java - Android studio 改变 Intent 时崩溃

Question

程序应该像这样工作，有一个计时器和显示的图片，使用名为“Age 10-11”的底部应该将用户切换到另一个具有相同计时器设置的屏幕，但显示不同的图片。问题是当涉及到代码的 Intent 部分时它崩溃了。如果第二个 Activity 类只有默认代码，它可以正常工作，但是当从 Activity 1 添加相同的代码时，它会崩溃。消息“不幸的是，程序已停止工作”添加日志

公共(public)类 Age_7_to_9 扩展 Activity 实现 OnClickListener{

private CountDownTimer countDownTimer;
private boolean timerHasStarted = false;
private Button StartB;
private Button NextB;
public TextView text;
private final long startTime = 30* 1000;
private final long interval = 1* 1000;

ImageView imageView1;
int len=images.length-1;
static int curr=0;


@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_age_7_to_9);

    imageView1=(ImageView)findViewById(R.id.imageView);


    StartB = (Button) this.findViewById(R.id.button);
    NextB = (Button) this.findViewById(R.id.tenEleven);
    StartB.setOnClickListener(this);
    NextB.setOnClickListener(this);
    text = (TextView) this.findViewById(R.id.timer);
    countDownTimer = new MyCountDownTimer(startTime, interval);
    text.setText(text.getText() + String.valueOf(startTime / 1000));
}




private static final int[] images=new int[]     {R.drawable.p,R.drawable.pp,};
@Override
public void onClick(View v)
{
    switch (v.getId())
    {
        case R.id.button:
            if(curr < 2)
            {
                imageView1.setImageResource(images[curr]);
            }
            else
            {
                curr=-1;
            }
            curr++;

            if(!timerHasStarted)
            {
                countDownTimer.start();
                timerHasStarted = true;
                StartB.setText("STOP");

            }
            else
            {
                countDownTimer.cancel();
                timerHasStarted = false;
                StartB.setText("RESTART");

                Log.i("MyActivity", "MyClass.getView() — get item number " + curr);
            }
            break;
        case R.id.tenEleven:
            Intent i = new Intent(this, Age_10_to_11.class);
            startActivity(i);
            break;
    }
}




public class MyCountDownTimer extends CountDownTimer
{
    public MyCountDownTimer(long startTime, long interval)
    {
        super(startTime, interval);
    }
    @Override
    public void onFinish()
    {
        text.setText("Time's Up!");
    }

    @Override
    public void onTick(long millisUntilFinished)
    {
        text.setText(""+ millisUntilFinished / 1000);
    }
}

@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_age_7_to_9, 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);
}

}

XML 代码

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".Age_7_to_9"
    android:background="@drawable/backgroundimage">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start"
        android:id="@+id/button"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="99dp" />

    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Age 10-11"
        android:id="@+id/tenEleven"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:onClick="onClick"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:id="@+id/timer"
        android:layout_above="@+id/button"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="51dp" />

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView"
        android:layout_above="@+id/timer"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="50dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Highscore:"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="0"
        android:id="@+id/textView2"
        android:layout_alignTop="@+id/textView4"
        android:layout_alignRight="@+id/tenEleven"
        android:layout_alignEnd="@+id/tenEleven" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Counter:"
        android:id="@+id/textView3"
        android:layout_alignTop="@+id/textView2"
        android:layout_toRightOf="@+id/button"
        android:layout_toEndOf="@+id/button" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="0"
        android:id="@+id/textView4"
        android:layout_alignTop="@+id/textView"
        android:layout_toLeftOf="@+id/button"
        android:layout_toStartOf="@+id/button" />

</RelativeLayout>

登录下方

04-29 10:29:00.390    2198-2198/com.example.daniel.pmp E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.daniel.pmp, PID: 2198
java.lang.RuntimeException: Unable to start activity    ComponentInfo{com.example.daniel.pmp/com.example.daniel.pmp.Age_10_to_11}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.widget.TextView.getText()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
        at android.app.ActivityThread.access$800(ActivityThread.java:144)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        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:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.widget.TextView.getText()' on a null object reference
            at com.example.daniel.pmp.Age_10_to_11.onCreate(Age_10_to_11.java:46)
            at android.app.Activity.performCreate(Activity.java:5937)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            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:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Answer 1

如果没有看到 Logcat，就很难知道，但是如果我查看你的代码，我会发现这里出了一些问题。不知道这是否只是复制/粘贴错误。

您正在初始化len，然后再初始化图像:

int len=images.length-1;

之后您将初始化图像:

private static final int[] images=new int[]     {R.drawable.p,R.drawable.pp,};

这是行不通的，如果图像未初始化，您将无法获得长度。这导致我们犯了第二个错误:

您的图像数组在列表末尾有一个逗号:

 {R.drawable.p,R.drawable.pp,} <-- that could not work.

此外，您在这里使用了错误的参数:

    case R.id.tenEleven:
            Intent i = new Intent(this, Age_10_to_11.class);
            startActivity(i);
            break;

必须是Age_7_to_9.this，而不是“this”:

     case R.id.tenEleven:
            Intent i = new Intent(Age_7_to_9.this, Age_10_to_11.class);
            startActivity(i);
            break;

否则您将引用 OnClickListener。

由于这三个错误，通常您的应用程序无法编译。但我猜导致您崩溃的原因是您没有将 Age_10_to_11 Activity 添加到您的 list 中。但要准确了解它，您必须发布您的 logcat...