject widget the relationship between root nodes mixin extends implement (except for extends) has not been used much. Jvm memory model (it feels like the interviewer pitied me because I didn't know how to ask. =) Future and microtask execution sequence dart.. The usage of (hardly used). ) await for (not used. )

To tell you the truth, the first, third and sixth words I prepared should be able to answer, but I haven't touched Flutter for more than a month. I forgot it was almost the same. Write down the answer of the second side later, hoping to help the later generations. In addition, good maintenance of GitHub and blog is very important. People like me who write demo easily and delete GG directly.

1. Is dart value passing or reference passing?

First of all, let's come to the conclusion that dart is reference passing. Let's take a look at a piece of code.

Main () {

Test a = new Test (5)

Print (the initial value of "an is: ${a.value}")

SetValue (a)

Print ("the value of modified an is: ${a.value}")

}

Class Test {

Int value = 1

Test (int newValue) {

This.value = newValue

}

}

SetValue (Test s) {

Print ("modify value to 100")

S.value = 100

}

The output is as follows:

The initial value of an is: 5

Modify value to 100

The value of modified an is: 100

From this you can see that it is a reference pass, and if you just copy an object, the a value in the main function will not change.

Some people may refute me with the following code:

Main () {

Int s = 6

SetValue (s)

Print (s); / / output 6 instead of 7

}

Class Test {

Int value = 1

Test (int newValue) {

This.value = newValue

}

}

SetValue (int s) {

S + = 1

}

You see, this output is not 6, in dart everything is an object, if it is a reference pass, then why is 6 ah.

The answer is that in the setValue () method, the parameter s is not actually the same object as the s we initialized int s = 6, except that they now refer to the same memory area, and then when s + = 1 is called in setValue (), the object in this memory region performs the + 1 operation, and then a new object is generated in the heap (analogy java), and s points to this object. So the s parameter simply copies the memory address of the s in the main function, such as in java:

Public class Test {

Public static void main (String [] args) {

Test a = new Test ()

Test b = a

B = new Test ()

}

}

We just need to remember that the parameter passes the memory address, and if the object on this memory address is modified, the values of variables in other locations that refer to that memory address will also be changed. It is important to remember that everything in dart is an object.

Secretly, I think the interviewer's interview in this place is not good. If you don't encounter any bug, you don't have time to pay attention to this when the business is busy. The interviewer can show these two situations and then ask the interviewer what the reason is. And then I can answer it. Crying Haw.

2. The relationship between Widget and element and RenderObject

First of all, I gave a detailed account of the situation at that time. The interviewer asked me if there was an one-to-many relationship between Widget and Element, and what the relationship would be after the addition of a Widget.

There is still no good answer to this part, now it is just a guess, if you add a widget,Element tree to traverse all the subsequent Element to see if the type has changed, and then rebuild the RenderObject.

There should still be an one-to-one relationship between Element and Widget, because the context of each Widget is unique. Write it down when you think about it.

3. Root node of widget tree

Still failed to understand what the interviewer meant. If you have any students who can understand, please comment and let me know. Now I understand that the interviewer should mean the Widget of the runApp () method. I wanted to say it at the time, but I forgot what the name of this method was.

4. The relationship between mixin extends implement

This part can refer to the article of Denver Nuggets, which is as high-yielding as that. Flutter Dart mixins explores Flutter Dart Grammar (1): the usage and difference of extends, implements and with

6. Future and microtask execution sequence also refer to Novak's article to gain an in-depth understanding of Flutter's isolate (1)-event loop (event loop) and code execution sequence-create your own isolate and learn more about Flutter's isolate (3)-Flutter's thread model (threading model) learn more about Flutter's isolate (4)-use Compute to write isolates.

7. In dart.. What is the cascade symbol.. It allows you to operate on the same objects continuously, not only to call functions continuously, but also to access methods continuously, which avoids creating temporary variables and writes smoother code. Stream programming is more in line with modern programming habits and programming styles:

Main () {

Tree tree = new Tree (1)

Tree..test1 = 1..test2 = 5

Print (tree.test1)

Print (tree.test2)

}

Class Tree {

Int value

Int test1 = 2

Int test2 = 3

Tree (int a) {

This.value = a

}

}

8. Await for uses an official document first.

Await-forAs every Dart programmer knows, the for-in loop plays well with iterables. Similarly, the await-for loop is designed to play well with streams.Given a stream, one can loop over its values:Every time an element is added to the stream, the loop body is run. After each iteration, the function enclosing the loop suspends until the next element is available or the stream is done. Just like await expressions, await-for loops can only appear inside asynchronous functions.

The approximate meaning is that await for constantly fetches the data in the stream stream and then performs the operations in the body of the loop.

Stream stream = new Stream.fromIterable (['unhappy', 'interview','no', 'pass'])

Main () async {

Print ('my feet were burned by boiling water in the morning')

Await for (String s in stream) {

Print (s)

}

Print ('I haven't eaten in the evening')

}

Output as

My feet were burned by boiling water in the morning.

Not happy

Interview

no

Pass

I haven't eaten in the evening.

The functions of await for and listen are very similar. They both acquire data from the stream and output them, but as shown by await in await for, if the stream is not passed, it will always be blocked in this position. No meal on the top is the last output. Here is an example of listen, which is easy to understand.

Stream stream = new Stream.fromIterable (['unhappy', 'interview','no', 'pass'])

Main () {

Print ('my feet were burned by boiling water in the morning')

Stream.listen ((s) {print (s);})

Print ('I haven't eaten in the evening')

}

Output as

My feet were burned by boiling water in the morning.

I haven't eaten in the evening.

Not happy

Interview

no

Pass

So await for is generally used until when the stream is completed, and you must wait for the delivery to complete before you can use it, otherwise it will block all the time, causing problems similar to Android ANR.

After reading this, the article "dart is value transfer or reference transfer in Android development" has been introduced. If you want to master the knowledge points of this article, you still need to practice and use it yourself. If you want to know more about related articles, welcome to follow the industry information channel.

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