Callback2.0

時間 2019-11-11

標籤 callback2.0 callback 简体版

原文原文鏈接

Callback定義？java

a callback is a piece of executable code that is passed as an argument to other code, which is expected to call back (execute) the argument at some convenient time.android

The invocation may be immediate as in a synchronous callback or it might happen at later time, as in an asynchronous callback.設計模式

In all cases, the intention is to specify a function or subroutine as an entity that is, depending on the language, more or less similar to a variable.app

不難看出callback是在一個Class中把一段代碼以argument的形式發送到另一個class中調用。less

咱們在android中常常用onClickListnere的Onclick()這就是一個回調方法。學過js的人應該很明白callback由於js基本都是用callback的。async

Callback實例1

//聲明一個接口  
public interface ICallBack {  
    void postExec();  
}  
//另一個類有方法裏面有個參數以是這個接口類型的  
public class FooBar {  
    private ICallBack callBack;  
    public void setCallBack(ICallBack callBack) {  
        this.callBack = callBack;  
    }  
    public void doSth() {  
        callBack.postExec();  
    }  
}

FooBar中接收一個實現callback方法類而後調用doSth()方法時調用對用的callback方法，而後真正實現callback方法的類中就會觸發並執行callback方法中的代碼。ide

public class Test {  
    public static void main(String[] args) {  
        FooBar foo = new FooBar();  
        foo.setCallBack(new ICallBack() {  
            public void postExec() {  
                System.out.println("method executed.");  
            }  
        });  
        foo.doSth();//調用函數  
    }  
}

在Test，經過FooBar的setCallBack方法以參數的形式把callback方法實現類傳遞給FooBar，當調用foo.doSth();會觸發callback()方法。函數

Callback實例2

學過設計模式的mvp的人應該知道callback怎麼實現的。 MVP中M是具體操做類能夠理解爲操做DB。V是有關GUI的即View那個中間指揮者就是P。post

好比說登陸login。經過V咱們會獲取到帳號密碼，而後再M中驗證數據帳號密碼是否匹配，而後從新回到V中更新UI。fetch

package com.amap.login;

import android.content.Context;

public interface ILoginModel {
	void login(String userid, String password, Context context, OnLoginFinishedListener listener);
}

package com.amap.login;

import android.content.Context;

public interface ILoginPresenter {
	
	void validateCredentials(String userid, String password, Context context);
	void onDestroy();
	
}

package com.amap.login;

public interface ILoginView {

	void showProgress();

	void hideProgress();

	void userIdNotFoundError();

	void passwordNotFoundError();

	void userIdNullPointError();

	void passwordNullPointError();

	void onUserLoginError();

	void navigateToHome();

}

咱們分別定義了MVP模式中的表明M,V,P接口類。

package com.amap.login;

import android.content.Context;
import android.os.Handler;
import android.text.TextUtils;

import com.amap.bean.User;
import com.amap.common.UserDataManager;

public class LoginModelImpl implements ILoginModel{
	private UserDataManager mUserDataManager;
	public static final String PREFERENCE_NAME = "UserInfo";
	public static int MODE = Context.MODE_PRIVATE;
	public LoginModelImpl() {
		this.mUserDataManager = UserDataManager.getInstence();
	}

	@Override
	public void login(final String userid, final String password,final Context context, final OnLoginFinishedListener listener) {
		new Handler().postDelayed(new Runnable() {
			@Override
			public void run() {
				if (TextUtils.isEmpty(userid)) {
					listener.onUserIdNullPointError();
					return;
				}else if (TextUtils.isEmpty(password)) {
					listener.onPasswordNullPointError();
					return;
				}
				//User user = mUserDataManager.findUserByAccAndPwd(username,password);
				User user = mUserDataManager.fetchOneUser(userid);
				if(user == null){
					listener.onUserIdNotFoundError();
					return;
				} else{
					if (user.getPassword().equals(password)) {
						//if (user.getStatus().equals("1")) {
							
						//	listener.onUserLoginError();
						//	return;
						//} else {
							user.setUserId(userid);
							user.setPassword(password);
							user.setImage(user.getImage());
							user.setName(user.getName());
							mUserDataManager.saveSharedPreferences(user,
									context);
							user.setStatus("1");
							mUserDataManager.updateUserStatusByAcc(userid, "1");
							UserDataManager.setSelf(user);
							listener.onSuccess();
						//}
					} else {
						listener.onPasswordNotFoundError();
						return;
					}
					
				}
			}
		}, 1000);
	}


}

package com.amap.login;

import android.content.Context;


public class LoginPresenterImpl implements ILoginPresenter,OnLoginFinishedListener{

	ILoginModel loginModel = null;
	ILoginView loginView = null;
	
	public LoginPresenterImpl(ILoginView loginView) {
		
		loginModel = new LoginModelImpl();
		this.loginView = loginView;
	}
	
	@Override
	public void validateCredentials(String userid, String password, Context context) {
		if(loginView != null) {
			loginView.showProgress();
		}
		loginModel.login(userid, password, context, this);	
		
