Question

我在MainActivity中创建了一个公共void方法来切换到另一个布局，但每当我调用此方法时，应用程序崩溃。

logcat的：

Status _status = new Status {TotalRecs = query.Count};

            var progress = new Progress<Status>(msg => WriteStatusUpdate(msg));

            Task.Run(() =>
            {
                OrderablePartitioner<PayrollHeader> partitioner = Partitioner.Create(query, EnumerablePartitionerOptions.NoBuffering);
                Parallel.ForEach(partitioner, thisCheck =>
                {
                    lock (_status)
                    {
                        _status.ProcessMsg = "Voucher " + thisCheck.VoucherNumber;
                        _status.ProcessName = thisCheck.EmployeeName;
                        _status.CurrentRec = ++iChckNo;
                        dtSpan = DateTime.Now.Subtract(dtSpanStart);
                        _status.TimeMsg = string.Format("Elapsed {0}:{1}:{2}", dtSpan.Hours, dtSpan.Minutes, dtSpan.Seconds);
                    }

                    ((IProgress<Status>) progress).Report(_status);
                    thisCheck.GetDetails();
                });
            }).Wait();

 private void WriteStatusUpdate(Status _status)
    {
        lblVoucher.Text = _status.ProcessMsg;
        lblVoucher.Refresh();

        lblName.Text = _status.ProcessName;
        lblName.Refresh();

        lblCount.Text = string.Format("Records {0} of {1}", _status.CurrentRec, _status.TotalRecs);
        lblCount.Refresh();

        lblTime.Text = _status.TimeMsg;
        lblTime.Refresh();
    }

MainActivity：

07-05 16:35:22.823 14683-14712/com.example.name.mygame I/OpenGLRenderer: Initialized EGL, version 1.4

[ 07-05 16:35:24.724 14683:14754 D/]
HostConnection::get() New Host Connection established 0xae4b2240, tid 14754
07-05 16:35:28.500 14683-14754/com.example.name.mygame I/System.out: gameOverUi called!
-------- beginning of crash
07-05 16:35:28.558 14683-14754/com.example.name.mygame E/AndroidRuntime: FATAL EXCEPTION: Thread-218
Process: com.example.name.mygame, PID: 14683
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.Window.setContentView(int)' on a null object reference
at android.app.Activity.setContentView(Activity.java:2166)
at com.example.name.mygame.MainActivity.gameOverUi(MainActivity.java:15)
at com.example.name.mygame.GameView.gameOver(GameView.java:16)
at com.example.name.mygame.GameView.onDraw(GameView.java:188)
at com.example.name.mygame.GameLoopThread.run(GameLoopThread.java:37)
07-05 16:35:30.070 14683-14754/com.example.name.mygame I/Process: Sending signal. PID: 14683 SIG: 9

GameView类：

package com.example.name.mygame;

import android.app.Activity;
import android.os.Bundle;

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new GameView(this));
    }

    public void gameOverUi(){
        System.out.println("gameOverUi called!");
        setContentView(R.layout.gameover); //Crash here
    }
}

如何在不导致应用程序崩溃的情况下更改内容视图？任何答案都将不胜感激，谢谢。

Answer 1

MainActivity mActivity = new MainActivity();

这是你的问题。

这样您就可以创建一个MainActivity的新分配，但是您不能引用您的MainActivity。为此，您有一个零点异常。

避免这种情况。

Answer 2

您在MainActivity内没有正确地引用您的GameView课程，因为您当前正在创建新对象而没有获得对Activity的引用正在展示。这不是访问活动的正确方法。

由于Activity继承自Context，理论上你可以这样做：

public class GameView extends SurfaceView {
    private MainActivity mActivity;

    //Create new constructor to get the Activity
    public GameView(Activity activity) {
        super(activity);
        mActivity = (MainActivity) activity;
    }

    private void gameOver(){
        mActivity.gameOverUi();
    }
}

Android setContentView崩溃了我的应用程序

2 个答案: