我正在制作BMI计算器。在主要活动中，我有单选按钮来检查用户是否需要公制或英制。最近，我加入了一个计时器来确定用户何时完成打字以自动计算他们的BMI。英制计算工作得很好，但是当我点击公制单选按钮时，它会立即崩溃。错误消息“无法启动活动组件信息”。这种情况以前没有发生过。除了不同的测量值之外，代码应该非常相似。
感谢您的帮助！
以下是指标活动的代码：
public void performCalculation()
{
EditText weightET = (EditText) findViewById(R.id.weightET);
weightET.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
private Timer timer = new Timer();
private final long DELAY = 500;
@Override
public void afterTextChanged(final Editable editable)
{
timer.cancel();
timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run()
{
runOnUiThread(new Runnable() {
@Override
public void run()
{
calculate();
}
});
}
}, DELAY);
}
});
}
public void calculate()
{
EditText heightET = (EditText) findViewById(R.id.height);
EditText weightET = (EditText) findViewById(R.id.weight);
TextView yourBMI = (TextView) findViewById(R.id.yourBMI);
TextView bmiClass = (TextView) findViewById(R.id.bmiClass);
double height;
double weight;
double bmi;
double bmiRoundOff;
weight = Double.parseDouble(weightET.getText().toString());
height = Double.parseDouble(heightET.getText().toString());
bmi = (weight) / (height * height);
bmiRoundOff = Math.round(bmi * 100.00) / 100.00;
yourBMI.setText("Your BMI Is " + String.valueOf(bmiRoundOff));
if(bmiRoundOff < 18.5)
{
bmiClass.setText("Your BMI Class: Underweight");
}
if(bmiRoundOff > 18.5 && bmiRoundOff <= 24.9)
{
bmiClass.setText("Your BMI Class: Normal");
}
if(bmiRoundOff >= 25.0 && bmiRoundOff <= 29.0)
{
bmiClass.setText("Your BMI Class: Overweight!");
}
if(bmiRoundOff > 29.0)
{
bmiClass.setText("Your BMI Class: Obese");
}
}
以下是帝国活动的代码：
public void performCalculation()
{
EditText weightET = (EditText) findViewById(R.id.weightET);
weightET.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
private Timer timer = new Timer();
private final long DELAY = 500;
@Override
public void afterTextChanged(final Editable editable)
{
timer.cancel();
timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run()
{
runOnUiThread(new Runnable() {
@Override
public void run()
{
calculate();
}
});
}
}, DELAY);
}
});
}
public void calculate()
{
EditText weightET = (EditText) findViewById(R.id.weightET);
EditText feetET = (EditText) findViewById(R.id.feetET);
EditText inchesET = (EditText) findViewById(R.id.inchesET);
TextView yourBMI = (TextView) findViewById(R.id.yourBMI);
TextView bmiClass = (TextView) findViewById(R.id.bmiClass);
double feet;
double feetToInches;
double inches;
double totalInches;
double weight;
double bmi;
double bmiRoundOff;
weight = Double.parseDouble(weightET.getText().toString());
feet = Double.parseDouble(feetET.getText().toString());
inches = Double.parseDouble(inchesET.getText().toString());
feetToInches = feet * 12;
totalInches = feetToInches + inches;
bmi = (weight * 703) / (totalInches * totalInches);
bmiRoundOff = Math.round(bmi * 100.00) / 100.00;
yourBMI.setText("Your BMI Is " + String.valueOf(bmiRoundOff));
if(bmiRoundOff < 18.5)
{
bmiClass.setText("Your BMI Class: Underweight");
}
if(bmiRoundOff > 18.5 && bmiRoundOff <= 24.9)
{
bmiClass.setText("Your BMI Class: Normal");
}
if(bmiRoundOff >= 25.0 && bmiRoundOff <= 29.0)
{
bmiClass.setText("Your BMI Class: Overweight!");
}
if(bmiRoundOff > 29.0) {
bmiClass.setText("Your BMI Class: Obese");
}
}
public void main (View view)
{
Intent intent = new Intent(getApplicationContext() , MainActivity.class);
startActivity(intent);
}
以下是主要活动：
public void metric (View view)
{
Intent i = new Intent(getApplicationContext() , metric_activity.class);
startActivity(i);
}
public void imperial (View view)
{
Intent i = new Intent(getApplicationContext() , imperial_activity.class);
startActivity(i);
}
Logcat：
Process: com.jdaapps.bmicalculator, PID: 2004
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jdaapps.bmicalculator/com.jdaapps.bmicalculator.metric_activity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.jdaapps.bmicalculator.metric_activity.performCalculation(metric_activity.java:23)
at com.jdaapps.bmicalculator.metric_activity.onCreate(metric_activity.java:110)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
我认为如果你在mainActivity中可以做到这一点，那么你的活动没有得到：MainActivity.this.startActivity(intent)
如果你不知道哪个是主要在listview中发生的活动，你可以定义一个类扩展应用程序，并在清单中将其定义为应用程序名称，并在类（Activity currentActivity）和每个活动中有一个变量
在oncreat和onresume方法中执行此操作（例如，您的静态类是G）：G.currentActivity = this;
然后你可以像你一样在你想要的地方打电话：
G.currentActivity.startActivity(intent) ;