Alex

Activity启动模式

Wed, 18 May 2022 00:00:00 +0000

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版本	修改内容	日期
V1.0.0	初始版本	2022.5.18

Activity启动模式

Android系统为Activity提供了四种启动模式：

标准模式(standard)
栈顶复用模式(singleTop)
栈内复用模式(singleTask)
单例模式(singleInstance)

Activity以栈的方式进行管理，栈是一种先进后出的数据结构，也就是先启动的Activity，都是最后销毁。每按一次返回，退出一个Activity。

Activity的启动模式会影响栈的管理以及Activity真实的生命周期，方便APP处理不同的业务场景。

先简单介绍四种模式的定义

标准模式(standard)

Android创建Activity的默认模式，如果没有为Activity设置启动模式的话，默认就是标准模式。每次启动一个Activity都会创建一个新的实例入栈，无论这个实例是否存在。

栈顶复用模式(singleTop)

有两种处理情况：

要创建的Activity已经处于栈顶，此时会直接复用栈顶的Activity，不会再创建新的Activity。
要创建的Activity已经存在栈中，但是不处于栈顶；此时会创建一个新的Activity实例入栈。

栈内复用模式(singleTask)

要创建的Activity已经处于栈中，此时不会创建新的Activity，而是将栈中的Activity上面的其他Activity销毁，使它成为栈顶Activity。

单例模式(singleInstance)

singleInstance全局单例模式，singleTask的加强模式。除了具有singleTask的特性外，此模式Activity只能单独位于一个Activity栈。经常使用于系统应用，比如，Launch、锁屏键的应用，整个系统中只有一个。

标准模式(standard)

Android新建的所有Activity默认启动模式都是standard，按照创建的先后顺序，依次入栈，采用先进后出的方式管理。不管栈中是否已存在Activity实例，都会创建新的Activity实例再入栈。

接下来，我们通过代码介绍standard模式，大体思路如下：

先声明一个Activity，应用启动时创建Activity实例并入栈
给Activity添加按钮点击事件，当用户点击按钮时创建Activity实例并入栈。
用户手动点击系统返回键，Activity实例出栈，Activity实例的生命周期结束。
通过日志观察Activity栈和Activity实例的运行情况。

声明Activity

先在manifest中声明Activity

<activity android:name="com.wangxb.app.launchmode.MainActivity">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

定义Activity界面，声明一个按钮 ```xml

Kotlin

Thu, 24 Mar 2022 00:00:00 +0000

Learning materials

学习资料

Overview

概述

You can use the following materials and resources for learning Kotlin:

您可以使用下述文档和资源学习 Kotlin：

Basic syntax – get a quick overview of the Kotlin syntax.
基本语法 —— 快速了解Kotlin语法
Idioms – learn how to write idiomatic Kotlin code for popular cases.
编码习惯 —— 学习常用的Kotlin编码习惯
Java to Kotlin migration guide: Strings – learn how to perform typical tasks with strings in Java and Kotlin.
Java 到 Kotlin 迁移指南：字符串 —— 了解如何在 Java 和 Kotlin 中使用字符串执行典型任务。
Kotlin Koans – complete exercises to learn the Kotlin syntax. Each exercise is created as a failing unit test and your job is to make it pass.
Kotlin Koans —— 学习 Kotlin 语法的完整练习。每个练习都是作为失败的单元测试创建的，你的工作就是让它通过。
Kotlin by example – review a set of small and simple annotated examples for the Kotlin syntax.
Kotlin 示例 —— 查看一组小而简单的 Kotlin 语法注释示例。
Kotlin Basics track – learn all the Kotlin essentials while creating working applications step by step on JetBrains Academy.
Kotlin Basics track – 在 JetBrains Academy 上逐步创建工作应用程序的同时学习所有 Kotlin 基础知识。
Advent of Code puzzles – learn idiomatic Kotlin and practice your language skills by completing short and fun tasks.
Advent of Code 谜题 - 学习惯用的 Kotlin 并通过完成简短而有趣的任务来练习您的语言技能。
Kotlin books – find books we’ve reviewed and recommend for learning Kotlin.
Kotlin 书籍 - 查找我们为学习 Kotlin 所审查和推荐的书籍。
Kotlin hands-on tutorials – complete long-form tutorials to fully grasp a technology. These tutorials guide you through a self-contained project related to a specific topic.
Kotlin 动手教程——完整的长篇教程以完全掌握一项技术。这些教程指导您完成与特定主题相关的独立项目。
Kotlin for Java Developers – course for developers with experience in Java. It shows the similarities between the two languages and focuses on what’s going to be different.
Kotlin for Java Developers – 面向具有 Java 经验的开发人员的课程。它显示了两种语言之间的相似之处，并着重于不同之处。
Kotlin documentation in the PDF format – read the whole documentation offline.
PDF 格式的 Kotlin 文档 – 离线阅读整个文档。

Basic syntax

基本语法

This is a collection of basic syntax elements with examples. At the end of every section, you’ll find a link to a detailed description of the related topic.

这是带有示例的基本语法元素的集合。在每个部分的末尾，您都会找到指向相关主题详细说明的链接。

You can also learn all the Kotlin essentials with the free Kotlin Basics track on JetBrains Academy.

您还可以通过 JetBrains Academy 上的免费 Kotlin Basics 轨道学习所有 Kotlin 基础知识。

Package definition and imports

包定义和导入

Package specification should be at the top of the source file.

包定义应该在源文件的顶部。

package my.demo

import kotlin.text.*

// ...

It is not required to match directories and packages: source files can be placed arbitrarily in the file system.

不需要匹配目录和包：源文件可以任意放置在文件系统中。

See Packages.

Program entry point

程序进入点

An entry point of a Kotlin application is the main function.

Kotlin 应用程序的入口点是 main 函数。

fun main() {
    println("Hello world!")
}

Another form of main accepts a variable number of String arguments.

main 的另一种形式接受可变数量的 String 参数。

fun main(args: Array<String>) {
    println(args.contentToString())
}

Print to the standard output

打印到标准输出

print prints its argument to the standard output.

print 将其参数打印到标准输出。

fun main() {
    print("Hello ")
    print("world!")
}

println prints its arguments and adds a line break, so that the next thing you print appears on the next line.

println 打印它的参数并添加一个换行符，以便您打印的下一个内容出现在下一行。

fun main() {
    println("Hello world!")
    println(42)
}

Functions

函数

A function with two Int parameters and Int return type.

具有两个 Int 参数和 Int 返回类型的函数。

fun sum(a: Int, b: Int): Int {
    return a + b
}

fun main() {
    print("sum of 3 and 5 is ")
    println(sum(3, 5))
}

A function body can be an expression. Its return type is inferred.

函数体可以是表达式，它会自动推断返回类型。

fun sum(a: Int, b: Int) = a + b

fun main() {
    println("sum of 19 an 23 is ${sum(19, 23)}")
}

A function that returns no meaningful value.

一个返回无意义值的函数。

fun printSum(a: Int, b: Int): Unit {
    println("sum of $a and $b is ${a + b}")
}

fun main() {
    printSum(-1, 8)
}

Unit return type can be omitted.

Unit 返回类型可以省略。

fun printSum(a: Int, b: Int) {
    println("sum of $a and $b is ${a + b}")
}

fun main() {
    printSum(-1, 8)
}

See Functions.

Variables

变量

Read-only local variables are defined using the keyword val. They can be assigned a value only once.

只读局部变量使用关键字 val 定义，它们只能被赋值一次。

fun main() {
    val a: Int = 1    // immediate assignment
    val b = 2    // `Int` type is inferred
    val c: Int   // Type required when no initializer is provided
    c = 3        // deferred assignment
    println("a = $a, b = $b, c = $c")
}

Variables that can be reassigned use the var keyword.

可以重新赋值的变量使用 var 关键字。

fun main() {
    var x = 5
    x += 1
    println("x = $x")
}

You can declare variables at the top level.

您可以在顶层声明变量。

val PI = 3.14
var x = 0

fun incrementX() {
    x += 1
}

fun main() {
    println("x = $x; PI = $PI")
    incrementX()
    println("incrementX()")
    println("x = $x; PI = $PI")
}

Creating classes and instances

创建类和实例

To define a class, use the class keyword.

要定义一个类，请使用 class 关键字。

class Shape

Properties of a class can be listed in its declaration or body.

类的属性可以在其声明或主体中列出。

class Rectangle(var height: Double, var length: Double) {
    var perimeter = (height + length) * 2
}

The default constructor with parameters listed in the class declaration is available automatically.

