在開發中需要引用程序資源,比如項目中assets和res目錄下的圖片、layout、values等或者需要系統內置的資源。
資源分爲兩種:
第一種:res目錄下的資源(不會被編譯,但是會生成id)
第二種:assets文件夾下的資源文件,又叫原始資源文件(不會被編譯,也不會生成id)
1、創建Assets文件夾
右鍵目標文件夾進行創建
2、獲取Assets文件夾的管理類
AssetManager assets = getAssets();
3、遍歷文件夾下的資源列表
String[] list = assets.list();
在app/src/main/java/lwplw.com.helloworld/FileUtils.java
文件中有:
String fileNames[] = context.getAssets().list(srcPath);
這句就相當於一次實現了上面的2和3。
4、獲取Assets文件夾的資源
5、示例程序
package lwplw.com.helloworld;
import android.content.Context;
import android.os.Environment;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
public class FileUtils {
private static FileUtils instance;
private static final int SUCCESS = 1;
private static final int FAILED = 0;
private Context context;
private FileOperateCallback callback;
private volatile boolean isSuccess;
private String errorStr;
public static FileUtils getInstance(Context context) {
if (instance == null)
instance = new FileUtils(context);
return instance;
}
private FileUtils(Context context) {
this.context = context;
}
private Handler handler = new Handler(Looper.getMainLooper()) {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if (callback != null) {
if (msg.what == SUCCESS) {
callback.onSuccess();
}
if (msg.what == FAILED) {
callback.onFailed(msg.obj.toString());
}
}
}
};
public FileUtils copyAssetsToSD(final String srcPath, final String sdPath) {
new Thread(new Runnable() {
@Override
public void run() {
copyAssetsToDst(context, srcPath, sdPath);
if (isSuccess)
handler.obtainMessage(SUCCESS).sendToTarget();
else
handler.obtainMessage(FAILED, errorStr).sendToTarget();
}
}).start();
return this;
}
public void setFileOperateCallback(FileOperateCallback callback) {
this.callback = callback;
}
private void copyAssetsToDst(Context context, String srcPath, String dstPath) {
try {
String fileNames[] = context.getAssets().list(srcPath);
if (fileNames.length > 0) {
File file = new File(Environment.getExternalStorageDirectory(), dstPath);
if (!file.exists()) file.mkdirs();
for (String fileName : fileNames) {
if (!srcPath.equals("")) { // assets 文件夾下的目錄
copyAssetsToDst(context, srcPath + File.separator + fileName, dstPath + File.separator + fileName);
} else { // assets 文件夾
copyAssetsToDst(context, fileName, dstPath + File.separator + fileName);
}
}
} else {
File outFile = new File(Environment.getExternalStorageDirectory(), dstPath);
InputStream is = context.getAssets().open(srcPath);
FileOutputStream fos = new FileOutputStream(outFile);
byte[] buffer = new byte[1024];
int byteCount;
while ((byteCount = is.read(buffer)) != -1) {
fos.write(buffer, 0, byteCount);
}
fos.flush();
is.close();
fos.close();
}
isSuccess = true;
} catch (Exception e) {
e.printStackTrace();
errorStr = e.getMessage();
isSuccess = false;
}
}
public interface FileOperateCallback {
void onSuccess();
void onFailed(String error);
}
}
6、使用舉例
見app/src/main/java/lwplw.com.helloworld/MainActivity.java
文件
函數功能:
(1)在手機存儲卡創建目錄結構lwplw_helloworld/data
(2)把assets文件夾中的資源,全部copy倒sd卡lwplw_helloworld/data目錄
7、注意事項
(1)assets文件是壓縮在apk中的,apk運行時無法直接訪問該目錄,需要copy出來。
(2)需要等到assets文件中資源全部copy完成後,回調到 onSuccess(),再執行後續操作。