Android(安卓)不依赖于Activity的全局对话框Dialog

正常初始化对话框的写法

一般的Dialog对象初始化都需要依赖于Activity，如下

new AlertDialog.Builder(activity)        .setTitle("野猿新一")        .setMessage("我是对话框内容啦")        .show();

BroadcastReceiver如果是在Activity中注册的，用onReceive(Context context, Intent intent)方法的context参数来初始化Dialog是可以正常弹出对话框的。因为这里的context其实是一个Activity对象，如下所示：

public class MainActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        registerReceiver(new BroadcastReceiver() {            @Override            public void onReceive(Context context, Intent intent) {                if (context instanceof Activity) {                    new AlertDialog.Builder(context)                            .setTitle("野猿新一")                            .setMessage("我是对话框内容啦")                            .show();                }            }        }, new IntentFilter("com.him.action"));    }}

会报错的写法

虽说AlertDialog.Builder(Context context)的参数是Context，但是如果传入的是非Activity的Context，比如说Application，就会报如下所示的错误

android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application        at android.view.ViewRootImpl.setView(ViewRootImpl.java:700)        at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:289)        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)        at android.app.Dialog.show(Dialog.java:298)        at android.app.AlertDialog.show(AlertDialog.java:1128)        at android.app.AlertDialog$Builder.show(AlertDialog.java:1008)        at com.him.autosizingtest.MainActivity$1.onClick(MainActivity.java:21)        at android.view.View.performClick(View.java:4918)        at android.view.View$PerformClick.run(View.java:20399)        at android.os.Handler.handleCallback(Handler.java:815)        at android.os.Handler.dispatchMessage(Handler.java:104)        at android.os.Looper.loop(Looper.java:194)        at android.app.ActivityThread.main(ActivityThread.java:5869)        at java.lang.reflect.Method.invoke(Native Method)        at java.lang.reflect.Method.invoke(Method.java:372)        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1019)        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:814)

所以以下的几种写法都会报错

new AlertDialog.Builder(activity.getApplication())        .setTitle("野猿新一")        .setMessage("我是对话框内容啦")        .show();new AlertDialog.Builder(activity.getApplicationContext())        .setTitle("野猿新一")        .setMessage("我是对话框内容啦")        .show();

BroadcastReceiver如果是在Manifest中声明的，用onReceive(Context context, Intent intent)方法的context参数来初始化Dialog，一样还会报Unable to add window -- token null is not for an application错误。所以如下写法也不可行

public class MyBroadcastReceiver extends BroadcastReceiver {    @Override    public void onReceive(Context context, Intent intent) {        new AlertDialog.Builder(context)                .setTitle("野猿新一")                .setMessage("我是对话框内容啦")                .show();    }}// 在manifest中声明

全局Dialog

但是如果说有些情况下获取不到Activity对象，但是又想弹出Dialog呢？这时候用全局的Dialog是可以实现的。

只需要设置dialog为WindowManager.LayoutParams.TYPE_SYSTEM_ALERT类型

然后添加android.permission.SYSTEM_ALERT_WINDOW权限

Dialog dialog = new AlertDialog.Builder(activity.getApplicationContext())        .setTitle("野猿新一")        .setMessage("我是对话框内容啦")        .create();// 增加这句代码dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);dialog.show();// 然后在manifest中添加权限

正常初始化对话框的写法

会报错的写法

全局Dialog

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