带 AlertDialog 的 Singleton 使我的 Android 应用程序崩溃

Question

我是android新手，我正在尝试构建一个android应用程序，我使用单例模式来显示警报对话框，但是当我运行应用程序时它崩溃了。 我尝试删除单例，它工作正常。 这是我的代码 LoadingDialog.java

public class LoadingDialog {
    private Activity activity;
    private AlertDialog dialog;

    private static LoadingDialog loadDialog;

    public LoadingDialog(Activity activity) {
        this.activity = activity;
    }

    public static synchronized LoadingDialog getInstance(Activity activity) {
        if (loadDialog == null) {
            loadDialog = new LoadingDialog(activity);
        }
        return loadDialog;
    }

    public void startDialog() {
        AlertDialog.Builder builder = new AlertDialog.Builder(activity);
        LayoutInflater inflater = activity.getLayoutInflater();
        builder.setView(inflater.inflate(R.layout.loading,null));
        builder.setCancelable(false);
        dialog = builder.create();
        dialog.show();
    }

    public void closeDialog() {
        dialog. Dismiss();
    }
}

MainActivity.java

private ActivityMainBinding binding;
private LoadingDialog dialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());
        dialog = LoadingDialog.getInstance(MainActivity.this);
        binding.btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dialog.startDialog();
            }
        });

它给了我这个错误

FATAL EXCEPTION: main
Process: com.mkandeel.gmarek, PID: 20063
android.view.WindowManager$BadTokenException: Unable to add window -- token android.os.BinderProxy@4723521 is not valid; is your activity running?
at android.view.ViewRootImpl.setView(ViewRootImpl.java:678)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:342)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:93)
at android.app.Dialog.show(Dialog.java:316)
at com.mkandeel.gmarek.LoadingDialog.startDialog(LoadingDialog.java:30)
at com.mkandeel.gmarek.MainActivity$1.onClick(MainActivity.java:52)
at android.view.View.performClick(View.java:5610)
at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1211)
at android.view.View$PerformClick.run(View.java:22265)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)

那么我的代码有什么问题呢？ 预先感谢。

我尝试通过公开我的收缩器来使用没有单例的类，并且它可以正常工作

Answer 1

我认为错误是当你调用 startDialog() 时你的 Activity 为空：

binding = ActivityMainBinding.inflate(getLayoutInflater());
setContentView(binding.getRoot());
dialog = LoadingDialog.getInstance(MainActivity.this);
binding.btn.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
    dialog.startDialog();
    }
});

因为当您调用 getInstance 时，您通过 param 使用 Activity 创建了实例，但 LoadingDialog 范围内的 Activity 尚未初始化，因此为 null。然后，当你调用startDialog()时，Builder中的activity为null：

AlertDialog.Builder builder = new AlertDialog.Builder(activity);

因此，解决方案可能是：

 public static synchronized LoadingDialog getInstance(Activity activity) {
        if (loadDialog == null && this.activity == activity) {
            this.activity = activity;
            loadDialog = new LoadingDialog(activity);
        }
        return loadDialog;
    }

我也在检查活动实例，因为如果您从另一个活动调用单例类，则可能会导致内存泄漏。

无论如何，IMO 不需要单例类来显示对话框，也不需要

synchronized

关键字

Answer 2

当您显示不再存在的上下文/活动的对话框时，会发生此错误。

在调用 .show() 之前检查活动/上下文是否未完成

public void startDialog() {
    AlertDialog.Builder builder = new AlertDialog.Builder(activity);
    LayoutInflater inflater = activity.getLayoutInflater();
    builder.setView(inflater.inflate(R.layout.loading,null));
    builder.setCancelable(false);
    dialog = builder.create();
    
    if (!activity.isFinishing()){
         dialog.show();
    }
}