Java &引用；外部“U目录无法解析或不是字段”；

我正在使用以下教程构建一个签名捕获android应用程序：

但是，我发现了几个错误，说明：

external_dir cannot be resolved or is not a field   CaptureSignature.java   /example/src/com/example/example    line 59 Java Problem
linearLayout cannot be resolved or is not a field   CaptureSignature.java   /example/src/com/example/example    line 67 Java Problem
clear cannot be resolved or is not a field  CaptureSignature.java   /example/src/com/example/example    line 71 Java Problem
getsign cannot be resolved or is not a field    CaptureSignature.java   /example/src/com/example/example    line 72 Java Problem
cancel cannot be resolved or is not a field CaptureSignature.java   /example/src/com/example/example    line 74 Java Problem
yourName cannot be resolved or is not a field   CaptureSignature.java   /example/src/com/example/example    line 77 Java Problem
R cannot be resolved to a variable  CaptureSignatureActivity.java   /example/src/com/example/example    line 21 Java Problem
external_dir cannot be resolved or is not a field   CaptureSignature.java   /example/src/com/example/example    line 57 Java Problem
R cannot be resolved to a variable  CaptureSignatureActivity.java   /example/src/com/example/example    line 19 Java Problem
signature cannot be resolved or is not a field  CaptureSignature.java   /example/src/com/example/example    line 55 Java Problem

…我不知道为什么。（我正在一步一步地学习这个例子）

有什么建议吗

来源：CaptureSignature.java

public class CaptureSignature extends Activity { 

    LinearLayout mContent;
    signature mSignature;
    Button mClear, mGetSign, mCancel;
    public static String tempDir;
    public int count = 1;
    public String current = null;
    private Bitmap mBitmap;
    View mView;
    File mypath;

    private String uniqueId;
    private EditText yourName;

    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.signature);

        tempDir = Environment.getExternalStorageDirectory() + "/" + getResources().getString(R.string.external_dir) + "/";
        ContextWrapper cw = new ContextWrapper(getApplicationContext());
        File directory = cw.getDir(getResources().getString(R.string.external_dir), Context.MODE_PRIVATE);

        prepareDirectory();
        uniqueId = getTodaysDate() + "_" + getCurrentTime() + "_" + Math.random();
        current = uniqueId + ".png";
        mypath= new File(directory,current);


        mContent = (LinearLayout) findViewById(R.id.linearLayout);
        mSignature = new signature(this, null);
        mSignature.setBackgroundColor(Color.WHITE);
        mContent.addView(mSignature, LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
        mClear = (Button)findViewById(R.id.clear);
        mGetSign = (Button)findViewById(R.id.getsign);
        mGetSign.setEnabled(false);
        mCancel = (Button)findViewById(R.id.cancel);
        mView = mContent;

        yourName = (EditText) findViewById(R.id.yourName);

        mClear.setOnClickListener(new OnClickListener() 
        {        
            public void onClick(View v) 
            {
                Log.v("log_tag", "Panel Cleared");
                mSignature.clear();
                mGetSign.setEnabled(false);
            }
        });

        mGetSign.setOnClickListener(new OnClickListener() 
        {        
            public void onClick(View v) 
            {
                Log.v("log_tag", "Panel Saved");
                boolean error = captureSignature();
                if(!error){
                    mView.setDrawingCacheEnabled(true);
                    mSignature.save(mView);
                    Bundle b = new Bundle();
                    b.putString("status", "done");
                    Intent intent = new Intent();
                    intent.putExtras(b);
                    setResult(RESULT_OK,intent);   
                    finish();
                }
            }
        });

        mCancel.setOnClickListener(new OnClickListener() 
        {        
            public void onClick(View v) 
            {
                Log.v("log_tag", "Panel Canceled");
                Bundle b = new Bundle();
                b.putString("status", "cancel");
                Intent intent = new Intent();
                intent.putExtras(b);
                setResult(RESULT_OK,intent);  
                finish();
            }
        });

    }

    @Override
    protected void onDestroy() {
        Log.w("GetSignature", "onDestory");
        super.onDestroy();
    }

    private boolean captureSignature() {

        boolean error = false;
        String errorMessage = "";


        if(yourName.getText().toString().equalsIgnoreCase("")){
            errorMessage = errorMessage + "Please enter your Name\n";
            error = true;
        }   

        if(error){
            Toast toast = Toast.makeText(this, errorMessage, Toast.LENGTH_SHORT);
            toast.setGravity(Gravity.TOP, 105, 50);
            toast.show();
        }

        return error;
    }

    private String getTodaysDate() { 

        final Calendar c = Calendar.getInstance();
        int todaysDate =     (c.get(Calendar.YEAR) * 10000) + 
        ((c.get(Calendar.MONTH) + 1) * 100) + 
        (c.get(Calendar.DAY_OF_MONTH));
        Log.w("DATE:",String.valueOf(todaysDate));
        return(String.valueOf(todaysDate));

    }

    private String getCurrentTime() {

        final Calendar c = Calendar.getInstance();
        int currentTime =     (c.get(Calendar.HOUR_OF_DAY) * 10000) + 
        (c.get(Calendar.MINUTE) * 100) + 
        (c.get(Calendar.SECOND));
        Log.w("TIME:",String.valueOf(currentTime));
        return(String.valueOf(currentTime));

