Android应用组件Activity

一、Activity简介

1、Activity拥有可以编辑用户界面的窗口，窗口布满整个屏幕，也可以小于或者漂浮于其他窗口之上

2、应用程序通常拥有多个互相关联的Activity和一个MainActivity

多个Activity之间跳转简单示意

二、Acitivity生命周期

Activity的声明周期是指Activity所经历的所有状态

Activty的完整生命周期是指 从第一次调用onCreate（）方法开始，直到调用onDrestroy（）方法位置。

Activity的可视生命周期是指 自onStart()调用开始直到相应的onStop()调用结束。在此期间，用户可以在屏幕上看到Activity。

Activity的前台生命周期是指 onResume()调用起，至相应的onPause()调用为止。在此期间，Activity位于前台最上面并与用户进行交互。

三、Activity的状态保存

通过onSaveInstance（）方法，回收当前Activty时回调该方法

例：

package com.songjialongs.myapplication;import android.os.PersistableBundle;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.widget.CheckBox;import android.widget.CompoundButton;import android.widget.EditText;public class Activity_Lifecycle extends AppCompatActivity {    EditText user_name_et;    CheckBox rem_user_name_cb;    boolean iscckeck = false;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__lifecycle);        user_name_et = (EditText) findViewById(R.id.user_name_et);        rem_user_name_cb = (CheckBox) findViewById(R.id.rem_user_name_cb);        iscckeck = savedInstanceState.getBoolean("remname");        rem_user_name_cb.setChecked(iscckeck);        final String name = savedInstanceState.getString("name");        rem_user_name_cb.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {            @Override            public void onCheckedChanged(CompoundButton compoundButton, boolean b) {                if (b) {                    user_name_et.setText(name);                    iscckeck = true;                } else {                    iscckeck = false;                }            }        });    }    @Override    public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {        super.onSaveInstanceState(outState, outPersistentState);        String content = user_name_et.getText().toString();        outState.putString("name", content);//参数为String Key，String Value        outState.putBoolean("remname", iscckeck);//参数为String Key，boolean Value    }}

layout代码：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent">    <TextView        android:id="@+id/user_name_txt"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_marginLeft="20dp"        android:layout_marginTop="20dp"        android:text="用户名:"        android:textSize="32sp" />    <EditText        android:id="@+id/user_name_et"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_marginRight="20dp"        android:layout_marginTop="20dp"        android:layout_toRightOf="@id/user_name_txt" />    <CheckBox        android:id="@+id/rem_user_name_cb"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignRight="@id/user_name_et"        android:layout_below="@id/user_name_et"        android:text="记住密码"        android:textSize="24sp" /></RelativeLayout>

四、Activity启动模式LaunchMode

LaunchMode是在Activity跳转的过程中，决定是否生成新的Activity，是否重用已经存在的，是否和其他实例公用一个task stack

1、Standard模式

Standard模式是默认启动模式，每次跳转Activity即StartActivty时都会生成一个新的Activity并压入系统默认的task stack中

package com.songjialongs.myapplication.LuancherMode;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class MainActivity extends AppCompatActivity {    TextView activty_A_Txt;    Button activty_A_Btn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__main);        activty_A_Txt = (TextView) findViewById(R.id.activty_a_txt);        activty_A_Btn = (Button) findViewById(R.id.activity_a_btn);        activty_A_Txt.setText(this.toString());        activty_A_Btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(MainActivity.this, Activity_Stardard_B.class);                startActivity(intent);            }        });    }}

import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class Activity_Stardard_B extends AppCompatActivity {    TextView activty_B_Txt;    Button activty_B_Btn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__stardard);        activty_B_Txt = (TextView) findViewById(R.id.stardard_b_txt);        activty_B_Btn = (Button) findViewById(R.id.stardard_b_btn);        activty_B_Txt.setText(this.toString());        activty_B_Btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(Activity_Stardard_B.this, MainActivity.class);                startActivity(intent);            }        });    }}

2、SingleTop模式

要跳转的Activity已经存在与系统的task中，并且位于栈顶，就使用栈顶的相同的Activity；若不存在，则创建一个新的Activty，并压入系统默认的task stack

package com.songjialongs.myapplication.LuancherMode;import android.app.Activity;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class MainActivity extends AppCompatActivity {    TextView activty_A_Txt;    Button activty_A_Btn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__main);        activty_A_Txt = (TextView) findViewById(R.id.activty_a_txt);        activty_A_Btn = (Button) findViewById(R.id.activity_a_btn);        activty_A_Txt.setText(this.toString());        activty_A_Btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(MainActivity.this, Activity_SingleTop_B.class);                startActivity(intent);            }        });    }}

package com.songjialongs.myapplication.LuancherMode;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class Activity_SingleTop_B extends AppCompatActivity {    TextView singletop_B_Btn_Txt;    Button singletop_B_Btn_btn;    Button singletop_BtoA_Btn_Txt;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__singletop__b);        singletop_B_Btn_Txt = (TextView) findViewById(R.id.singletop_b_btn_txt);        singletop_B_Btn_btn = (Button) findViewById(R.id.singletop_b_btn);        singletop_BtoA_Btn_Txt = (Button) findViewById(R.id.singletop_btoa_btn);        singletop_B_Btn_Txt.setText(this.toString());        singletop_B_Btn_btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(Activity_SingleTop_B.this, Activity_SingleTop_B.class);                startActivity(intent);            }        });        singletop_BtoA_Btn_Txt.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(Activity_SingleTop_B.this, MainActivity.class);                startActivity(intent);            }        });    }}

3、SingleTask模式

要跳转的Activity已经存在与栈中，就直接跳转至这个Activity；若不存在就创建一个新的Activity，并压入系统默认的task stack

package com.songjialongs.myapplication.LuancherMode;import android.app.Activity;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class MainActivity extends AppCompatActivity {    TextView activty_A_Txt;    Button activty_A_Btn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__main);        activty_A_Txt = (TextView) findViewById(R.id.activty_a_txt);        activty_A_Btn = (Button) findViewById(R.id.activity_a_btn);        activty_A_Txt.setText(this.toString());        activty_A_Btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(MainActivity.this, Activity_SingleTask_B.class);                startActivity(intent);            }        });    }}

package com.songjialongs.myapplication.LuancherMode;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class Activity_SingleTask_B extends AppCompatActivity {    TextView activty_B_Txt;    Button activty_B_Btn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__singletask);        activty_B_Txt = (TextView) findViewById(R.id.singletask_b_txt);        activty_B_Btn = (Button) findViewById(R.id.singletask_b_btn);        activty_B_Txt.setText(this.toString());        activty_B_Btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(Activity_SingleTask_B.this, MainActivity.class);                startActivity(intent);            }        });    }}

4、SingleInstance模式

跳转Acitivity 新建一个task stack，将跳转的Activity压入这个task stack，并且新建的task stack只有一个Activity

import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class MainActivity extends AppCompatActivity {    TextView activty_A_Txt;    Button activty_A_Btn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        activty_A_Txt = (TextView) findViewById(R.id.activty_a_txt);        activty_A_Btn = (Button) findViewById(R.id.activity_a_btn);        activty_A_Txt.setText(this.toString() + "：栈：" + getTaskId());        activty_A_Btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(MainActivity.this, Activity_SingleInstance_B.class);                startActivity(intent);            }        });    }}

package com.songjialongs.myapplication.LuancherMode;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.songjialongs.myapplication.R;public class Activity_SingleInstance_B extends AppCompatActivity {    TextView singinstance_B_Txt;    Button singinstance_B_Btn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity__singleinstance);        singinstance_B_Txt = (TextView) findViewById(R.id.singleinstance_b_txt);        singinstance_B_Btn = (Button) findViewById(R.id.singleinstance_b_btn);        singinstance_B_Txt.setText(this.toString() + "：栈：" + getTaskId());        singinstance_B_Btn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent(Activity_SingleInstance_B.this, Activity_SingleInstance_B.class);                startActivity(intent);            }        });    }}