android中处理写文件

添加读写外部存储的权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

动态权限检查

使用的这个库：
https://github.com/Karumi/Dexter
还是挺方便的。
添加依赖

implementation 'com.karumi:dexter:5.0.0'

需要申请权限的地方：

Dexter.withActivity(getActivity())
      .withPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
      .withListener(new PermissionListener() {
        @Override
        public void onPermissionGranted(PermissionGrantedResponse response) {
          showProgressDialog();
          EventBus.getDefault().post(exportEvent);
        }

        @Override
        public void onPermissionDenied(PermissionDeniedResponse response) {
          Toast.makeText(getContext(), "请打开读写文件权限", Toast.LENGTH_LONG).show();
        }

        @Override
        public void onPermissionRationaleShouldBeShown(PermissionRequest permission, PermissionToken token) {/* ... */}
      }).check();

获取文件路径

  public String getFilePath() {
    File root = android.os.Environment.getExternalStorageDirectory();
    File dir = new File(root.getAbsolutePath(), "download");
    dir.mkdirs();
    return dir.getAbsolutePath();
  }

写文件

  public void writeToSDFile(String coinType, List<AddressPair> data, String fileName) throws IOException {
    FileOutputStream f = null;
    try {
      File file = new File(fileName);
      f = new FileOutputStream(file);
      PrintWriter pw = new PrintWriter(f);
      for (int i = 0; i < data.size(); i++) {
        AddressPair pp = data.get(i);
        pw.println(coinType + "," + pp.address);
      }
      pw.flush();
      pw.close();
    } finally {
      if (f != null) {
        f.close();
      }
    }
  }