含类声明且带参数的默认构造函数将自动可用。

class Rectangle(var height: Double, var length: Double) {
    var perimeter = (height + length) * 2
}

fun main() {
    var rectangle = Rectangle(5.0, 2.0)
    println("The perimeter is ${rectangle.perimeter}")
}

Inheritance between classes is declared by a colon (:). Classes are final by default; to make a class inheritable, mark it as open.

类之间的继承由冒号 (:) 声明。默认情况下，类是最终的；要使类可继承，请将其标记为 open 。

open class Shape

class Rectangle(var height: Double, var length: Double): Shape() {
    var perimeter = (height + length) * 2
}

See classes and objects and instances.

Comments

注释

Just like most modern languages, Kotlin supports single-line (or end-of-line) and multi-line (block) comments.

就像大多数现代语言一样，Kotlin 支持单行（或行尾）和多行（块）注释。

// This is an end-of-line comment

/* This is a block comment
   on multiple lines. */

Block comments in Kotlin can be nested.

Kotlin 中的块注释可以嵌套。

/* The comment starts here
/* contains a nested comment */
and ends here. */

See Documenting Kotlin Code for information on the documentation comment syntax.

有关文档注释语法的信息，请参阅 Documenting Kotlin Code 。

String templates

字符串模板

fun main() {
    var a = 1
    
    // simple name in template:
    val s1 = "a is $a"
    
    a = 2
    
    // arbitrary expression in template:
    val s2 = "${s1.replace("is", "was")}, but now is $a"
    
    println(s2)
}

See String templates for details.

Conditional expressions

条件表达式

fun maxOf(a: Int, b: Int): Int {
    if (a > b) {
        return a
    } else {
        return b
    }
}

fun main() {
    prinln("max of 0 and 42 is ${maxOf(0, 42)}")
}

In Kotlin, if can also be used as an expression.

在 Kotlin 中，if 也可以用作表达式。

fun maxOf(a: Int, b: Int) = if (a > b) a else b

fun main() {
    prinln("max of 0 and 42 is ${maxOf(0, 42)}")
}

See if-expressions.

for loop

fun main() {
    val items = listOf("apple", "banana", "kiwifruit")
    for (item in items) {
        println(item)
    }
}

fun main() {
    val items = listOf("apple", "banana", "kiwifruit")
    for (index in items.indices) {
        println("item at $index is ${items[index]}")
    }
}

See for loop.

while loop

fun main() {
    val items = listOf("apple", "banana", "kiwifruit")
    var index = 0
    while (index < items.size) {
        println("item at $index is ${items[index]}")
        index++
    }
}

See while loop.

when expression

fun describe(obj: Any) String = 
	when(obj) {
        1           -> "One"
        "Hello"     -> "Greeting"
        is Long     -> "Long"
        !is String  -> "Not a string"
        else        -> "Unknown"
    }

fun main() {
    println(describe(1))
    println(describe("Hello"))
    println(describe("1000L"))
    println(describe(2))
    println(describe("other"))
}

See when expression.

Ranges

范围

Check if a number is within a range using in operator.

使用 in 运算符检查数字是否在范围内。

fun main() {
    val x = 10
    val y = 9
    if (x in 1..y+1) {
        println("fits in range")
    }
}

Check if a number is out of range.

检查数字是否超出范围。

fun main() {
    val list = listOf("a", "b", "c")
    
    if (-1 !in 0..list.lastIndex) {
        println("-1 is out of range")
    }
    
    if (list.size !in list.indices) {
        println("list size is out of valid list indices range, too")
    }
}

Iterate over a range.

迭代一个范围

fun main() {
    for (x in 1..5) {
        print(x)
    }
}

Or over a progression.

或者跳过一个处理元素

fun main() {
    for (x in 1..10 step 2) {
        print(x)
    }
    println()
    for (x in 9 downTo 0 step 3) {
        print(x)
    }
}

See Ranges and progressions.

Collections

Iterate over a collection.

迭代一个集合

fun main() {
    val items = listOf("apple", "banana", "kiwifruit")
    for (item in items) {
        println(item)
    }
}

Check if a collection contains an object using in operator.

使用 in 运算符检查集合是否包含一个对象。

fun main() {
    val items = setOf("apple", "banana", "kiwifruit")
    when {
        "orange" in items -> println("juicy")
        "apple" in items -> println("apple is fine too")
    }
}

Using lambda expressions to filter and map collections:

使用 lambda 表达式过滤和映射集合：

fun main() {
    val fruits = listOf("banana", "avocado", "apple", "kiwifruit")
    fruits
    	.filter { it.startsWith("a") }
        .sortedBy { it }
        .map { it.uppercase() }
        .forEach { println(it) }
}

See Collections overview.

Nullable values and null checks

可空值和空检查

A reference must be explicitly marked as nullable when null value is possible. Nullable type names have ? at the end.

当变量值可能为 null 时，必须将其标记为可空类型。可空类型 ? 在末尾。

Return null if str does not hold an integer:

如果 str 不包含整数，则返回 null：

fun parseInt(str : String): Int? {
    // ...
}

Use a function returning nullable value:

使用返回可为空值的函数：

fun parseInt(str : String): Int? {
    return str.toIntOrNull()
}

fun printProduct(arg1: String, arg2: String) {
    val x = parseInt(arg1)
    val y = parseInt(arg2)
    
    // Using `x * y` yields error because they may hold nulls.
    if (x != null && y != null) {
        // x and y are automatically cast to non-nullable after null check
        println(x * y)
    } else {
        println("'$arg1' or '$arg2' is not a number")
    }
}

fun main() {
    printProduct("6", "7")
    printProduct("a", "7")
    printProduct("a", "b")
}

fun parseInt(str : String): Int? {
    return str.toIntOrNull()
}

fun printProduct(arg1: String, arg2: String) {
    val x = parseInt(arg1)
    val y = parseInt(arg2)
    
    if (x == null) {
        println("Wrong number format in arg1: '$arg1'")
        return
    }
    
    if (y == null) {
        println("Wrong number format in arg2: '$arg2'")
        return
    }
    
    // x and y are automatically cast to non-nullable after null check
    println(x * y)
}

fun main() {
    printProduct("6", "7")
    printProduct("a", "7")
    printProduct("a", "b")
}

See Null-safety.

Type checks and automatic casts

类型检查和自动转换

The is operator checks if an expression is an instance of a type. If an immutable local variable or property is checked for a specific type, there’s no need to cast it explicitly:

is 运算符检查表达式是否为类型的实例。如果为特定类型检查了不可变的局部变量或属性，则无需显式强制转换它：

fun getStringLength(obj: Any): Int? {
    if (obj is String) {
        // `obj` is automatically cast to `String` in this branch
        return obj.length
    }
    
    // `obj` is still of type `Any` outside of the type-checked branch
    return null
}

fun main() {
    fun printLength(obj: Any) {
        println("Getting the legnth of '$obj'. Result: ${getStringLength(obj) ?: "Error: The object is not a String"}")
    }
    
    printLength("Incomprehensibilities")
    printLength(1000)
    printLength(listOf(Any()))
}

fun getStringLength(obj: Any): Int? {
    if (obj !is String) return null
    
    // `obj` is automatically cast to `String` in this branch
    return obj.length
}

fun main() {
    fun printLength(obj: Any) {
        println("Getting the legnth of '$obj'. Result: ${getStringLength(obj) ?: "Error: The object is not a String"}")
    }
    
    printLength("Incomprehensibilities")
    printLength(1000)
    printLength(listOf(Any()))
}

or even

fun getStringLength(obj: Any): Int? {
    // `obj` is automatically cast to `String` on the rigth-hand side of `&&`
    if (obj is String && obj.length > 0) {
 		return obj.length       
    }
    
    return null
}

fun main() {
    fun printLength(obj: Any) {
        println("Getting the legnth of '$obj'. Result: ${getStringLength(obj) ?: "Error: The object is not a String"}")
    }
    
    printLength("Incomprehensibilities")
    printLength(1000)
    printLength(listOf(Any()))
}

See Classes and Type casts.

Idioms

A collection of random and frequently used idioms in Kotlin. If you have a favorite idiom, contribute it by sending a pull request.

