Activity是Android最常用最基本的四大組件之一,Activity是一個應用程序組件,提供一個屏幕,用戶可以用來交互完成某項操作。
Activity中的所有操作都跟用戶有關係,是一個跟用戶交互的組件,可以通過SetContentView(View)來顯示指定控件。
- Activity生命週期
Acivity一共有七個生命週期:
一般簡單的生命週期:onCreate()->onStart()->onResume()->onPause()->onStop()->onDestory()
啓動Activity:onCreate()->onStart()->onResume()
當前Activity被覆蓋:onPause()
當Activity由覆蓋回到前臺:onResume()
當Activity轉到新的Activity界面:onPause()->onStop()
->onDestory()
用戶後退到此Activity:onRestart()->onStart()->onResume()
package com.appress.gerber.myapplication;
import android.content.Context;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
private static final String TAG = "LifeCycleActivity";
private Context mContext = this;
private int param = 1;
//Activity創建時被調用
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.i(TAG,"onCreated");
setContentView(R.layout.activity_main);
Button btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(mContext,TargetActivity.class);
startActivity(intent);
}
});
}
//Activity創建或從後臺重新回到前臺被調用
@Override
protected void onStart() {
super.onStart();
Log.i(TAG,"onStart");
}
//Activity從後臺重新回到前臺時被調用
@Override
protected void onRestart() {
super.onRestart();
Log.i(TAG,"onRestart");
}
//Activity創建或者從覆蓋、後臺回到前臺被調用
@Override
protected void onResume() {
super.onResume();
Log.i(TAG,"onResume");
}
//被覆蓋到下面或者被鎖屏
@Override
protected void onPause() {
super.onPause();
Log.i(TAG,"onPause");
}
//退出當前Activity或者跳轉到新的Activity
@Override
protected void onStop() {
super.onStop();
Log.i(TAG,"onStop");
}
//退出當前Activity,調用之後Activity就結束了
@Override
protected void onDestroy() {
super.onDestroy();
Log.i(TAG,"onDestory");
}
/**
* Activity被系統殺死之後調用
* 屏幕方向改變時,Activity被銷燬在重建;
* 在onPause之前使用
*/
@Override
protected void onSaveInstanceState(Bundle outState) {
outState.putInt("param",param);
Log.i(TAG,"onSaveInstanceState:"+ param);
super.onSaveInstanceState(outState);
}
/**
*Activity被系統殺死後又被重新創建
*屏幕方向改變時,Activity被銷燬再重建;
* 在onStart之後
*/
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
param = savedInstanceState.getInt("param");
Log.i(TAG,"onRestoreInstanceState" + param);
super.onRestoreInstanceState(savedInstanceState);
}
}
結果:
1. 啓動Activity:
2. 跳轉到其他頁面(Home鍵退回):
3. 從其他頁面返回(從後臺到前臺):
4. 銷燬Activity
5. 橫豎屏切換
在做橫豎屏切換時,onSaveInstanceState保存了臨時數據,切換完畢後onRestoreInstanceState取出剛剛保存的數據。