Android - match_parent忽略layout_margin

Question

我的活动有一个LinearLayout单独的儿童视图.我希望两者都填满屏幕,减去12 dp的余量.

不幸的是,子视图被绘制为12 dp太大而被切断.显然在计算子视图的大小时match_parent忽略该layout_margin属性.解决这个问题最简单的方法是什么？

myActivity.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_margin="12dp"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">
    <com.myapp.myView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
    />
</LinearLayout>

myActivity.java

package com.myapp;

import android.app.Activity;
import android.os.Bundle;

public class myActivity extends Activity {


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.myActivity);
    }
}

myView.java

package com.myapp;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class myView extends View {

    private Paint paint = new Paint();

    public myView(Context context, AttributeSet attrs) {
        super(context, attrs);
        paint.setColor(0xFFFF0000); //red
        paint.setStyle(Paint.Style.STROKE); // for unfilled rectangles
        paint.setStrokeWidth(4);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int size = canvas.getWidth(); // width = height (see onMeasure())
        canvas.drawRect(0, 0, size, size, paint);   
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, widthMeasureSpec);
        // This gives us a square canvas!
    }
}

Answer 1

子视图可以有一个边距,父视图(或布局等视图组)可以在它们的边界和子视图之间有一个填充.换句话说,边距在视图之外,填充在内部.

另外,请看这个出色的解释:视图的填充和边距之间的差异

标准视图和填充而不是边距的示例:

我用标准视图而不是自定义视图创建了一个小例子,并使用上面建议的LinearLayout填充,它完美地工作(见截图):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="12dp"
    android:orientation="vertical" >

    <View
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:background="#ff0000"/>
</LinearLayout>

解

事实证明,问题是您canvas.getWidth()在自定义视图的onDraw方法中使用.使用视图getWidth()代替,解决了问题.最后:-)