    }


    private boolean prepareDirectory() 
    {
        try
        {
            if (makedirs()) 
            {
                return true;
            } else {
                return false;
            }
        } catch (Exception e) 
        {
            e.printStackTrace();
            Toast.makeText(this, "Could not initiate File System.. Is Sdcard mounted properly?", 1000).show();
            return false;
        }
    }

    private boolean makedirs() 
    {
        File tempdir = new File(tempDir);
        if (!tempdir.exists())
            tempdir.mkdirs();

        if (tempdir.isDirectory()) 
        {
            File[] files = tempdir.listFiles();
            for (File file : files) 
            {
                if (!file.delete()) 
                {
                    System.out.println("Failed to delete " + file);
                }
            }
        }
        return (tempdir.isDirectory());
    }

    public class signature extends View 
    {
        private static final float STROKE_WIDTH = 5f;
        private static final float HALF_STROKE_WIDTH = STROKE_WIDTH / 2;
        private Paint paint = new Paint();
        private Path path = new Path();

        private float lastTouchX;
        private float lastTouchY;
        private final RectF dirtyRect = new RectF();

        public signature(Context context, AttributeSet attrs) 
        {
            super(context, attrs);
            paint.setAntiAlias(true);
            paint.setColor(Color.BLACK);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            paint.setStrokeWidth(STROKE_WIDTH);
        }

        public void save(View v) 
        {
            Log.v("log_tag", "Width: " + v.getWidth());
            Log.v("log_tag", "Height: " + v.getHeight());
            if(mBitmap == null)
            {
                mBitmap =  Bitmap.createBitmap (mContent.getWidth(), mContent.getHeight(), Bitmap.Config.RGB_565);;
            }
            Canvas canvas = new Canvas(mBitmap);
            try
            {
                FileOutputStream mFileOutStream = new FileOutputStream(mypath);

                v.draw(canvas); 
                mBitmap.compress(Bitmap.CompressFormat.PNG, 90, mFileOutStream); 
                mFileOutStream.flush();
                mFileOutStream.close();
                String url = Images.Media.insertImage(getContentResolver(), mBitmap, "title", null);
                Log.v("log_tag","url: " + url);
                //In case you want to delete the file
                //boolean deleted = mypath.delete();
                //Log.v("log_tag","deleted: " + mypath.toString() + deleted);
                //If you want to convert the image to string use base64 converter

            }
            catch(Exception e) 
            { 
                Log.v("log_tag", e.toString()); 
            } 
        }

        public void clear() 
        {
            path.reset();
            invalidate();
        }

        @Override
        protected void onDraw(Canvas canvas) 
        {
            canvas.drawPath(path, paint);
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) 
        {
            float eventX = event.getX();
            float eventY = event.getY();
            mGetSign.setEnabled(true);

            switch (event.getAction()) 
            {
            case MotionEvent.ACTION_DOWN:
                path.moveTo(eventX, eventY);
                lastTouchX = eventX;
                lastTouchY = eventY;
                return true;

            case MotionEvent.ACTION_MOVE:

            case MotionEvent.ACTION_UP:

                resetDirtyRect(eventX, eventY);
                int historySize = event.getHistorySize();
                for (int i = 0; i < historySize; i++) 
                {
                    float historicalX = event.getHistoricalX(i);
                    float historicalY = event.getHistoricalY(i);
                    expandDirtyRect(historicalX, historicalY);
                    path.lineTo(historicalX, historicalY);
                }
                path.lineTo(eventX, eventY);
                break;

            default:
                debug("Ignored touch event: " + event.toString());
                return false;
            }

            invalidate((int) (dirtyRect.left - HALF_STROKE_WIDTH),
                    (int) (dirtyRect.top - HALF_STROKE_WIDTH),
                    (int) (dirtyRect.right + HALF_STROKE_WIDTH),
                    (int) (dirtyRect.bottom + HALF_STROKE_WIDTH));

            lastTouchX = eventX;
            lastTouchY = eventY;

            return true;
        }

        private void debug(String string){
        }

        private void expandDirtyRect(float historicalX, float historicalY) 
        {
            if (historicalX < dirtyRect.left) 
            {
                dirtyRect.left = historicalX;
            } 
            else if (historicalX > dirtyRect.right) 
            {
                dirtyRect.right = historicalX;
            }

            if (historicalY < dirtyRect.top) 
            {
                dirtyRect.top = historicalY;
            } 
            else if (historicalY > dirtyRect.bottom) 
            {
                dirtyRect.bottom = historicalY;
            }
        }

        private void resetDirtyRect(float eventX, float eventY) 
        {
            dirtyRect.left = Math.min(lastTouchX, eventX);
            dirtyRect.right = Math.max(lastTouchX, eventX);
            dirtyRect.top = Math.min(lastTouchY, eventY);
            dirtyRect.bottom = Math.max(lastTouchY, eventY);
        }
    }
}

舱单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.as400samplecode" android:versionCode="1"
    android:versionName="1.0">
    <uses-sdk android:minSdkVersion="10" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application android:icon="@drawable/icon" android:label="@string/app_name"
        android:theme="@android:style/Theme.Light">
        <activity android:name=".CaptureSignatureActivity"
            android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".CaptureSignature" android:label="Signature Confirmation"
            android:theme="@android:style/Theme.Dialog" />
    </application>
</manifest>

字符串：

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="hello">Hello World, CaptureSignatureActivity!</string>
    <string name="app_name">CaptureSignature</string>
    <string name="external_dir">GetSignature</string>
</resources>

世界你好，CaptureSignatureActivity！
捕获签名
获取签名

您的strings.xml文件中似乎缺少一些字符串显示导入语句。有机会导入android.R；是-我正在导入android.r可能缺少哪些字符串？我直接从示例中复制：我很确定示例中没有丢失字符串。。。（我完全复制了它——根据这里的评论，似乎没有其他人对缺少字符串有问题：）

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="hello">Hello World, CaptureSignatureActivity!</string>
    <string name="app_name">CaptureSignature</string>
    <string name="external_dir">GetSignature</string>
</resources>