浅谈Android手写画板(个性签名)示例及遇到的一些问题

下面我们来写一个自定义可以触控屏幕绘制线条的View；

package com.signaturedemo.view;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Path;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;public class SignatureView extends View {    private Paint mPaint = new Paint();    private Path mPath = new Path();    public SignatureView(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        // TODO Auto-generated constructor stub        init();    }    public SignatureView(Context context, AttributeSet attrs) {        super(context, attrs);        // TODO Auto-generated constructor stub        init();    }    public SignatureView(Context context) {        super(context);        // TODO Auto-generated constructor stub        init();    }    private void init() {        mPaint.setAntiAlias(true);        mPaint.setColor(Color.BLACK);        mPaint.setStyle(Paint.Style.STROKE);        mPaint.setStrokeJoin(Paint.Join.ROUND);        mPaint.setStrokeWidth(5f);    }    @Override    protected void onDraw(Canvas canvas) {        // TODO Auto-generated method stub        canvas.drawPath(mPath, mPaint);    }    private float cur_x, cur_y;    @Override    public boolean onTouchEvent(MotionEvent event) {        // TODO Auto-generated method stub        float eventX = event.getX();        float eventY = event.getY();        switch (event.getAction()) {        case MotionEvent.ACTION_DOWN:            cur_x = eventX;            cur_y = eventY;            mPath.moveTo(eventX, eventY);            return true;        case MotionEvent.ACTION_MOVE:        case MotionEvent.ACTION_UP:            myDraw(event); //减锯齿描绘            mPath.quadTo(cur_x, cur_y, eventX, eventY);            cur_x = eventX;            cur_y = eventY;            break;        default:            return false;        }        invalidate();        return true;    }    /**     * 绘图时减锯齿操作     * @param event     */    private void myDraw(MotionEvent event) {        int historySize = event.getHistorySize();        for(int i=0; i<historySize; i++) {            float historicalX = event.getHistoricalX(i);            float historicalY = event.getHistoricalY(i);            mPath.quadTo(cur_x, cur_y, historicalX, historicalY);        }    }    /**     * 清除描绘     */    public void clear() {        mPath.reset();        invalidate();    }}

上面就完成了一个自定义画板的View，然后在布xml文件中引用View即可；

    <com.signaturedemo.view.SignatureView        android:id="@+id/view_signature"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:background="@color/white" />

接下来可能我们就想要保存写好的个性签名图片，重点就来了！这就涉及到如何讲一个View视图生成一个图片对象（Bitmap）呢？一般有两种方法：
第一种

/*** view_signature为我们要保存成图片的View*/        view_signature.setDrawingCacheEnabled(true);        view_signature.measure(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED),                MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));        view_signature.layout(0, 0, view_signature.getMeasuredWidth(), view_signature.getMeasuredHeight());        view_signature.buildDrawingCache();        Bitmap bmp = view_signature.getDrawingCache(); 

这种方法我用了，不知是哪里的问题，得到的Bitmap对象为null，按照网上查找的方法就是这样写的。还是得到null，有知道的涉及到的望告知一下；

第二种， 这种就是我现在用的，可以很方便的把View视图转成Bitmap对象了。贴代码

Bitmap bmp = Bitmap.createBitmap(view_signature.getMeasuredWidth(), view_signature.getMeasuredHeight(), Config.ARGB_8888);        view_signature.draw(new Canvas(bmp));

大功告成了一半，那接下来就要存入本地咯。

/**     * 保存签名文件图片     * @param bmp Bitmap图片对象     * @param path 保存的路径     */    public void creatBitmapFile(Bitmap bmp, String path) {        try {            File file = new File(mPath); //定义好mPath存的路径            if(!file.exists()) { //判断文件夹是否存在，不存在则创建                file.mkdir();            }            file = new File(path);            if(!file.exists()) {                file.createNewFile();            }            FileOutputStream fileOut = new FileOutputStream(file);            bmp.compress(Bitmap.CompressFormat.PNG, 100, fileOut);            fileOut.flush();            fileOut.close();            updatePhotos(file); //更新图库            Toast.makeText(this, R.string.msg_save_succ, Toast.LENGTH_SHORT).show();        } catch (FileNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();            Log.e("creatBitmapFile", e.getMessage());        } catch (IOException e) {            // TODO Auto-generated catch block            Log.e("creatBitmapFile", e.getMessage());            e.printStackTrace();        } finally {        }    }    /**     * 打开图库     */    private void scanPicture() {        Intent it_gallery = new Intent();        it_gallery.addCategory(Intent.CATEGORY_OPENABLE);        it_gallery.setType("image/*");        startActivity(it_gallery);    }     /**     * 发送广播，图库更新照片     * @param file 新增的图片     */    private void updatePhotos(File file) {        Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);        Uri uri = Uri.fromFile(file);        intent.setData(uri);        sendBroadcast(intent);    }

好了，成功保存签名的View视图文件。AndroidManifest.xml别忘了加上读写sd卡的权限

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

大功终告成，附个效果截图吧