双击back退出app.md

双击back返回键退出app功能的实现方式

有两种实现思路，看个人喜好吧：

方式1：

public class MainActivity extends Activity {

	private Toast toast;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		toast = Toast.makeText(getApplicationContext(), "确定退出？", 0);
	}

	public void onBackPressed() {
		quitToast();
	}

	private void quitToast() {
		if(null == toast.getView().getParent()) {
			toast.show();
		}else{
			System.exit(0);
		}
	}
}

方式2：

public class MainActivity extends Activity {

	private Toast toast;
	rotected void onCreate(Bundle savedInstanceState) {
	 	...
	         toast = Toast.makeText(this, "再按一次退出应用", Toast.LENGTH_SHORT);
	        toast.setGravity(Gravity.BOTTOM, 0, ConversionUtil.dip2px(this, 150));
	}

	@Override 
	public void onBackPressed() { 
	    if (doubleBackToExitPressedOnce) { 
	        if(toast!=null){
	            toast.cancel();
	        }
	        super.onBackPressed(); 
	        return; 
	    } 
	 
	    this.doubleBackToExitPressedOnce = true;
	    toast.show();
	 
	    new Handler().postDelayed(new Runnable() {
	 
	        @Override 
	        public void run() { 
	            doubleBackToExitPressedOnce=false;                        
	        } 
	    }, 2000); 
	} 
}