Question

我的应用程序出现问题，因为它总是崩溃，但我不确定如何修复它。任何帮助将不胜感激。我对android studio仍然缺乏经验，因此试图寻找解决方案。

这是崩溃的logcat：

10-12 02:11:37.457    7223-7223/com.fluke.kgwee.test E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.fluke.kgwee.test, PID: 7223
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.fluke.kgwee.test/com.fluke.kgwee.test.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
        at android.app.ActivityThread.-wrap11(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
        at android.app.Activity.findViewById(Activity.java:2090)
        at com.fluke.kgwee.test.MainActivity.<init>(MainActivity.java:17)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)

Java文件：

public class MainActivity extends AppCompatActivity {

Button buttonStart;
TextView textCounter = (TextView) findViewById(R.id.counter);

MyCountDownTimer myCountDownTimer = new MyCountDownTimer(30000, 1000, textCounter);

public MainActivity() {
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);

    buttonStart = (Button) findViewById(R.id.start);

    buttonStart.setOnClickListener(new OnClickListener() {



        @Override
        public void onClick(View v) {
            myCountDownTimer.start();

            new CountDownTimer(30000, 1000) {

                public void onTick(long millisUntilFinished) {
                    textCounter.setText("seconds remaining: " + millisUntilFinished / 1000);
                }

                public void onFinish() {
                    textCounter.setText("done!");
                }
            }.start();
        }


    });

}

public class MyCountDownTimer extends CountDownTimer {

    private TextView textCounter;

    public MyCountDownTimer(long millisInFuture, long countDownInterval, TextView textCounter) {
        super(millisInFuture, countDownInterval);
        this.textCounter = textCounter;
    }

    @Override
    public void onTick(long millisUntilFinished) {
        this.textCounter.setText(millisUntilFinished / 1000l + " seconds remaining : ");

    }

    @Override
    public void onFinish() {
        this.textCounter.setText("Finished");

    }

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

}

Answer 1

TextView textCounter = (TextView) findViewById(R.id.counter);

将上面的行放在setContentView之后。在设置内容视图之前，您无法访问布局的项目。

空对象引用：应用程序崩溃

1 个答案: