在 android 中写入文本文件

Question

我试过代码 , 但它对我不起作用:-(。我几乎没有用一个 textViev "pokusnejText".

将它重写为我的基本 Android Studio 项目，空 activity

这是我的代码 MainActivity.kt:

package com.example.zapisdosouboru

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.os.Environment
import android.widget.TextView
import java.io.File
import java.io.PrintWriter

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val pokusnejText = findViewById<TextView>(R.id.pokusnejText)


        var answer : String = ""
        val sd_main = File(Environment.getExternalStorageDirectory().toString() + "/smazat" )
        var success = true
        if (!sd_main.exists()) {
            success = sd_main.mkdir()
            if (success) {
                answer = "folder created"
            } else {
                answer = "folder can not be created"
            }
        }

        if (success) {
            val sd = File("testingFile.txt")

            if (!sd.exists()) {
                success = sd.mkdir()
            }

            if (success) {
                // directory exists or already created
                val dest = File(sd, "testingFile.txt")

                try {
                    // response is the data written to file
                    PrintWriter(dest).use { out -> out.println(answer) }
                    answer = "writed to" + sd.toString()
                } catch (e: Exception) {
                    answer = "can not be written"
                }

            } else {
                answer = "folder or file does not exists"
            }
        }
        pokusnejText.text = answer
    }
}

这是我的 AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.example.zapisdosouboru">
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <application
            android:allowBackup="true"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

    </application>

</manifest>

首先我重写的是

val sd_main = File(Environment.getExternalStorageDirectory()+"/yourlocation")

到

val sd_main = File(Environment.getExternalStorageDirectory().toString() + "/yourlocation" )

因为没有 toString() 被加号标记为红色 ... 但它仍然不起作用并回答说它无法创建文件夹... 我已经在 Android Studio 模拟器中用 android 6.0

试过了

一些补充问题：我对代码中一次使用一个参数而第二次使用两个参数的函数 File() 感到非常困惑。 Kotlin 是否存在一些类似的网页 http://www.cplusplus.com/ - 我找不到任何对 c++ 如此有用的网页。

感谢帮助 fik236

Answer 1

你是说你在 Android 的模拟器上试过了 6. 在写入外部存储之前你是否 explicitly ask 获得 WRITE_EXTERNAL_STORAGE 许可？这段代码执行时 logcat 中的输出是什么？应该在那里说它无法创建文件，因为 'permission denied'

关于类似于 cplusplus.com 的站点，当然，有 Kotlin language reference 具有与 cpp.com 相同的功能，而且我认为它更好，因为它包含对书籍的引用、在线课程等

Answer 2

感谢 Maroš Šeleng 我有了一些工作代码。在这里：

package com.example.zapisdosouboru

import android.Manifest
import android.content.pm.PackageManager
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.os.Environment
import android.support.v4.app.ActivityCompat
import android.widget.TextView
import java.io.File
import java.io.PrintWriter

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)



        // Here, thisActivity is the current activity
        if (checkSelfPermission( Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {

            // Permission is not granted
            // Should we show an explanation?
            if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
                // Show an explanation to the user *asynchronously* -- don't block
                // this thread waiting for the user's response! After the user
                // sees the explanation, try again to request the permission.
            } else {
                // No explanation needed, we can request the permission.
                ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE), 1)

                // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
                // app-defined int constant. The callback method gets the
                // result of the request.
            }
        } else {
            // Permission has already been granted
        }

        val pokusnejText = findViewById<TextView>(R.id.pokusnejText)


        var answer : String = ""
        val sd_main = File(Environment.getExternalStorageDirectory() , "smazat" )
        var success = true
        if (!sd_main.exists()) {
            success = sd_main.mkdir()
            if (success) {
                answer = "folder created"
            } else {
                answer = "folder can not be created"
            }
        }

        if (success) {
            val sd = File(sd_main,"testingFile.txt")

            if (!sd.isFile()) {
                success = sd.createNewFile()
            }

            if (success) {
                // directory exists or already created

                try {
                    answer = "writed to" + sd.toString()
                    PrintWriter(sd).use { out -> out.println("testing text") }

                } catch (e: Exception) {
                    answer = "can not be written"
                }

            } else {
                answer = "folder or file does not exists"
            }
        }
        pokusnejText.text = answer
    }
}

在 android 中写入文本文件

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