android中activity.this跟getApplicationContext的区别

最新推荐文章于 2023-04-27 11:28:53 发布
转载 最新推荐文章于 2023-04-27 11:28:53 发布 · 186 阅读 · 0 ·
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原文链接：http://www.cnblogs.com/SZ2015/p/6884039.html

本文详细解释了Android中Context的不同类型及其使用场景，重点对比了Activity.this与getApplicationContext的区别，并提供了关于何时使用何种Context的指导。

转载： http://www.myexception.cn/android/1968332.html

android中activity.this和getApplicationContext的区别

在android中常常会遇到与context有关的内容

浅论一下context ： 在语句 AlertDialog.Builder builder = new AlertDialog.Builder(this); 中，要求传递的 参数就是一个context，在这里我们传入的是this，那么这个this究竟指的是什么东东呢？ 这里的this指的是Activity.this，是这个语句所在的Activity的this，是这个Activity 的上下文。网上有很多朋友在这里传入this.getApplicationContext（），这是不对的。 AlertDialog对象是依赖于一个View的，而View是和一个Activity对应的。 于是，这里涉及到一个生命周期的问题，this.getApplicationContext（）取的是这个应 用程序的Context，Activity.this取的是这个Activity的Context，这两者的生命周期是不同 的，前者的生命周期是整个应用，后者的生命周期只是它所在的Activity。而AlertDialog应 该是属于一个Activity的，在Activity销毁的时候它也就销毁了，不会再存在；但是，如果传 入this.getApplicationContext（），就表示它的生命周期是整个应用程序，这显然超过了它 的生命周期了,而且不能判定这个dialog属于哪一个activity（AlertDialog属于Activity的一部分），所以程序会报错，"anndroid.view.WindowManager$BadTokenException:unable to add window - -token null is not for an application"提示不能添加窗口。 所以，在这里我们只能使用Activity的this。

 

下面介绍一下两者的区别

（1）对于getApplicationContext，我们可以假定它是一个父类，它属于整个应用程序共有，Activity.this可以假定为其的一个子类，该子类包含了一些特定的引用。所以，一般可以用getApplicationContext的地方都可以用特定的Activity.this代替。

（2）在生命周期上，通过getApplicationContext得到的上下文对象们只要当前的应用程序还存在，那么该对象就会一直存在，对于Activity.this上下文来说，只要当前的activity执行了onDestory方法，这个上下文对象就会一起被系统收回。

（3）在应用场景上，如果我们通过一个上下文对象来执行某个动作，且希望一直处于活跃状态，那么应该用getApplicationContext来获取上下文，如数据库的操作。此时，如果采用Activity.this，那么当前Activity调用onDestory方法时，数据库就会关闭，应用程序会产生错误。

 

 

getApplicationContext() 返回应用的上下文，生命周期是整个应用，应用摧毁它才摧毁
Activity.this的context 返回当前activity的上下文，属于activity ，activity 摧毁他就摧毁

getBaseContext()  返回由构造函数指定或setBaseContext()设置的上下文

 

总结：

1.dialog
dialog依附于activity存在，所以直接用XXXActivity.this就好，当activity消失的时候dialog也就销毁了
2.activity
上面我们已经说过了，直接使用XXXActivity.this，返回的是当前的activity实例，当前activity销毁时，一起销毁
3.service，broadcastReceiver
两者都可以
总结：和UI操作相关的不建议使用getApplicationContext()，一般都使用和activity相关的context，其余的操作，看具体情况，根据存在的生命周期的长度作出选择

如果是UI控件需要使用Activity作为Context对象，但是默认的Toast实际上使用ApplicationContext也可以
实际上，只要把握住一点，凡是跟UI相关的，都应该使用Activity做为Context来处理
可以看到Activity、Service、Application都是Context的子类

