Question

我是Java和Android的新手。我正在尝试创建一个计算圆柱体中液体体积的应用程序，然后将结果返回到textView框。但现在当我点击计算按钮时，它正在崩溃，我不知道我错过了什么。一切都很好。

package com.somename.fuel.volume.calculator;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.app.Activity;

public class CalculateCylinder extends Activity {

EditText length, width, height, depth;
TextView result;
Button calculate;
double firstNum, secNum, thirdNum, volume, area;
double liqVolume;
double radius;
double a, l, aSide,aTop,b,Arc,FluidSurfaceAreaTotal,r,d,v,h,fsal;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.calculate_cylinder);

    calculate = (Button) findViewById(R.id.buttonCylCalc);

    length = (EditText) findViewById(R.id.editCylLength);
    height = (EditText) findViewById(R.id.editCylHeight);
    depth = (EditText) findViewById(R.id.editCylDepth);
    result = (TextView) findViewById(R.id.buttonCylResult);

    calculate.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            //Toast.makeText(getApplicationContext(), (CharSequence) result, Toast.LENGTH_LONG).show();
            try {
                calculate();
            } catch (Exception e) {
                e.printStackTrace();
            }
            result.setText((CharSequence) result);
        }

        public TextView calculate() throws Exception {
            // TODO Auto-generated method stub
            double firstNum = Double.valueOf(length.getText().toString());
            double secNum   = Double.valueOf(height.getText().toString());
            double thirdNum = Double.valueOf(depth.getText().toString());

            radius = (secNum/2);
            area = ((secNum*secNum)*3.14);
            //liqVolume = (firstNum) * (radius*radius)(acos(radius-depth/radius))
            // Cubic Volume

            v = aSide * l;
            // Fluid surface Area, Side
            aSide = (r*r)*(3.14 / 2 -Math.acos(1-h/r)) - (r-h)*Math.sqrt(h*(2*r-h));
            // Fluid Surface Area Top
            aTop = 2*Math.sqrt((r*r)-((r-h)*(r-h) * l));
            // Fluid Surface Area Bottom
            b = fsal*l;
            // Fluid Surface Area Total
            FluidSurfaceAreaTotal = 2*aSide+aTop+b;
            // Cylinder Radius
            r = d/2;
            // Cylinder Diameter
            d = 2*r;
            if (h <= r )
                // Fluid Side Arc Length
                fsal = 2*r*Math.acos((r-h)/r);

            else if (h > r)
                fsal = 2*r*(3.14-Math.acos((h-r)/r));
            return result;
            }


    });
}   

}

这是一个logcat：

10-18 05:24:38.893: E/AndroidRuntime(964): FATAL EXCEPTION: main
10-18 05:24:38.893: E/AndroidRuntime(964): java.lang.ClassCastException:    android.widget.Button
10-18 05:24:38.893: E/AndroidRuntime(964):  at   com.dbryant423.fuel.volume.calculator.CalculateCylinder$1.onClick(CalculateCylinder.java:55 )
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.view.View.performClick(View.java:2408)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.view.View$PerformClick.run(View.java:8816)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.os.Handler.handleCallback(Handler.java:587)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.os.Handler.dispatchMessage(Handler.java:92)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.os.Looper.loop(Looper.java:123)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.app.ActivityThread.main(ActivityThread.java:4627)
10-18 05:24:38.893: E/AndroidRuntime(964):  at java.lang.reflect.Method.invokeNative(Native Method)
10-18 05:24:38.893: E/AndroidRuntime(964):  at java.lang.reflect.Method.invoke(Method.java:521)
10-18 05:24:38.893: E/AndroidRuntime(964):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-18 05:24:38.893: E/AndroidRuntime(964):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-18 05:24:38.893: E/AndroidRuntime(964):  at dalvik.system.NativeStart.main(Native Method)

我一直在绞尽脑汁试图弄清楚如何对此进行数学计算，而我却无法找到解决原因的原因。我确定这可能是我在某处遗漏的简单事情。如果您需要其他文件中的更多信息，请告诉我，但这个问题似乎是唯一存在问题的信息。我也知道我还没有删除未使用的变量。

Answer 1

result.setText((CharSequence) result);

此行导致例外，因为您要将Android View类投射到CharSequence类。

可能的解决方案：

将方法public TextView calculate()的返回类型更改为

public String calculate()

现在方法public String calculate() 返回结果字符串 fsal

你的按钮Click()就像，

calculate.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            // TODO Auto-generated method stub
            //Toast.makeText(getApplicationContext(), (CharSequence) result, Toast.LENGTH_LONG).show();
           String resultValue = "";
            try {
             resultValue =  calculate();
            } catch (Exception e) {
                e.printStackTrace();
            }
            result.setText( resultValue);
        }

Answer 2

result = (TextView) findViewById(R.id.buttonCylResult);

你是否正确投射？根据命名，我会说你是从一个按钮转换到TextView。尝试更改为，

result = (Button) findViewById(R.id.buttonCylResult);

android.widget.Button中的致命异常

2 个答案: