如何在Android/Java程序中执行同一级别的If语句？

Question

目前，我将介绍给我们一个名为PaintPot的Android程序的代码，该程序允许用户在他们的Android设备上进行手指绘画。

该代码处理时，点击屏幕，按钮被点击会发生的事件等

// Here is the event dispatcher for our app. We need to Override the method for the Form 
// superclass 
@Override 
public boolean dispatchEvent(Component component, String id, String eventName, 
          Object[] args) { 

    //if the canvas is touched by a tapping finger 
    if (component.equals(myCanvas) && eventName.equals("Touched")) { 
     canvasTouced(((Float) args[0]).intValue(), ((Float) args[1]).intValue()); 
     return true; 

     //if the canvas is touched by a dragging finger, paint the line this way 
    } else if (component.equals(myCanvas) && eventName.equals("Dragged")) { 
     drawLine(((Float) args[2]).intValue(), 
       ((Float) args[3]).intValue(), 
       ((Float) args[4]).intValue(), 
       ((Float) args[5]).intValue()); 
     return true; 

     //if the canvas is touched while the blue button is selected 
    } else if (component.equals(btnBlue) && eventName.equals("Click")) { 
     myCanvas.PaintColor(COLOR_BLUE); 
     return true; 

     //if the canvas is touched while the green button is selected 
    } else if (component.equals(btnGreen) && eventName.equals("Click")) { 
     myCanvas.PaintColor(COLOR_GREEN); 
     return true; 

     //if the canvas is touched while the red button is selected 
    } else if (component.equals(btnRed) && eventName.equals("Click")) { 
     myCanvas.PaintColor(COLOR_RED); 
     return true; 

     //if the wipe button is selected 
    } else if (component.equals(btnWipe) && eventName.equals("Click")) { 
     myCanvas.Clear(); 
     return true; 
    } 


    return false; 
} 

的代码工作正常，我想要做什么它“原样”。但是我不明白的是，如果用户在画布上轻敲或拖动他或她的手指的if语句处于“同一级别”，或者如果选择了颜色按钮，则在if语句中。不应该是当用户在屏幕上点击或拖动他的手指时，相同的代码会确定制作的线条或点是否也应该询问线条或点应该是什么颜色，而不仅仅是尺寸点，取决于选择了哪种颜色的按钮？

为了更完整的参考，这里是整个代码，如果有人好奇：

import android.graphics.Color; 
import com.google.devtools.simple.runtime.components.android.Button; 
import com.google.devtools.simple.runtime.components.Component; 
import com.google.devtools.simple.runtime.components.HandlesEventDispatching; 
import com.google.devtools.simple.runtime.components.android.Canvas; 
import com.google.devtools.simple.runtime.components.android.Form; 
import com.google.devtools.simple.runtime.components.android.HorizontalArrangement; 
import com.google.devtools.simple.runtime.components.android.Label; 
import com.google.devtools.simple.runtime.events.EventDispatcher; 


import java.util.Random; 




public class PaintPotActivity extends Form implements HandlesEventDispatching { 


private Canvas myCanvas; //creates a canvas object 
private Label lblStatus; //creates a label that discusses the status of the program 
private Button btnRed; //creates a button for red paint 
private Button btnBlue; // "" for blue paint 
private Button btnGreen; // "" for green paint 


private Button btnWipe; //creates a button that wipes the screen clean 
private Button btnDotSize; // creates a button that changes the dot size 




// Variable (field) used to for displaying number of touches 
int numTouches; //declares an integer that lists out the number of touches a user made 


// The equivalent to a "main" method for App Inventor apps is the $define method. 
void $define() { 


    //We are going to place the color buttons in a HorizontalArrangement 
    HorizontalArrangement hr = new HorizontalArrangement(this); 
    btnRed = new Button(hr); 
    btnBlue = new Button(hr); 
    btnGreen = new Button(hr); 


    //set their color 
    btnRed.BackgroundColor(Color.RED); 
    btnBlue.BackgroundColor(Color.BLUE); 
    btnGreen.BackgroundColor(Color.GREEN); 

    //set the button text 
    btnRed.Text("Red"); 
    btnBlue.Text("Blue"); 
    btnGreen.Text("Green"); 


    //canvas into its own HorizontalArrangement 
    hr = new HorizontalArrangement(this); 
    myCanvas = new Canvas(hr); 
    myCanvas.Width(400); 
    myCanvas.Height(400); 
    myCanvas.LineWidth(10); 


    //Wipe and a label into its own HorizontalArrangement 
    hr = new HorizontalArrangement(this); 
    btnWipe = new Button(hr); 
    btnWipe.Text("Wipe"); 


    lblStatus = new Label(hr); 
    lblStatus.Text(" touchX/touchY:"); 


