android之Activity的创建与关闭

Activity的启动和关闭

1.启动activity

activity的启动分为两种，一种为入口activity，另一种为其他activity

在AndroidManifests进行配置，入口activity的启动只要在要启动的activity里加入intent，例如下面代码将MainActivity作为入口Activity

<activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
</activity>

那其他activity如何启动呢?

答案是：startActivity来进行启动，通过intent对象获得要启动的activity，再进行启动。

 psw.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(MainActivity.this,ForgetpswActivity.class);
                startActivity(intent);
            }
        });

2.关闭Activity

直接调用finish（）即可关闭当前的活动，需要注意的是，当需要关闭的活动不是主活动而是其他活动时，关闭后就会回到主活动；如果要关闭的活动是主活动

则就直接返回手机主屏幕。

close.setOnClickListener(new View.OnClickListener() {  //为关闭按钮创建监听事件
            @Override
            public void onClick(View v) {
                
                finish(); //关闭当前Activity
            }
        });

小妙招：刷新当前Activity------》onCreat(null);

Activity启动与关闭的实例：

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/biaoge"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/zhanghao"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="账号："
        android:textSize="25sp"
        app:layout_constraintBottom_toTopOf="@+id/idpsw"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.145"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.924"
        tools:ignore="MissingConstraints" />

    <EditText
        android:id="@+id/edtzhanghao"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="邮箱或者手机号"

        app:layout_constraintStart_toEndOf="@+id/idpsw"
        app:layout_constraintTop_toTopOf="@+id/zhanghao"
        tools:ignore="MissingConstraints" />

    <TextView
        android:id="@+id/idpsw"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="1dp"
        android:layout_marginLeft="1dp"

        android:text="密码："
        android:textSize="25sp"
        app:layout_constraintBaseline_toBaselineOf="@+id/edtpsw"
        app:layout_constraintStart_toStartOf="@+id/btnzhuce"
        tools:ignore="MissingConstraints" />

    <EditText
        android:id="@+id/edtpsw"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="1dp"

        android:layout_marginLeft="1dp"
        android:layout_marginBottom="205dp"
        android:hint="输入6-16位数字或密码"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@+id/idpsw"
        tools:ignore="MissingConstraints" />

    <Button
        android:id="@+id/btnzhuce"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="48dp"
        android:layout_marginLeft="48dp"
        android:text="注册"
        app:layout_constraintBaseline_toBaselineOf="@+id/btnlogin"
        app:layout_constraintStart_toStartOf="parent"
        tools:ignore="MissingConstraints" />

    <Button
        android:id="@+id/btnlogin"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:background="#FF8247"
        android:text="登录"
        app:layout_constraintEnd_toStartOf="@+id/wang_psw"
        app:layout_constraintTop_toBottomOf="@+id/edtpsw"
        tools:ignore="MissingConstraints" />

    <TextView
        android:id="@+id/wang_psw"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="19dp"
        android:layout_marginEnd="76dp"
        android:layout_marginRight="76dp"
        android:background="#FF8247"
        android:text="忘记密码？"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnlogin"
        tools:ignore="MissingConstraints" />

</androidx.constraintlayout.widget.ConstraintLayout>

activity_forgetpsw.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/beijing"
    tools:context=".ForgetpswActivity">

    <ImageButton
        android:id="@+id/close"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="3dp"
        android:layout_marginLeft="3dp"
        android:layout_marginTop="16dp"
        android:background="#0000"
        android:src="@drawable/guanbi"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="MissingConstraints" />


    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="33dp"

        android:layout_marginLeft="33dp"
        android:layout_marginTop="124dp"
        android:text="你的邮箱或手机号"
        android:textSize="15sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="MissingConstraints" />

    <EditText
        android:id="@+id/edtemailorphone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="33dp"
        android:layout_marginLeft="33dp"
        android:layout_marginTop="28dp"
        android:hint="请输入手机号或邮箱"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <Button
        android:id="@+id/btnok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="56dp"
        android:layout_marginLeft="56dp"
        android:layout_marginTop="48dp"
        android:layout_marginEnd="58dp"
        android:layout_marginRight="58dp"
        android:background="#fff000"
        android:text="确定"
        app:layout_constraintEnd_toEndOf="@+id/edtemailorphone"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/edtemailorphone" />


</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.example.forgetpsw;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView psw=(TextView)findViewById(R.id.wang_psw);
        psw.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(MainActivity.this,ForgetpswActivity.class);
                startActivity(intent);
            }
        });
    }
}

ForgetpswActivity.java

package com.example.forgetpsw;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageButton;

public class ForgetpswActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_forgetpsw);
        ImageButton close = (ImageButton) findViewById(R.id.close); //获取布局文件中的关闭按钮
        close.setOnClickListener(new View.OnClickListener() {  //为关闭按钮创建监听事件
            @Override
            public void onClick(View v) {

                finish(); //关闭当前Activity
            }
        });
    }
}

项目截图：当点击忘记密码会启动忘记密码事件，当点击叉号就会回到主活动。