自定义控件——视图的构建过程——视图的测量方法

逃离我推掉我的手 2024-04-07 12:36 58阅读 0赞

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对于wrap\_content形式的宽高，App需要测量它们的实际长度，需要测量的实体主要有3种：

(1)文本尺寸测量文本尺寸分为文本的宽度和高度，需根据文本大小分别计算。

(2)图形尺寸测量如果图形是Bitmap格式，就调用getWidth和getHeight方法；如果图形是Drawable格式，就调用getIntrinsicWidth和getIntrinsicHeight方法。

(3)布局尺寸测量调用measure方法按照测量规格进行测量操

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文本尺寸的测量

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代码：

package com.example.myapplication;
    
    import androidx.appcompat.app.AppCompatActivity;
    import android.os.Bundle;
    import android.util.TypedValue;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.ArrayAdapter;
    import android.widget.Spinner;
    import android.widget.TextView;
    import com.example.myapplication.util.MeasureUtil;
    
    public class MainActivity extends AppCompatActivity
    {
        private TextView tv_desc, tv_text;
    
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
    
            tv_desc = findViewById(R.id.tv_desc);
            tv_text = findViewById(R.id.tv_text);
    
    
            initSizeSpinner(); // 初始化文字大小的下拉框
        }
    
        // 初始化文字大小的下拉框
        private void initSizeSpinner()
        {
            ArrayAdapter<String> sizeAdapter = new ArrayAdapter<String>(this, R.layout.item_select, descArray);
    
            Spinner sp_size = findViewById(R.id.sp_size);
            sp_size.setPrompt("请选择文字大小");
            sp_size.setAdapter(sizeAdapter);
            sp_size.setOnItemSelectedListener(new SizeSelectedListener());
            sp_size.setSelection(0);
    
        }
    
        private String[] descArray = {"12sp", "15sp", "17sp", "20sp", "22sp", "25sp", "27sp", "30sp"};
    
        private int[] sizeArray = {12, 15, 17, 20, 22, 25, 27, 30};
    
        class SizeSelectedListener implements AdapterView.OnItemSelectedListener
        {
    
    
            public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3)
            {
    
                String text = tv_text.getText().toString();
    
                int textSize = sizeArray[arg2];
    
                tv_text.setTextSize(TypedValue.COMPLEX_UNIT_SP, textSize);
    
                // 计算获取指定文本的宽度(其实就是长度)
                int width = (int) MeasureUtil.getTextWidth(text, textSize);
    
                // 计算获取指定文本的高度
                int height = (int) MeasureUtil.getTextHeight(text, textSize);
    
                String desc = String.format("下面文字的宽度是%d，高度是%d", width, height);
    
                tv_desc.setText(desc);
            }
    
            public void onNothingSelected(AdapterView<?> arg0) {}
    
        }
    
    }

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MeasureUtil

package com.example.myapplication.util;
    
    import android.app.Activity;
    import android.graphics.Paint;
    import android.graphics.Paint.FontMetrics;
    import android.text.TextUtils;
    import android.view.View;
    import android.view.View.MeasureSpec;
    import android.view.ViewGroup;
    import android.view.ViewGroup.LayoutParams;
    import android.widget.LinearLayout;
    
    public class MeasureUtil 
    {
    
        // 获取指定文本的宽度(其实就是长度)
        public static float getTextWidth(String text, float textSize) 
        {
            if (TextUtils.isEmpty(text)) 
            {
                return 0;
            }
            
            Paint paint = new Paint(); // 创建一个画笔对象
            paint.setTextSize(textSize); // 设置画笔的文本大小
            return paint.measureText(text); // 利用画笔丈量指定文本的宽度
        }
    
        // 获取指定文本的高度
        public static float getTextHeight(String text, float textSize) 
        {
            Paint paint = new Paint(); // 创建一个画笔对象
            paint.setTextSize(textSize); // 设置画笔的文本大小
            FontMetrics fm = paint.getFontMetrics(); // 获取画笔默认字体的度量衡
            return fm.descent - fm.ascent; // 返回文本自身的高度
            //return fm.bottom - fm.top + fm.leading;  // 返回文本所在行的行高
        }
    
        // 根据资源编号获得线性布局的实际高度(页面来源)
        public static float getRealHeight(Activity act, int resid) 
        {
            LinearLayout llayout = act.findViewById(resid);
            return getRealHeight(llayout);
        }
    
        // 根据资源编号获得线性布局的实际高度(视图来源)
        public static float getRealHeight(View parent, int resid)
        {
            LinearLayout llayout = parent.findViewById(resid);
            return getRealHeight(llayout);
        }
    
        // 计算指定线性布局的实际高度
        public static float getRealHeight(View child) 
        {
            LinearLayout llayout = (LinearLayout) child;
            