    // Register for events. By the second argument can be any string. The third argument must 
    // exactly match the name of the event that you want to handle for that component. When the event 
    // happens, dispatchEvent will be called with these arguments. 
    EventDispatcher.registerEventForDelegation(this, "JavaBridge", "Touched"); 
    EventDispatcher.registerEventForDelegation(this, "JavaBridge", "Click"); 
    EventDispatcher.registerEventForDelegation(this, "JavaBridge", "Dragged"); 
} 


// Here is the event dispatcher for our app. We need to Override the method for the Form 
// superclass 
@Override 
public boolean dispatchEvent(Component component, String id, String eventName, 
          Object[] args) { 

    //if the canvas is touched by a tapping finger 
    if (component.equals(myCanvas) && eventName.equals("Touched")) { 
     canvasTouced(((Float) args[0]).intValue(), ((Float) args[1]).intValue()); 
     return true; 

     //if the canvas is touched by a dragging finger, paint the line this way 
    } else if (component.equals(myCanvas) && eventName.equals("Dragged")) { 
     drawLine(((Float) args[2]).intValue(), 
       ((Float) args[3]).intValue(), 
       ((Float) args[4]).intValue(), 
       ((Float) args[5]).intValue()); 
     return true; 

     //if the canvas is touched while the blue button is selected 
    } else if (component.equals(btnBlue) && eventName.equals("Click")) { 
     myCanvas.PaintColor(COLOR_BLUE); 
     return true; 

     //if the canvas is touched while the green button is selected 
    } else if (component.equals(btnGreen) && eventName.equals("Click")) { 
     myCanvas.PaintColor(COLOR_GREEN); 
     return true; 

     //if the canvas is touched while the red button is selected 
    } else if (component.equals(btnRed) && eventName.equals("Click")) { 
     myCanvas.PaintColor(COLOR_RED); 
     return true; 

     //if the wipe button is selected 
    } else if (component.equals(btnWipe) && eventName.equals("Click")) { 
     myCanvas.Clear(); 
     return true; 
    } 


    return false; 
} 




/** 
* This method will get the touched touchX, touchY coordinates and will then create a circle 
* of random radius (between 1 to 33) with the color that was selected (RED, BLUE or GREEN). 
* It will also display the touched touchX,touchY coordinates. 
* @param x current x 
* @param y current y 
*/ 
private void canvasTouced(int x, int y) { 


    myCanvas.DrawCircle(x, y, new Random().nextInt(33)); 
    lblStatus.Text(" touchX/touchY:" + x + "/" + y + " touches: " + ++numTouches); 


} 


/** 
* Method to draw line 
* @param prevX last touch x 
* @param prevY last touch y 
* @param touchX current x 
* @param touchY current y 
*/ 
private void drawLine(int prevX, int prevY, int touchX, int touchY) { 
    myCanvas.DrawLine(prevX, prevY, touchX, touchY); 
} 


} 

Answer 1

dispatchEvent被称为应用程序触发事件。单击每个按钮并与应用程序进行交互时会引发单独的事件。每个if语句都确定如何处理不同类型的事件。

不应该是当用户在屏幕上点击或拖动他的手指时，确定制作的线或点是否也应该询问线或点应该是什么颜色的相同代码，而不仅仅是点的大小，取决于选择什么颜色的按钮

在这种情况下，事件之间的状态被保存在myCanvas - 点击btnBlue设置油漆颜色为蓝色画布（myCanvas.PaintColor(COLOR_BLUE);）上，然后等待另一个事件发生。如果用户拖过画布，则绘制一条线（最终为myCanvas.DrawLine(prevX, prevY, touchX, touchY);）。由于myCanvas记得该状态，因此它将以蓝色绘制线条。

Answer 2

如果语句如果用户点击或跨 拖动他或她的手指在画布上同级别

好吧，我可能是错的，但如果由the same level你的意思是某种平等权重的用户的行动，那么答案是肯定的。

它不应该是当用户点击或拖动他的整个 屏幕上的手指，决定是否行或由点 也应该问什么颜色的线或点应在同一代码而不是 只是大小的点，取决于选择了哪种颜色的按钮

是的，它应该。为此，您将不得不相应编程。

Answer 3

这是事件处理的常见构造。这可能有助于将“同级别”IF视为用户可以选择的选项。当您在同一个对话框上有两个按钮时，通常不会嵌套它们，因为您无法知道哪个按钮会被点击。

该方法的名称'dispatchEvent'是一个很大的线索，它所做的只是接收事件并选择适当的代码路径。通常，每个IF只是转过身来调用一个函数或方法，否则调度方法可能会变得很大。

如果你对所有可能的消息都有足够大的枚举（Win32做到这一点），你可以用'switch/case'语句而不是所有的IF来做同样的事情。