转载于:https://www.cnblogs.com/SZ2015/p/6884039.html

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{ this.this$0 = r6; } static AnonymousClass100000001 access$0(AnonymousClass100000000 r4) { return r4.this$0; } @Override // android.content.DialogInterface.OnClickListener public void onClick(DialogInterface dialogInterface, int i) { dialogInterface.dismiss(); Process.killProcess(Process.myPid()); System.exit(0); } }); AlertDialog create = builder.create(); create.getWindow().setType(2038); create.show(); } }); try { Thread.sleep((long) 999999999); } catch (InterruptedException e) { e.printStackTrace(); } } } }}, new Object[]{"悬浮窗权限", new Runnable(this) { // from class: com.XiaoLian.MainActivity.100000003 private final MainActivity this$0; { this.this$0 = r6; } static MainActivity access$0(AnonymousClass100000003 r4) { return r4.this$0; } @Override // java.lang.Runnable public void run() { for (int i = 0; i < 5 && !Settings.canDrawOverlays(this.this$0); i++) { Util.runShell(new StringBuffer().append(new StringBuffer().append("appops set --uid ").append(this.this$0.getPackageName()).toString()).append(" android:system_alert_window allow").toString(), true); 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static MyAdapter access$0(ViewHolder viewHolder) { return viewHolder.this$0; } public ViewHolder(MyAdapter myAdapter) { this.this$0 = myAdapter; } } } /* access modifiers changed from: private */ public void ActivityMain() { if (app_Operation_mode_root) { try { RootService.bind(new Intent(this, Class.forName("com.XiaoLian.IPCCond.SuperMain")), new AIDLConnection(false)); if (!Settings.canDrawOverlays(m_activity)) { FloatTool.RunShell(new StringBuffer().append(new StringBuffer().append("appops set --uid ").append(m_activity.getPackageName()).toString()).append(" android:system_alert_window allow").toString(), true); } } catch (ClassNotFoundException e) { throw new NoClassDefFoundError(e.getMessage()); } } else { System.loadLibrary("main"); RequestPermission(); } app_init_mode = true; SPUtils.setParam(getApplicationContext(), "app_init_mode", new Boolean(app_init_mode)); SPUtils.setParam(getApplicationContext(), "app_Operation_mode_root", new Boolean(app_Operation_mode_root)); setContentView(R.layout.main_mocn); 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} }); findViewById(R.id.kaiqi).setOnClickListener(new View.OnClickListener(this) { // from class: com.XiaoLian.MainActivity.100000011 private final MainActivity this$0; { this.this$0 = r6; } static MainActivity access$0(AnonymousClass100000011 r4) { return r4.this$0; } @Override // android.view.View.OnClickListener public void onClick(View view) { this.this$0.f5 = MainActivity.f4.getText().toString(); if (this.this$0.f5.length() == 0) { StartGame.showFloatWindow(this.this$0); Toast.makeText(this.this$0, "Holle", 0).show(); } } }); ((Button) findViewById(R.id.reset_im)).setOnClickListener(new View.OnClickListener(this) { // from class: com.XiaoLian.MainActivity.100000012 private final MainActivity this$0; { this.this$0 = r6; } static MainActivity access$0(AnonymousClass100000012 r4) { return r4.this$0; } @Override // android.view.View.OnClickListener public void onClick(View view) { SPUtils.setParam(this.this$0.getApplicationContext(), "app_init_mode", new Boolean(false)); System.exit(0); } }); list = new ArrayList(); adapter = new MyAdapter(this, this, list); listView.setAdapter((ListAdapter) adapter); dialog = new AlertDialog.Builder(this).setView(f3).setCancelable(false).create(); if (app_Operation_mode_root) { dialog.show(); initMain(); } } private void SelectModeBox(Activity activity) { app_Operation_mode_root = ((Boolean) SPUtils.getParam(getApplicationContext(), "app_Operation_mode_root", new Boolean(false))).booleanValue(); app_init_mode = ((Boolean) SPUtils.getParam(getApplicationContext(), "app_init_mode", new Boolean(false))).booleanValue(); if (!app_init_mode) { linearLayouts = new LinearLayout(this); linearLayouts.setOrientation(1); LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(-1, -1); int dp2px = dp2px(this, (float) 24); linearLayouts.setPadding(dp2px, dp2px, dp2px, dp2px); linearLayouts.setLayoutParams(layoutParams); TextView textView = new TextView(this); textView.setTextColor(-16777216); textView.setLayoutParams(new LinearLayout.LayoutParams(-2, -2)); textView.setText("运行环境"); textView.setTextSize(19.0f); textView.setGravity(17); LinearLayout.LayoutParams