Question

我想将应用程序资产文件夹中的一个非常大的目录复制到应用程序第一次运行的数据文件夹中。我怎么做？我已经尝试了一些例子，但没有任何效果，所以我没有任何东西。我的目标是Android 4.2。

谢谢， Yannik

Answer 1

尝试使用Application实例的代码（您应该在清单中编写类）：此代码将assets / files文件夹的内容复制到app的缓存文件夹中（您可以在copyAssetFolder（）函数中放置其他路径）。仅在第一次启动App时

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.app.Application;
import android.content.Context;
import android.content.res.AssetManager;
import android.preference.PreferenceManager;

public class MyApplication extends Application {
    private static Context  s_sharedContext;

    @Override
    public void onCreate () {
        super.onCreate();   
        if (!PreferenceManager.getDefaultSharedPreferences(
                getApplicationContext())
            .getBoolean("installed", false)) {
            PreferenceManager.getDefaultSharedPreferences(
                    getApplicationContext())
                .edit().putBoolean("installed", true).commit();

            copyAssetFolder(getAssets(), "files", 
                    "/data/data/com.example.appname/files");
        }
    }

    private static boolean copyAssetFolder(AssetManager assetManager,
            String fromAssetPath, String toPath) {
        try {
            String[] files = assetManager.list(fromAssetPath);
            new File(toPath).mkdirs();
            boolean res = true;
            for (String file : files)
                if (file.contains("."))
                    res &= copyAsset(assetManager, 
                            fromAssetPath + "/" + file,
                            toPath + "/" + file);
                else 
                    res &= copyAssetFolder(assetManager, 
                            fromAssetPath + "/" + file,
                            toPath + "/" + file);
            return res;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

    private static boolean copyAsset(AssetManager assetManager,
            String fromAssetPath, String toPath) {
        InputStream in = null;
        OutputStream out = null;
        try {
          in = assetManager.open(fromAssetPath);
          new File(toPath).createNewFile();
          out = new FileOutputStream(toPath);
          copyFile(in, out);
          in.close();
          in = null;
          out.flush();
          out.close();
          out = null;
          return true;
        } catch(Exception e) {
            e.printStackTrace();
            return false;
        }
    }

    private static void copyFile(InputStream in, OutputStream out) throws IOException {
        byte[] buffer = new byte[1024];
        int read;
        while((read = in.read(buffer)) != -1){
          out.write(buffer, 0, read);
        }
    }

}

Answer 2

private fun copyAssets(
    assetManager: AssetManager,
    assetPath: String,
    outputPath: String
) {
    // check if asset path is a file. if file exists, then it is copied to the output path
    try {
        // throws IOException when file does not exist
        val assetFd = assetManager.openFd(assetPath)
        // file exists, so file is copied to the output path
        copyFile(assetFd, outputPath)
    } catch (e: Exception) {
        try {
            // file does not exist
            // try to list asset path content
            val files = assetManager.list(assetPath)
            // create output directory if not exist
            val outputDir = File(outputPath)
            outputDir.mkdirs()
            // loop through asset path directory and copy content recursively
            files?.forEach { file ->
                // new asset path is set to file
                val newAssetPath = "$assetPath/$file"
                // set relative output file path
                val newOutputPath = "$outputPath/$file"
                // recursively copy from asset path to the output path
                copyAssets(assetManager, newAssetPath, newOutputPath)
            }
        } catch (e: java.lang.Exception) {
            // asset path is neither a file nor a directory
            throw IOException("asset path does not exist")
        }
    }
}

/**
 * copy file from asset file descriptor to the output file path
 */
private fun copyFile(inputFd: AssetFileDescriptor, outputFilePath: String) {
    val inputStream = inputFd.createInputStream()
    val outputStream = FileOutputStream(outputFilePath)
    val buffer = ByteArray(8192)
    var read = inputStream.read(buffer)
    while (read != -1) {
        outputStream.write(buffer, 0, read)
        read = inputStream.read(buffer)
    }
    inputStream.close()
    outputStream.close()
}

一个目录可以通过以下方式从assets复制到data目录

val assetPath = "resources"
val outputPath = "${appContext.filesDir.absolutePath}/resources"
val assetManager = appContext.resources.assets
copyAssets(assetManager, assetPath, outputPath)

将目录从资产复制到数据文件夹

2 个答案: