因为需要后台默认截图，所以特意搜了这个，然后做了一个这样的DEMO.

第一个方法：（此方法只适用于Activity.不能截取应用外的界面）代码很少，这有这一段：

 
 
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
 
import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.os.Environment;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
 
@SuppressLint("SetJavaScriptEnabled")
public class MainActivity extends Activity {
 
	private Button leftStepBtn ;
	private Bitmap bm;
	private String imgurl;
 
	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		imgurl = Environment.getExternalStorageDirectory()
				.getPath() + "/DCIM/MyPicture/"; 
 
		leftStepBtn = (Button) findViewById(R.id.leftStepBtn);
		leftStepBtn.setVisibility(View.VISIBLE);
		leftStepBtn.setText("截屏");
		leftStepBtn.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				// 得到当前view所在view结构中的根view
				View vv = v.getRootView();
				// 设置属性
				vv.setDrawingCacheEnabled(true);
				// 取得位图
				bm = vv.getDrawingCache();
				showConfirmDialog(1).show();
			}
		});
	}
 
	@SuppressLint("SdCardPath")
	public void saveBitmap(Bitmap bitmap, String bitName) throws IOException {
		File folder = new File(imgurl);
		if (!folder.exists()) {
			folder.mkdir();
		}
		File file = new File(imgurl + bitName + ".jpg");
		Toast.makeText(MainActivity.this, "保存图片中", Toast.LENGTH_SHORT).show();
		FileOutputStream out;
		if (!file.exists()) {
 
			try {
				out = new FileOutputStream(file);
				if (bitmap.compress(Bitmap.CompressFormat.PNG, 70, out)) {
					Toast.makeText(MainActivity.this, "成功存入相册",
							Toast.LENGTH_SHORT).show();
					out.flush();
					out.close();
				}
			} catch (FileNotFoundException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
 
	/**
	 * 确定保存 AlertDialog
	 * @param i 
	 */
	public AlertDialog showConfirmDialog(final int i) {
		return new AlertDialog.Builder(MainActivity.this)
				.setIcon(android.R.drawable.progress_horizontal)
				.setTitle("确认保存").setMessage("请确认是否保存图片!")
				.setPositiveButton("确定", new DialogInterface.OnClickListener() {
 
					@Override
					public void onClick(DialogInterface dialog, int which) {
						// TODO Auto-generated method stub
						try {
							if(i == 1){
								String num = getRandomCode();
								saveBitmap(bm, "imagePic" + num);
							} 
						} catch (IOException e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
						}
					}
				}).setNegativeButton("取消", null).create();
	}
 
	// 随机获取图片编号
	private String getRandomCode() {
		String num = "";
		for (int i = 0; i < 10; i++) {
			int f = (int) (Math.random() * 10);
			num += f;
		}
		return num;
	}
 
	// 按钮
	@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {
		if (keyCode == KeyEvent.KEYCODE_BACK) {
			finish();
			return true;
		}
		return false;
	}
 
}

第二个方法（此方法可以截取应用外的屏幕，即桌面或其他应用）：

 String imgurl = Environment.getExternalStorageDirectory()
				.getPath() + "/DCIM/MyPicture/"; 
	 SimpleDateFormat format = new SimpleDateFormat("yyyy.MM.dd_HH.mm.ss");
		Date date = Calendar.getInstance().getTime();
		String timeStamp = format.format(date);
		String fullPath = imgurl + timeStamp +".png" ;
		ScreentShotUtil.getInstance().takeScreenshot(context,fullPath);

ScreentShotUtil为一个shell命令的封装=-=如果你的机器不能用shell命令，可以放弃这个方法。