如何将 LinearLayout 转换为图像？

Question

我尝试使用以下代码将LinearLayout 转换为图像：

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    LinearLayout lyt = (LinearLayout) findViewById(R.id.lyt);
    lyt.setDrawingCacheEnabled(true);
    lyt.buildDrawingCache(true);

    Bitmap b = Bitmap.createBitmap(lyt.getDrawingCache());

    ImageView img = (ImageView) findViewById(R.id.imageView1);
    img.setImageBitmap(b);

}

但我收到了NullPointerException：

Bitmap b = Bitmap.createBitmap(lyt.getDrawingCache());

布局 XML 的位置：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >


    <LinearLayout
        android:id="@+id/lyt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button 1" />

        <Button
            android:id="@+id/button3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button 2" />

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button 3" />

    </LinearLayout>

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />

</LinearLayout>

Answer 1

试试下面的代码，它可以工作

在清单中添加以下权限

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

MainActivity.java

    public class MainActivity extends Activity implements OnClickListener{
    private LinearLayout linearLayout;
    private Button saveBtn;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        linearLayout = (LinearLayout) findViewById(R.id.linearLayout_view);
        saveBtn = (Button) findViewById(R.id.save_btn);
        saveBtn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        int id = v.getId();
        switch (id) {
        case R.id.save_btn:
            File file = saveBitMap(this, linearLayout);    //which view you want to pass that view as parameter
            if (file != null) {
                Log.i("TAG", "Drawing saved to the gallery!");
            } else {
                Log.i("TAG", "Oops! Image could not be saved.");
            }
            break;
        default:
            break;
        }

    private File saveBitMap(Context context, View drawView){
        File pictureFileDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),"Handcare");
        if (!pictureFileDir.exists()) {
            boolean isDirectoryCreated = pictureFileDir.mkdirs();
            if(!isDirectoryCreated)
                Log.i("ATG", "Can't create directory to save the image");
            return null;
        }
        String filename = pictureFileDir.getPath() +File.separator+ System.currentTimeMillis()+".jpg";
        File pictureFile = new File(filename);
        Bitmap bitmap =getBitmapFromView(drawView);
        try {
            pictureFile.createNewFile();
            FileOutputStream oStream = new FileOutputStream(pictureFile);
            bitmap.compress(CompressFormat.PNG, 100, oStream);
            oStream.flush();
            oStream.close();
        } catch (IOException e) {
            e.printStackTrace();
            Log.i("TAG", "There was an issue saving the image.");
        }       
            scanGallery( context,pictureFile.getAbsolutePath());
        return pictureFile;
    }
    //create bitmap from view and returns it
    private Bitmap getBitmapFromView(View view) {
        //Define a bitmap with the same size as the view
        Bitmap returnedBitmap = Bitmap.createBitmap(view.getWidth(), view.getHeight(),Bitmap.Config.ARGB_8888);
        //Bind a canvas to it
        Canvas canvas = new Canvas(returnedBitmap);
        //Get the view's background
        Drawable bgDrawable =view.getBackground();
        if (bgDrawable!=null) {
            //has background drawable, then draw it on the canvas
            bgDrawable.draw(canvas);
        }   else{
            //does not have background drawable, then draw white background on the canvas
            canvas.drawColor(Color.WHITE);
        }
        // draw the view on the canvas
        view.draw(canvas);
        //return the bitmap
        return returnedBitmap;
    }
    // used for scanning gallery
    private void scanGallery(Context cntx, String path) {
        try {
            MediaScannerConnection.scanFile(cntx, new String[] { path },null, new MediaScannerConnection.OnScanCompletedListener() {
                public void onScanCompleted(String path, Uri uri) {
                }
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Answer 2

我的猜测是您正在 onCreate 中执行该代码。问题在于视图尚未布局。调用 lyt.measure 或稍后调用代码。例如：调用 super.onLayout() 后到 onSizeChanged() 或 onLayout()。

Answer 3

Bitmap b = Bitmap.createBitmap(lyt.getDrawingCache());

该行中唯一可以是null 的是lyt，其余的不能。您可能尚未设置布局，在这种情况下，findViewById() 将返回 null。

您必须先执行setContentView()，然后才能执行findViewById()

Answer 4

以下是将xml布局转换为位图图像的代码片段

private Bitmap convertLayoutToImage() {
        LinearLayout linearView = (LinearLayout) this.getLayoutInflater(null).inflate(R.layout
                .marker_layout, null, false); //you can pass your xml layout

        linearView.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
                View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
        linearView.layout(0, 0, linearView.getMeasuredWidth(), linearView.getMeasuredHeight());

        linearView.setDrawingCacheEnabled(true);
        linearView.buildDrawingCache();
        return linearView.getDrawingCache();// creates bitmap and returns the same
    }

Answer 5

看看对你有没有帮助：

Converting Views to Bitmap Images in Android