	}

	@Override
	public void onDestroy() {
		// TODO Auto-generated method stub		
	}

	@Override
	public void onSuccess() {
		if(loginView != null) {
			loginView.navigateToHome();
		}
	}

	@Override
	public void onUserIdNotFoundError() {
		// TODO Auto-generated method stub
		if(loginView != null) {
			loginView.userIdNotFoundError();
			loginView.hideProgress();
		}
	}

	@Override
	public void onUserIdNullPointError() {
		// TODO Auto-generated method stub
		if(loginView != null) {
			loginView.userIdNullPointError();
			loginView.hideProgress();
		}
	}

	@Override
	public void onPasswordNotFoundError() {
		// TODO Auto-generated method stub
		if(loginView != null) {
			loginView.passwordNotFoundError();
			loginView.hideProgress();
		}
	}

	@Override
	public void onPasswordNullPointError() {
		// TODO Auto-generated method stub
		if(loginView != null) {
			loginView.passwordNullPointError();
			loginView.hideProgress();
		}
	}
	
	@Override
	public void onUserLoginError() {
		// TODO Auto-generated method stub
		if(loginView != null) {
			loginView.onUserLoginError();
			loginView.hideProgress();
		}
	}
}

package com.amap.login;

public interface OnLoginFinishedListener {

	void onUserIdNotFoundError();

	void onUserIdNullPointError();

	void onPasswordNotFoundError();

	void onPasswordNullPointError();

	void onUserLoginError();

	void onSuccess();
}

package com.amap.activity;

import android.app.Activity;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import com.amap.customview.MyProgress;
import com.amap.friends.R;
import com.amap.login.ILoginView;
import com.amap.login.LoginPresenterImpl;

public class LoginActivity extends Activity implements OnClickListener,ILoginView {

	private EditText mAccount;
	private EditText mPwd;
	private Button button_login;
	private TextView user_register;
	private Dialog ProgressBar_login;
	private LoginPresenterImpl loginPresenterImpl;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		initView();
		initListener();
	}

	public void initView() {
		setContentView(R.layout.activity_login);
		mAccount = (EditText) findViewById(R.id.editText_useracc);
		mPwd = (EditText) findViewById(R.id.editText_password);
		button_login = (Button) findViewById(R.id.button_login);
		user_register = (TextView) findViewById(R.id.user_register);
		ProgressBar_login = MyProgress.createLoadingDialog(this, getString(R.string.login_msg));
		
	}

	public void initListener() {
		button_login.setOnClickListener(this);
		user_register.setOnClickListener(this);
		loginPresenterImpl = new LoginPresenterImpl(this);
	}

	public void login() {
		loginPresenterImpl.validateCredentials(mAccount.getText().toString()
				.trim(), mPwd.getText().toString().trim(), getApplicationContext());
	}

	@Override
	public void onClick(View v) {
		switch (v.getId()) {
		case R.id.button_login:
			login();
			break;
		case R.id.user_register:
			navigateToRegister();
			break;
		default:
			break;
		}
	}

	@Override
	public void showProgress() {
		// TODO Auto-generated method stub
		ProgressBar_login.show();
	}

	@Override
	public void hideProgress() {
		// TODO Auto-generated method stub
		ProgressBar_login.hide();
	}

	public void navigateToRegister() {
		// TODO Auto-generated method stub
		startActivity(new Intent(this, RegisterActivity.class));
		finish();
	}
	
	@Override
	public void navigateToHome() {
		// TODO Auto-generated method stub
		startActivity(new Intent(this, MainActivity.class));
		finish();
	}

	@Override
	public void userIdNotFoundError() {
		// TODO Auto-generated method stub
		Toast.makeText(this, R.string.login_userid_fail, Toast.LENGTH_SHORT).show();
	}

	@Override
	public void passwordNotFoundError() {
		// TODO Auto-generated method stub
		Toast.makeText(this, R.string.login_password_fail, Toast.LENGTH_SHORT).show();
	}

	@Override
	public void userIdNullPointError() {
		// TODO Auto-generated method stub
		Toast.makeText(this, R.string.account_empty, Toast.LENGTH_SHORT).show();
	}

	@Override
	public void passwordNullPointError() {
		// TODO Auto-generated method stub
		Toast.makeText(this, R.string.pwd_empty, Toast.LENGTH_SHORT).show();
	}

	@Override
	public void onUserLoginError() {
		// TODO Auto-generated method stub
		Toast.makeText(this, R.string.login_exist, Toast.LENGTH_SHORT).show();
	}
}

從以上的代碼能夠看出callback的好處。Activity中的代碼構造比較清晰易懂。

沒有calback基本不知道怎麼在別的class中操做之後更新UI。

有了callback能夠直接在別的class中簡潔的更新UI了。很是cool~~~

每日一句

每一个你不满意的现在，都有一个你没有努力的曾经。