Question

当我添加此行时，不知道为什么会发生这种情况，它开始崩溃应用程序：

    total = total + add;
    tvMoney.setText("Your Total is $" + total);

以下是代码的完整部分，当我删除（或注释掉）上述代码时，它可以正常工作。应用程序应该更新一个部分，同时还更新具有总计的另一个文本。

// What happens when the "+" button is pressed.
public void sendAdd(View view) {
    llMoney = (LinearLayout) findViewById(R.id.llMoney);
    etMoney = (EditText) findViewById(R.id.etMoney);
    String message = etMoney.getText().toString();
    if (message == null || message.isEmpty()){
        add = 0.0;
    } else {
        add = Double.parseDouble(etMoney.getText().toString());
    }

    total = total + add;
    tvMoney.setText("Your Total is $" + total);     

    TextView text = new TextView(this);
    text.setText("You've added money! + " + message);
    text.setTextSize(20);
    text.setTextColor(Color.GREEN);
    text.setGravity(Gravity.RIGHT);
    llMoney.addView(text);

以下是变量声明：

//declaring items
LinearLayout llNotes, llMoney;
Button butNotes, butAdd, butSub;
EditText etNotes, etMoney;
TextView tvMoney;

//To update the total amount of money variable
double total, add, sub;

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

    total = 0.0;
    add = 0.0;
    sub = 0.0;

logcat的

05-11 17:54:20.477: D/AndroidRuntime(23918): Shutting down VM
05-11 17:54:20.477: W/dalvikvm(23918): threadid=1: thread exiting with uncaught exception (group=0x4145c360)
05-11 17:54:20.497: E/AndroidRuntime(23918): FATAL EXCEPTION: main
05-11 17:54:20.497: E/AndroidRuntime(23918): java.lang.IllegalStateException: Could not execute method of the activity
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.view.View$1.onClick(View.java:3690)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.view.View.performClick(View.java:4192)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.view.View$PerformClick.run(View.java:17254)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.os.Handler.handleCallback(Handler.java:615)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.os.Handler.dispatchMessage(Handler.java:92)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.os.Looper.loop(Looper.java:137)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.app.ActivityThread.main(ActivityThread.java:4950)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at java.lang.reflect.Method.invokeNative(Native Method)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at java.lang.reflect.Method.invoke(Method.java:511)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at dalvik.system.NativeStart.main(Native Method)
05-11 17:54:20.497: E/AndroidRuntime(23918): Caused by: java.lang.reflect.InvocationTargetException
05-11 17:54:20.497: E/AndroidRuntime(23918):    at java.lang.reflect.Method.invokeNative(Native Method)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at java.lang.reflect.Method.invoke(Method.java:511)
05-11 17:54:20.497: E/AndroidRuntime(23918):    at android.view.View$1.onClick(View.java:3685)
05-11 17:54:20.497: E/AndroidRuntime(23918):    ... 11 more
05-11 17:54:20.497: E/AndroidRuntime(23918): Caused by: java.lang.NullPointerException
05-11 17:54:20.497: E/AndroidRuntime(23918):    at net.tagyoureit.heykeepup.MainActivity.sendAdd(MainActivity.java:123)
05-11 17:54:20.497: E/AndroidRuntime(23918):    ... 14 more

Answer 1

你没有初始化tvMoney。

如果你没有初始化一个成员变量（比如tvMoney）你的代码会编译，但你在运行时会遇到问题。

Answer 2

您似乎没有在任何地方实例化您的tvMoney变量，如下所示：

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

tvMoney = (TextView) findViewById(R.id.tvMoney);

total = 0.0;
add = 0.0;
sub = 0.0;

Answer 3

when I added this line it started crashing the app:

当您尝试设置文本时，

tvMoney为空。您需要在访问之前找到TextView的实例。我相信TextView中的tvMoney ID为Activity layout，然后更改

tvMoney = (EditText) findViewById(R.id.tvMoney);

tvMoney.setText("Your Total is $" + total);

使用两个setText而不是一个时，应用程序崩溃

3 个答案: