android - 如何使用 onDraw/drawRect 根据 mainActivity 中的 editText 制作一个矩形
问题描述
基本上我试图从用户那里收集房间的大小..(例如 20x20 大小的房间)。使用在 mainActivity 上收集的这些维度,将该数据发送到 Result Activity 并使用 onDraw/onMeasure 创建一个简单的框。
简而言之,我想从用户那里收集 mainActivity 中框的大小。然后在结果活动中显示盒子的完整图像。
我已经使用从一个活动到另一个活动的数据完成了传递意图。它使用收集到的数据来绘制我遇到问题的形状。
public class MainActivity extends AppCompatActivity {
//variables
Button btnCalculate, btnReset;
Spinner spinSpeaker;
EditText editLength, editWidth, editHeight;
String t1,t2,t3;
int numLength, numWidth, numHeight, numResult=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//connecting variables to GUI elements
btnCalculate= findViewById(R.id.btnCalculate);
btnReset = findViewById(R.id.btnReset2);
spinSpeaker = findViewById(R.id.spinSpeaker);
editLength= findViewById(R.id.editLength);
editWidth = findViewById(R.id.editWidth);
editHeight = findViewById(R.id.editHeight);
//adding function to the calculate button
btnCalculate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//parsing text to integers
t1=editLength.getText().toString();
t2=editWidth.getText().toString();
t3=editHeight.getText().toString();
if (t3.equals("")) {
editHeight.setText("11");
}else if (t2.equals("")) {
editWidth.setText("11");
}else if (t1.equals("")) {
editLength.setText("11");
}else{
numLength = Integer.parseInt(t1);
numWidth = Integer.parseInt(t2);
numHeight = Integer.parseInt(t3);
}
//alert to contact Pro design
if ((numLength>=999)||(numWidth>=999)||(numHeight>=20)) {
Toast.makeText(MainActivity.this, R.string.contactPro,
Toast.LENGTH_LONG).show();
}else {
//calculating volume
numResult = numHeight * numWidth * numLength;
//sending data to other activities
Intent intent = new Intent(MainActivity.this, Result.class);
intent.putExtra("varHeight", numHeight);
intent.putExtra("varWidth", numWidth);
intent.putExtra("varLength", numLength);
intent.putExtra("varResult", numResult);
startActivity(intent);
}
}
});
}
//Result activity
public class Result extends AppCompatActivity {
TextView tim;
MyCanvas mycanvas;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mycanvas = new MyCanvas(this);
setContentView(R.layout.activity_result);
setContentView(Jim);
//Pulling variables from main activity
Intent variables = getIntent();
//int length = variables.getIntExtra("varLength",0);
//int width =variables.getIntExtra("varWidth",0);
int totalResult = variables.getIntExtra("varResult",0);
//showing total
String result = String.valueOf(totalResult);
tim = findViewById(R.id.txtResult);
tim.setText(result);
//Calling the reset button method
configureResetBtn();
}
public void configureResetBtn(){
Button btnReset=findViewById(R.id.btnReset2);
btnReset.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//startActivity(new Intent(Result.this, MainActivity.class));
finish();
}
});
}
}
//MyCanvas activity
public class MyCanvas extends AppCompatActivity {
public MyCanvas(Result result) {
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent variables = getIntent();
final int length = variables.getIntExtra("varLength", 0);
final int width = variables.getIntExtra("varWidth", 0);
class Jim extends View {
Paint paint = new Paint();
Rect rect = new Rect();
public Jim(Context context) {
super(context);
}
@Override
protected void onDraw(android.graphics.Canvas canvas) {
super.onDraw(canvas);
paint.setStrokeWidth(3);
canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), paint);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
setMeasuredDimension(length,width);
}
}
}
}
预期结果是显示一个基于用户的尺寸框(例如 20x20)。但是我收到此错误:
java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)”
但是当我删除试图绘制框的代码时,我的按钮会起作用。
解决方案
而不是设置内容视图两次在ResultActivity
使用SurfaceView
中R.layout.activity_result
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<SurfaceView
android:id="@+id/surface_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />
//....
</FrameLayout>
在结果活动中
SurfaceView surfaceView = findViewById(R.id.surface_view);
surfaceView.getHolder().addCallback(new Callback() {
@Override
public void surfaceCreated(SurfaceHolder holder) {
Canvas canvas = holder.lockCanvas();
// draw
Paint paint = new Paint();
paint.setStrokeWidth(3);
canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), paint);
holder.unlockCanvasAndPost(canvas);
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
});
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