Question

我在自己的Java类中有一个AlertDialog。其中一个选项是启动一个Activity，但此时似乎不可能，因为我总是以java.lang.NullPointerException结束。

这是AlertDialog的代码，YallDoneDialog.java：

import android.app.Dialog;
import android.content.Context;
import android.support.v4.app.DialogFragment;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;

public class YallDoneDialog extends DialogFragment {

    private Context mContext;

    public YallDoneDialog() {

    }


    public static YallDoneDialog newInstance(String title) {
        YallDoneDialog frag = new YallDoneDialog();
        Bundle args = new Bundle();
        args.putString("title", title);
        frag.setArguments(args);
        return frag;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setMessage(R.string.done)
                .setTitle(R.string.done_title)
                .setPositiveButton(R.string.y, new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        MenuActivity m = new MenuActivity();
                        String resName = m.getResName();

                        LaunchBill l = new LaunchBill(mContext, getActivity());
                        l.LaunchTheDuckingBill(resName);
                    }
                })
                .setNegativeButton(R.string.n, new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        dismiss();
                    }
                });
        return builder.create();
    }


}

您将看到来自LaunchBill.java的名为LaunchTheDuckingBill的方法被称为肯定按钮的操作。这是代码：

import android.app.Activity;
import android.content.Context;
import android.content.Intent;

public class LaunchBill {

    private Context mContext;
    private Activity mActivity;

    public LaunchBill(Context mContext, Activity mActivity){
        this.mContext = mContext;
        this.mActivity = mActivity;
    }

    public void LaunchTheDuckingBill(String resName){
        Intent intent = new Intent(mContext, BillActivity.class);
        intent.putExtra("resName",resName);
        mContext.startActivity(intent);
    }

}

这是崩溃的整个堆栈跟踪：

05-13 20:45:10.836 21191-21191/com.whatamidoingwithmylife.splitbill E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.whatamidoingwithmylife.splitbill, PID: 21191
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
        at android.content.ComponentName.<init>(ComponentName.java:128)
        at android.content.Intent.<init>(Intent.java:4916)
        at com.whatamidoingwithmylife.splitbill.LaunchBill.LaunchTheDuckingBill(LaunchBill.java:18)
        at com.whatamidoingwithmylife.splitbill.YallDoneDialog$2.onClick(YallDoneDialog.java:74)
        at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:162)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6186)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)

你能告诉我出错的地方吗？我尝试过多种解决方案，但都会产生同样的错误。

Answer 1

第1步：从private Context mContext;删除YallDoneDialog。

第2步：将LaunchBill l = new LaunchBill(mContext, getActivity());替换为LaunchBill l = new LaunchBill(getActivity(), getActivity());

尝试从独立的AlertDialog启动活动

1 个答案: