Question

这是所有错误消息：

java.lang.RuntimeException: Unable to start activity ComponentInfo{johnny.newopen/johnny.newopen.easy}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(int)' on a null object reference
                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                            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 'void android.widget.TextView.setText(int)' on a null object reference
                                                            at johnny.newopen.easy.onCreate(easy.java:126)
                                                            at android.app.Activity.performCreate(Activity.java:6237)
                                                            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                            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)

以下是相关代码：

public class easy extends AppCompatActivity
{
 Button solve;
 private Chronometer chronometer;
 TextView plus1, plus2, minus1, minus2, multy1, multy2, points;
 int p1, p2, m1, m2, mu1, mu2, p, p_ans, m_ans, mu_ans;
 long time;
 private DBHelper mydb;
 boolean check, check1, check2, check3, check4;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_easy);
    mydb = new DBHelper(this);

 if (check1 && check2 && check3) {

        p = p + 60 - (int) time;
    }
    mydb.insertPoints(p);
    points = (TextView)findViewById(R.id.points);
    int x;
    try {
        {x = mydb.getPoints();}
    }
    catch (Exception e) {x=0;}
    points.setText(x);
}
}

我不断得到指向点的空指针。我在做什么错了？

Answer 1

好像在设置文本时TextView为null。查看您的代码（尚未完成），您的整数x尚未初始化。设置x = 0后尝试运行应用程序，还尝试检查textView的ID。
另外，您无法为textview设置整数值，请使用String.valueOf()

像这样：points.setText(String.valueOf(x))

很抱歉，答案格式不正确；我待会儿解决。

Answer 2

检查布局中TextView的ID是否与活动“（点）”中提到的ID相同。同样，您不能直接使用TextView将String.valueOf()设置为整数值。

points.setText(String.valueOf(x))

Answer 3

您可以使用x.toString（）设置“点”的文本值。但是您应该首先检查它是否存在，因为我认为您输入的TextView ID错误。

Answer 4

嘿，您不能直接将int设置为textview

简单地做

points.setText(""+x);

它将避免使用空指针。

或者如Anuj Kumar所说的那样

**points.setText(String.valueOf(x))**

我不断得到一个空指针

4 个答案: