Android學習之旅(4)----自定義View

自定義View

當Android提供的View不能滿足我們的開發需求時，我們可以通過繼承View來實現自定義組件。一般情況下可以重寫以下方法：

• 構造函數
  需要通過構造函數告訴編譯器，組件依賴在那個父窗體上。
• onFinishInflate
  回調方法，當應用從XML佈局文件加載該組件並利用它構建界面時，該方法被回調
• onMeasure(int,int)
  調用該方法來檢測View組件以及其所包含的所有子組件的大小
• onLayout(boolean,int,int,int,int)
  當該組件需要分配其子組件的位置、大小時，該方法就會被回調
• onSizeChanged(int,int,int,int)
  當該組件的大小被改變時回調該方法
• onDraw(Canvas)
  當組件將被繪製時觸發該方法
• onKeyDown(int,keyEvent)
  當某個件被按下時觸發該方法
• onKeyUp(int,keyEvent)
  當鬆開某個鍵時觸發該方法
• onTrackballEvent(MotionEvent)
  當發生估計求事件時觸發該方法
• onTouchEvent(MotionEvent)
  當發生觸摸屏事件時觸發該方法
• onFocusChanged(boolean,int,Rect)
  當該組件的發生改變時觸發該方法
• onWindowFocusChanged(boolean)
  當包含該組件的窗口失去獲得到焦點時觸發該方法
• onAttachedToWindow()
  當把該組件放在某個窗口時觸發該方法
• onDetachedFromWindow()
  當把該組件從某個窗口上分離時觸發該方法
• onWindowVisiblityChanged(int)
  當包含該組件的窗口的可見性發生改變時觸發該方法
• invalidate()
  通知界面重繪(自動調用onDraw()方法)

示例程序:簡單的塗鴉小程序

MainActivity.java

package com.kong.customview;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Adapter;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Spinner;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    CustomView customView;
    LinearLayout layout;
    Button buttonClearScreen;
    Spinner spinnerPaintSize,spinnerPaintColor;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.linearlayout_layout);
        layout = findViewById(R.id.mainLayout);
        customView = new CustomView(MainActivity.this);
        layout.addView(customView);
        buttonClearScreen=findViewById(R.id.buttonClearScreen);
        //當點擊清空屏幕時，將屏幕上的內容清空
        buttonClearScreen.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                customView.clearScreen();
            }
        });
        //尋找下拉框的按鈕
        spinnerPaintSize=findViewById(R.id.spinnerPaintSize);
        spinnerPaintColor=findViewById(R.id.spinnerPaintColor);
        spinnerPaintColor.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                if(position==1)
                {
                    customView.selectPaintColor(Color.rgb(255,0,0));
                }
                else if(position==2)
                {
                    customView.selectPaintColor(Color.rgb(0,255,0));
                }
                else
                {
                    customView.selectPaintColor(Color.rgb(0,0,255));
                }
                if(position!=0)
                {
                    String text=parent.getItemAtPosition(position).toString();
                    Toast.makeText(MainActivity.this,"當前畫筆顏色:"+text,Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
        spinnerPaintSize.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                if(position==1)
                {
                    customView.selectPaintSize(10);
                }
                else if(position==2)
                {
                    customView.selectPaintSize(20);
                }
                else
                {
                    customView.selectPaintSize(30);
                }
                if(position!=0)
                {
                    String text=parent.getItemAtPosition(position).toString();
                    Toast.makeText(MainActivity.this,"當前畫筆尺寸:"+text,Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
    }

}

CustonView.java

package com.kong.customview;

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

import androidx.annotation.ColorInt;

import java.util.ArrayList;
import java.util.Vector;

public class CustomView extends View {
    ArrayList<Float> cirCleVectorX=new ArrayList<Float>();
    ArrayList<Float> cirCleVectorY=new ArrayList<Float>();
    //創建一個畫筆
    Paint paint=new Paint();
    //定義圓的半徑
    int radius=15;
    public CustomView(Context context) {
        super(context);
        //給數組設置初值
        cirCleVectorX.add(new Float(radius));
        cirCleVectorY.add(new Float(radius));
    }

    //當界面被重新繪製時調用該方法
    public void onDraw(Canvas canvas)
    {
        //設置圓心位置、半徑和畫筆
        for(int i=0;i<cirCleVectorX.size();++i)
        {
            //將圓圈初始化在左上角
            canvas.drawCircle(cirCleVectorX.get(i),cirCleVectorY.get(i),radius,paint);
        }
    }
    public boolean onTouchEvent(MotionEvent motionEvent)
    {
        //獲取當前點擊事件的座標
        cirCleVectorX.add(motionEvent.getX());
        cirCleVectorY.add(motionEvent.getY());
        //重繪界面
        invalidate();
        return true;
    }
    //選擇畫筆的粗細
    public void selectPaintSize(int paintSize)
    {
        radius=paintSize;
    }
    //選擇畫筆的顏色
    public void selectPaintColor(int color)
    {
        paint.setColor(color);
    }
    //清空屏幕
    public void clearScreen()
    {
        cirCleVectorX.clear();
        cirCleVectorY.clear();
        invalidate();
    }
}

linearlayout_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mainLayout"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <Button
            android:id="@+id/buttonClearScreen"
            android:text="清空屏幕"
            android:layout_width="0dp"
            android:layout_weight="1"
            android:layout_height="wrap_content">
        </Button>
        <Spinner
            android:id="@+id/spinnerPaintSize"
            android:entries="@array/paintSize"
            android:layout_width="0dp"
            android:layout_weight="1"
            android:layout_height="wrap_content">
        </Spinner>
        <Spinner
            android:id="@+id/spinnerPaintColor"
            android:entries="@array/paintColor"
            android:layout_width="0dp"
            android:layout_weight="1"
            android:layout_height="wrap_content">
        </Spinner>
    </LinearLayout>
</LinearLayout>

arrays.xml

在res/values下創建arrays.xml
屬性名必須： string-array

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="paintSize">
        <item>全部</item>
        <item>10</item>
        <item>20</item>
        <item>30</item>
    </string-array>
    <string-array name="paintColor">
        <item>全部</item>
        <item>紅色</item>
        <item>綠色</item>
        <item>藍色</item>
    </string-array>
</resources>