Activity技术

注：以下内容来自第四章

一、定时更新Activity背景图

需要用到定时器用法：Timer + TimerTask

布局

<?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:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/bg1080"
    tools:context=".MyActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="66dp"
        android:layout_marginEnd="16dp"
        android:layout_marginBottom="100dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0"
        app:srcCompat="@drawable/gu" />
</androidx.constraintlayout.widget.ConstraintLayout>

代码

package com.dzh.review;

import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;

import android.os.Bundle;

import java.util.Timer;
import java.util.TimerTask;

public class MyActivity extends AppCompatActivity {
    private int idx = 0; //图片序号
    private ConstraintLayout layout; //布局

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);

        layout = (ConstraintLayout) findViewById(R.id.constraintLayout);
        int[]resIds = new int[]{R.drawable.bg1080,R.drawable.bg1080_2};
        Timer timer = new Timer();
        TimerTask task = new TimerTask() {
            @Override
            public void run() {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        layout.setBackgroundResource(resIds[idx]);
                        if(idx < resIds.length - 1)idx++;
                        else idx = 0;
                    }
                });
            }
        };
        timer.schedule(task,3000,5000);
    }
}

说明：

Android规定只有主线程才能更新UI，在TimerTask线程中是不能直接更新UI的，但可调用runOnUIThread方法将一个Runnable子线程任务放到主线程中执行

 

二、创建Acticity选项菜单

步骤：

1. 创建菜单资源
2. 重写onCreatOptionsMenu方法——创建选项菜单
3. 重写onOptionsItemSelected方法——为菜单项添加选中事件

完整代码：

package com.dzh.review;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;

import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

import java.util.Timer;
import java.util.TimerTask;

public class MyActivity extends AppCompatActivity {
    private int idx = 0; //图片序号
    private ConstraintLayout layout; //布局

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);

        layout = (ConstraintLayout) findViewById(R.id.constraintLayout);
        int[]resIds = new int[]{R.drawable.bg1080,R.drawable.bg1080_2};
        Timer timer = new Timer();
        TimerTask task = new TimerTask() {
            @Override
            public void run() {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        layout.setBackgroundResource(resIds[idx]);
                        if(idx < resIds.length - 1)idx++;
                        else idx = 0;
                    }
                });
            }
        };
        timer.schedule(task,3000,5000);
    }

    public boolean onCreatOptionsMenu(Menu menu){
        getMenuInflater().inflate(R.menu.main_menu,menu);
        return super.onCreateOptionsMenu(menu);
    }

    public boolean onOptionsItemSelected(@NonNull MenuItem item){
        switch (item.getItemId()){
            case R.id.menu_login:
                Toast.makeText(MyActivity.this,"登录成功",Toast.LENGTH_LONG).show();
                break;
            case R.id.menu_exit:
                finish();
                break;
        }
        return super.onOptionsItemSelected(item);
    }
}