Kotlin 中随机且常用的idioms集合。如果您有最喜欢的编码习惯，请通过发送拉取请求来贡献它。

Create DTOs (POJOs/POCOs)

Launcher3

Fri, 18 Mar 2022 00:00:00 +0000

https://www.cnblogs.com/l2rf/p/5850341.html

https://www.jianshu.com/p/968e2339ee5f

https://github.com/Launcher3-dev/Launcher3

Logcat

Tue, 15 Mar 2022 00:00:00 +0000

https://www.cnblogs.com/Ph-one/p/10858579.html

https://www.cnblogs.com/JianXu/p/5468839.html

Aosp源码下载

Sat, 12 Mar 2022 00:00:00 +0000

问题1

// 执行
> repo init -u https://mirrors.tuna.tsinghua.edu.cn/git/AOSP/platform/manifest -b android-11.0.0_r48
// 报错
/usr/bin/env: ‘python’: No such file or directory

解决方案

> whereis python3
python3: /usr/bin/python3 /usr/bin/python3.6 /usr/bin/python3.6m /usr/lib/python3.8 /usr/lib/python3.7 /usr/lib/python3 /usr/lib/python3.6 /etc/python3 /etc/python3.6 /usr/local/lib/python3.6 /usr/share/python3 /mnt/c/Users/joyki/AppData/Local/Microsoft/WindowsApps/python3.exe /usr/share/man/man1/python3.1.gz

> sudo ln -s /usr/bin/python3 /usr/bin/python

问题2

// 执行
> repo init -u https://mirrors.tuna.tsinghua.edu.cn/git/AOSP/platform/manifest -b android-11.0.0_r48
// 报错
Downloading Repo source from https://mirrors.tuna.tsinghua.edu.cn/git/git-repo
fatal: unable to access 'https://mirrors.tuna.tsinghua.edu.cn/git/git-repo/': server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
repo: error: "git" failed with exit status 128
  cwd: /mnt/e/Aosp/android-11-r48/.repo/repo
  cmd: ['git', 'fetch', '--quiet', '--progress', 'origin', '+refs/heads/*:refs/remotes/origin/*', '+refs/tags/*:refs/tags/*']
fatal: double check your --repo-rev setting.
fatal: cloning the git-repo repository failed, will remove '.repo/repo'

解决方案

> git config --global https.sslverify false
> git config --global http.sslverify false

As常见问题

Wed, 09 Mar 2022 00:00:00 +0000

AS编译日志乱码

https://www.jianshu.com/p/b8d2e46e13f1

AS快捷键

https://www.cnblogs.com/aashui/p/7657803.html

Dialogfragment

Fri, 04 Mar 2022 00:00:00 +0000

https://www.cnblogs.com/guanxinjing/p/12044196.html

https://developer.android.google.cn/guide/topics/ui/dialogs

https://cloud.tencent.com/developer/article/1893270

https://www.cnblogs.com/cuichen16/p/10785933.html

https://cloud.tencent.com/developer/article/1453726

Android高斯模糊

Fri, 04 Mar 2022 00:00:00 +0000

https://juejin.cn/post/6934591886875164680 https://github.com/wasabeef/Blurry

https://www.jianshu.com/p/02da487a2f43

Android电池电量

Fri, 04 Mar 2022 00:00:00 +0000

https://developer.android.google.cn/training/monitoring-device-state/battery-monitoring?hl=zh-cn

https://developer.android.google.cn/topic/performance/power?hl=zh-cn

Android广播接收器

Fri, 04 Mar 2022 00:00:00 +0000

https://www.li-xyz.com/index.php/archives/2184/

https://www.li-xyz.com/index.php

Alex

Activity启动模式

修改记录

Activity启动模式

标准模式(standard)

声明Activity

栈顶复用模式(singleTop)

栈内复用模式(singleTask)

单例模式(singleInstance)

Kotlin

Learning materials

学习资料

Overview﻿

概述

Basic syntax

基本语法

Package definition and imports

包定义和导入

Program entry point

程序进入点

Print to the standard output﻿

打印到标准输出

Functions

函数

Variables

变量

Creating classes and instances﻿

创建类和实例

Comments

注释

String templates

字符串模板

Conditional expressions﻿

条件表达式

for loop

while loop

when expression

Ranges

范围

Collections

Nullable values and null checks

可空值和空检查

Type checks and automatic casts

类型检查和自动转换

Idioms

Create DTOs (POJOs/POCOs)

Launcher3

Logcat

Aosp源码下载

问题1

解决方案

问题2

解决方案

As常见问题

AS编译日志乱码

AS快捷键

Dialogfragment

Android高斯模糊

Android电池电量

Android广播接收器

Overview

Print to the standard output

Creating classes and instances

Conditional expressions