            // 获得线性布局的布局参数
            LayoutParams params = llayout.getLayoutParams();
            
            if (params == null) 
            {
                params = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
            }
            
            // 获得布局参数里面的宽度规格
            int wdSpec = ViewGroup.getChildMeasureSpec(0, 0, params.width);
            
            int htSpec;
            
            if (params.height > 0) { // 高度大于0，说明这是明确的dp数值
                // 按照精确数值的情况计算高度规格
                htSpec = MeasureSpec.makeMeasureSpec(params.height, MeasureSpec.EXACTLY);
            } else { // MATCH_PARENT=-1，WRAP_CONTENT=-2，所以二者都进入该分支
                // 按照不确定的情况计算高度规则
                htSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
            }
            llayout.measure(wdSpec, htSpec); // 重新丈量线性布局的宽高
            // 获得并返回线性布局丈量之后的高度。调用getMeasuredWidth方法可获得宽度
            return llayout.getMeasuredHeight();
        }
    
    }

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代码：

package com.example.myapplication;
    
    import androidx.appcompat.app.AppCompatActivity;
    import android.os.Bundle;
    import android.widget.LinearLayout;
    import android.widget.TextView;
    import com.example.myapplication.util.MeasureUtil;
    
    public class MainActivity extends AppCompatActivity
    {
    
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
    
            LinearLayout ll_header = findViewById(R.id.ll_header);
    
            TextView tv_desc = findViewById(R.id.tv_desc);
    
            // 计算获取线性布局的实际高度
            float height = MeasureUtil.getRealHeight(ll_header);
    
            String desc = String.format("上面下拉刷新头部的高度是%f", height);
    
            tv_desc.setText(desc);
        }
    }

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MeasureUtil

package com.example.myapplication.util;
    
    import android.app.Activity;
    import android.graphics.Paint;
    import android.graphics.Paint.FontMetrics;
    import android.text.TextUtils;
    import android.view.View;
    import android.view.View.MeasureSpec;
    import android.view.ViewGroup;
    import android.view.ViewGroup.LayoutParams;
    import android.widget.LinearLayout;
    
    public class MeasureUtil
    {
    
        // 获取指定文本的宽度(其实就是长度)
        public static float getTextWidth(String text, float textSize)
        {
            if (TextUtils.isEmpty(text))
            {
                return 0;
            }
    
            Paint paint = new Paint(); // 创建一个画笔对象
            paint.setTextSize(textSize); // 设置画笔的文本大小
            return paint.measureText(text); // 利用画笔丈量指定文本的宽度
        }
    
        // 获取指定文本的高度
        public static float getTextHeight(String text, float textSize)
        {
            Paint paint = new Paint(); // 创建一个画笔对象
            paint.setTextSize(textSize); // 设置画笔的文本大小
            FontMetrics fm = paint.getFontMetrics(); // 获取画笔默认字体的度量衡
            return fm.descent - fm.ascent; // 返回文本自身的高度
            //return fm.bottom - fm.top + fm.leading;  // 返回文本所在行的行高
        }
    
        // 根据资源编号获得线性布局的实际高度(页面来源)
        public static float getRealHeight(Activity act, int resid)
        {
            LinearLayout llayout = act.findViewById(resid);
            return getRealHeight(llayout);
        }
    
        // 根据资源编号获得线性布局的实际高度(视图来源)
        public static float getRealHeight(View parent, int resid)
        {
            LinearLayout llayout = parent.findViewById(resid);
            return getRealHeight(llayout);
        }
    
        // 计算指定线性布局的实际高度
        public static float getRealHeight(View child)
        {
            LinearLayout llayout = (LinearLayout) child;
    
            // 获得线性布局的布局参数
            LayoutParams params = llayout.getLayoutParams();
    
            if (params == null)
            {
                params = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
            }
    
            // 获得布局参数里面的宽度规格
            int wdSpec = ViewGroup.getChildMeasureSpec(0, 0, params.width);
    
            int htSpec;
    
            if (params.height > 0) { // 高度大于0，说明这是明确的dp数值
                // 按照精确数值的情况计算高度规格
                htSpec = MeasureSpec.makeMeasureSpec(params.height, MeasureSpec.EXACTLY);
            } else { // MATCH_PARENT=-1，WRAP_CONTENT=-2，所以二者都进入该分支
                // 按照不确定的情况计算高度规则
                htSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
            }
            llayout.measure(wdSpec, htSpec); // 重新丈量线性布局的宽高
            // 获得并返回线性布局丈量之后的高度。调用getMeasuredWidth方法可获得宽度
            return llayout.getMeasuredHeight();
        }
    
    }

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