getAssets()方法将在Activity类内部调用时工作。

如果你在非Activity类中调用这个方法，那么你需要从Context中调用这个方法，这个Context是从Activity类中传递过来的。下面是可以访问该方法的行。

ContextInstance.getAssets();

ContextInstance可以作为Activity类的this传递。

AssetManager assetManager = getAssets();
InputStream inputStream = null;
try {
    inputStream = assetManager.open("helloworld.txt");
}
catch (IOException e){
    Log.e("message: ",e.getMessage());
}

下面是一个在资产中读取文件的方法:

/**
 * Reads the text of an asset. Should not be run on the UI thread.
 * 
 * @param mgr
 *            The {@link AssetManager} obtained via {@link Context#getAssets()}
 * @param path
 *            The path to the asset.
 * @return The plain text of the asset
 */
public static String readAsset(AssetManager mgr, String path) {
    String contents = "";
    InputStream is = null;
    BufferedReader reader = null;
    try {
        is = mgr.open(path);
        reader = new BufferedReader(new InputStreamReader(is));
        contents = reader.readLine();
        String line = null;
        while ((line = reader.readLine()) != null) {
            contents += '\n' + line;
        }
    } catch (final Exception e) {
        e.printStackTrace();
    } finally {
        if (is != null) {
            try {
                is.close();
            } catch (IOException ignored) {
            }
        }
        if (reader != null) {
            try {
                reader.close();
            } catch (IOException ignored) {
            }
        }
    }
    return contents;
}

ExceptionProof

It maybe too late but for the sake of others who look for the peachy answers.

loadAssetFile()方法返回资产的纯文本，如果有任何错误，则返回defaultValue参数。

public static String loadAssetFile(Context context, String fileName, String defaultValue) {
    String result=defaultValue;
    InputStreamReader inputStream=null;
    BufferedReader bufferedReader=null;
    try {
        inputStream = new InputStreamReader(context.getAssets().open(fileName));
        bufferedReader = new BufferedReader(inputStream);
        StringBuilder out= new StringBuilder();
        String line = bufferedReader.readLine();
        while (line != null) {
            out.append(line);
            line = bufferedReader.readLine();
        }
        result=out.toString();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            Objects.requireNonNull(inputStream).close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            Objects.requireNonNull(bufferedReader).close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    return result;
}

在MainActivity.java

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tvView = (TextView) findViewById(R.id.tvView);

        AssetsReader assetsReader = new AssetsReader(this);
        if(assetsReader.getTxtFile(your_file_title)) != null)
        {
            tvView.setText(assetsReader.getTxtFile(your_file_title)));
        }
    }

此外，您还可以创建单独的类来完成所有工作

public class AssetsReader implements Readable{

    private static final String TAG = "AssetsReader";


    private AssetManager mAssetManager;
    private Activity mActivity;

    public AssetsReader(Activity activity) {
        this.mActivity = activity;
        mAssetManager = mActivity.getAssets();
    }

    @Override
    public String getTxtFile(String fileName)
    {
        BufferedReader reader = null;
        InputStream inputStream = null;
        StringBuilder builder = new StringBuilder();

        try{
            inputStream = mAssetManager.open(fileName);
            reader = new BufferedReader(new InputStreamReader(inputStream));

            String line;

            while((line = reader.readLine()) != null)
            {
                Log.i(TAG, line);
                builder.append(line);
                builder.append("\n");
            }
        } catch (IOException ioe){
            ioe.printStackTrace();
        } finally {

            if(inputStream != null)
            {
                try {
                    inputStream.close();
                } catch (IOException ioe){
                    ioe.printStackTrace();
                }
            }

            if(reader != null)
            {
                try {
                    reader.close();
                } catch (IOException ioe)
                {
                    ioe.printStackTrace();
                }
            }
        }
        Log.i(TAG, "builder.toString(): " + builder.toString());
        return builder.toString();
    }
}

在我看来，最好创建一个界面，但这不是必要的

public interface Readable {
    /**
     * Reads txt file from assets
     * @param fileName
     * @return string
     */
    String getTxtFile(String fileName);
}

getAssets()

它只适用于其他任何类的活动，你必须为它使用上下文。

让Utils类的构造函数将活动引用(丑陋的方式)或应用程序上下文作为参数传递给它。在Utils类中使用getAsset()。