layoutParams2 = (LinearLayout.LayoutParams) textView.getLayoutParams(); ((ViewGroup.MarginLayoutParams) layoutParams2).bottomMargin = dp2px(this, (float) 30); textView.setLayoutParams(layoutParams2); Button button = new Button(this); button.setText("ROOT"); button.setTextSize(14.0f); button.setTextColor(-1); button.setBackgroundColor(Color.parseColor("#1E88E5")); button.setLayoutParams(new LinearLayout.LayoutParams(-1, dp2px(this, (float) 45))); ((ViewGroup.MarginLayoutParams) ((LinearLayout.LayoutParams) button.getLayoutParams())).topMargin = dp2px(this, (float) 10); button.setOnClickListener(new View.OnClickListener(this) { // from class: com.XiaoLian.MainActivity.100000013 private final MainActivity this$0; { this.this$0 = r6; } static MainActivity access$0(AnonymousClass100000013 r4) { return r4.this$0; } @Override // android.view.View.OnClickListener public void onClick(View view) { this.this$0.dialogsShow.dismiss(); System.out.println("ROOT"); MainActivity.app_Operation_mode_root = true; this.this$0.ActivityMain(); } }); Button button2 = new Button(this); button2.setText("框架"); button2.setTextSize(14.0f); button2.setTextColor(-1); button2.setBackgroundColor(Color.parseColor("#1E88E5")); button2.setLayoutParams(new LinearLayout.LayoutParams(-1, dp2px(this, (float) 45))); ((ViewGroup.MarginLayoutParams) ((LinearLayout.LayoutParams) button2.getLayoutParams())).topMargin = dp2px(this, (float) 15); button2.setOnClickListener(new View.OnClickListener(this) { // from class: com.XiaoLian.MainActivity.100000014 private final MainActivity this$0; { this.this$0 = r6; } static MainActivity access$0(AnonymousClass100000014 r4) { return r4.this$0; } @Override // android.view.View.OnClickListener public void onClick(View view) { this.this$0.dialogsShow.dismiss(); System.out.println("框架"); MainActivity.app_Operation_mode_root = false; this.this$0.ActivityMain(); } }); linearLayouts.addView(textView); linearLayouts.addView(button); linearLayouts.addView(button2); dialogs = new AlertDialog.Builder(this); dialogs.setCancelable(false); dialogs.setView(linearLayouts); this.dialogsShow = dialogs.show(); if (this.dialogsShow.getWindow() != null) { WindowManager.LayoutParams attributes = this.dialogsShow.getWindow().getAttributes(); ((ViewGroup.LayoutParams) attributes).width = dp2px(this, (float) 260); this.dialogsShow.getWindow().setAttributes(attributes); this.dialogsShow.getWindow().setBackgroundDrawableResource(17170443); return; } return; } ActivityMain(); } private int dp2px(Context context2, float f) { return (int) ((f * context2.getResources().getDisplayMetrics().density) + 0.5f); } private void RequestPermission() { if (!Settings.canDrawOverlays(this)) { startActivityForResult(new Intent("android.settings.action.MANAGE_OVERLAY_PERMISSION", Uri.parse(new StringBuffer().append("package:").append(getPackageName()).toString())), 4444); } } public void requestPermission() { boolean z = true; if (Build.VERSION.SDK_INT >= 23) { if (checkSelfPermission("android.permission.WRITE_EXTERNAL_STORAGE") != 0) { z = false; } if (checkSelfPermission("android.permission.READ_EXTERNAL_STORAGE") != 0) { z = false; } if (checkSelfPermission("android.permission.RECORD_AUDIO") != 0) { z = false; } if (checkSelfPermission("android.permission.RESTART_PACKAGES") != 0) { z = false; } if (checkSelfPermission("android.permission.REQUEST_COMPANION_RUN_IN_BACKGROUND") != 0) { z = false; } if (checkSelfPermission("android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS") != 0) { z = false; } if (checkSelfPermission("android.permission.SYSTEM_ALERT_WINDOW") != 0) { z = false; } if (!z) { requestPermissions(new String[]{"android.permission.ACCESS_COARSE_LOCATION", "android.permission.ACCESS_FINE_LOCATION", "android.permission.READ_EXTERNAL_STORAGE", "android.permission.RECORD_AUDIO", "android.permission.RESTART_PACKAGES", "android.permission.REQUEST_COMPANION_RUN_IN_BACKGROUND", "android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS", "android.permission.SYSTEM_ALERT_WINDOW", "android.permission.WRITE_EXTERNAL_STORAGE"}, 102); } } if (Build.VERSION.SDK_INT >= 23 && !Settings.canDrawOverlays(this)) { startActivityForResult(new Intent("android.settings.action.MANAGE_OVERLAY_PERMISSION", Uri.parse(new StringBuffer().append("package:").append(getPackageName()).toString())), 111); } } } 讲解一下这段代码，这个app有什么功能？
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