android - Android 中只显示一个 View

Question

我是 Android 新手。当我运行这段代码时，只显示一个圆圈。如果我删除 view1，则会显示 view2。但他们从来没有一起展示过!!!这是为什么？任何帮助将不胜感激。

谢谢

package com.dots;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;
public class Dots1Activity extends Activity
{
    private static final String TAG = "DotsActivity";
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LinearLayout ll = new LinearLayout(this);
        ll.setOrientation(LinearLayout.HORIZONTAL);
        TextView label = new TextView(this);
        LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(
             LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
        label.setText("Click the circle!");
        CustomDrawableView view1 = new CustomDrawableView(this, 100, 100, 50, Color.RED);
        CustomDrawableView view2 = new CustomDrawableView(this, 200, 200, 25, Color.GREEN);
        CustomDrawableView view3 = new CustomDrawableView(this, 300, 300, 10, Color.WHITE);
        ll.addView(label, layoutParams);
        ll.addView(view1, layoutParams);
        ll.addView(view2, layoutParams);
        ll.addView(view3, layoutParams);
        setContentView(ll);
    }

}

 class CustomDrawableView extends View implements OnClickListener{
     private Context context;
    private int x, y, radius, color;
    public CustomDrawableView(Context context, int x, int y, int radius, int color) {
        super(context);
        this.context = context;
        this.x = x;
        this.y =y;
        this.radius = radius;
        this.color = color;
        setOnClickListener(this);
    }

    protected void onDraw(Canvas canvas) 
    {
        super.onDraw(canvas);
        this.setBackgroundColor(Color.LTGRAY);
        Paint paint = new Paint (Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        canvas.drawCircle(x, y, radius, paint);

    }

    public void onClick(View v) {
        Toast.makeText(this.context, 
                x+"-"+y+"-"+radius, 
                Toast.LENGTH_SHORT).show();  
    }
}

Answer 1

ll.setOrientation(LinearLayout.HORIZONTAL);

它们并排放置。你看不到它们，因为你的显示器不是宽度为零。将它们放在 HorizontalScrollView 中或者使它们成为 VERTICAL。

---

我不确定这是否在这里生效，但我在 Android Documentation 上找到了这个:

Note that the framework will not draw views that are not in the invalid region. To force a view to draw, call invalidate().

试试这是否能解决您的问题(我猜是暂时的)。

---

关于您的代码

我注意到:onClickListener 的实现接口(interface)是 View.OnClickListener:

class CustomDrawableView extends View implements View.OnClickListener{ [...] }

如何解决问题

我查看了 Android 文档并找到了 this .他们提到了方法 onMeasure() ，其中:

Measure the view and its content to determine the measured width and the measured height.

所以我将它添加到您的自定义 CustomDrawableView 类中。不幸的是，您不能传递 super.onMeasure() 方法简单的整数，您需要先使用 View.MeasureSpec 对它们进行解码。 -类:

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){
        super.onMeasure(View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY),
                View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY));
    }

在示例中，我将宽度和高度都设置为 100px。另外，我对您的代码做了一些其他改进:

Dots1Activity 类

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.widget.LinearLayout;
import android.widget.TextView;

public class Dots1Activity extends Activity
{
    private static final String TAG = "DotsActivity";
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LinearLayout ll = new LinearLayout(this);
        ll.setOrientation(LinearLayout.VERTICAL);
        TextView label = new TextView(this);
        LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(
             LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
        label.setText("Click the circle!");
        CustomDrawableView view1 = new CustomDrawableView(this, 50, 50, 50, Color.RED);
        CustomDrawableView view2 = new CustomDrawableView(this, 75, 75, 25, Color.GREEN);
        CustomDrawableView view3 = new CustomDrawableView(this, 85, 85, 10, Color.WHITE);
        ll.addView(label, layoutParams);
        ll.addView(view1, layoutParams);
        ll.addView(view2, layoutParams);
        ll.addView(view3, layoutParams);
        setContentView(ll);
    }

}

CustomDrawableView 类

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.view.View;
import android.widget.Toast;

class CustomDrawableView extends View implements View.OnClickListener{
     private Context context;
    private int x, y, radius, color;
    public CustomDrawableView(Context context, int x, int y, int radius, int color) {
        super(context);
        this.context = context;
        this.x = x;
        this.y =y;
        this.radius = radius;
        this.color = color;
        setOnClickListener(this);
    }

    protected void onDraw(Canvas canvas) 
    {
        super.onDraw(canvas);
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        canvas.drawCircle(x, y, radius, paint);
    }

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){
        super.onMeasure(View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY),
                View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY));
    }

    public void onClick(View v) {
        Toast.makeText(this.context, 
                x+"-"+y+"-"+radius, 
                Toast.LENGTH_SHORT).show();  
    }
}

此代码可以编译，显示所有圆圈，并且 onClick-Event 也有效。

虽然我不得不说这是一个挑战，但我很感激。